Big Ideas Simply Explained - The Astronomy Book

300 DARK ENERGY T he Big Bang theory has It’s everywhere, really. It’s at its heart a simple idea— between the galaxies. It is in IN CONTEXT the universe started out very small and then expanded. this room. We believe that KEY ASTRONOMERS In 1998, two teams of scientists everywhere that you have Saul Perlmutter (1959–) discovered that the expansion of space, empty space, you Brian Schmidt (1967–) the universe is itself speeding up. cannot avoid having some Adam Riess (1969–) This discovery revealed that what astronomers can directly detect of this dark energy. BEFORE makes up just 5 percent of the total Adam Riess 1917 Albert Einstein adds a mass and energy in the universe. cosmological constant to his Invisible dark matter makes up galaxies are not only moving away field calculations to keep the another 24 percent, while the from Earth; they are expanding universe static. rest is a mysterious phenomenon, away from everywhere all at once. known simply as dark energy. 1927 Georges Lemaître In 2011, three Americans, Saul Better picture suggests that the universe Perlmutter, Brian Schmidt, and Subsequent observations helped could be dynamic, not static. Adam Riess, won the Nobel Prize to tell the history of the expanding for Physics for this discovery. universe. The 1964 discovery of 1928 Edwin Hubble finds the cosmic microwave background evidence of cosmic expansion. Expanding space (CMB), a cold glow left over The year after Georges Lemaître’s from the Big Bang, showed 1948 Fred Hoyle, Hermann paper hypothesized the Big Bang, that the universe has been Bondi, and Thomas Gold Edwin Hubble found proof of the expanding for approximately propose the steady-state theory expanding universe when he 13.8 billion years. Surveys of of the expanding universe. showed that galaxies were moving away from Earth—and the ones AFTER that were farther away were 2013 The Dark Energy Survey moving faster. These were not begins to map the universe. simply objects blasting away from each other through space; this was 2016 The Hubble Space space itself growing in size and Telescope shows that cosmic moving the matter with it. The acceleration is 9 percent faster than originally measured. The expansion of the universe is Measuring this deceleration should reveal assumed to be slowing down due the ultimate fate of the universe. to the force of gravity. However, when measured, cosmic expansion is found to be accelerating. This acceleration must be due to a previously unknown force that works against gravity, called dark energy.

THE TRIUMPH OF TECHNOLOGY 301 See also: The theory of relativity 146–53 ■ Spiral galaxies 156–61 ■ The birth of the universe 168–71 ■ Beyond the Milky Way 172–77 ■ Searching for the Big Bang 222–27 ■ Dark matter 268–71 ■ Redshift surveys 274–75 the large-scale structure of the By the mid 1990s, two programs If you’re puzzled by what universe have since revealed that were under way to measure the dark energy is, you’re billions of galaxies are clustered rate of expansion of the universe. in good company. together around vast empty voids The Supernova Cosmology Project Saul Perlmutter (p.296). This structure corresponds was headed by Saul Perlmutter to minute ripples in the CMB that at Lawrence Berkeley National 1995. The survey found that type show how observable matter—the Laboratory, while Brian Schmidt, 1a supernovae could be used as stars and galaxies—emerged in based at the Australian National standard candles, or objects that anomalous regions in otherwise University, led the High-Z Supernova can be used to measure distances empty space. However, the future Search Team. Adam Riess, of across space. A standard candle of the universe was uncertain. It the Space Telescope Science is an object of known brightness, ❯❯ was unknown whether it would Institute, was the lead author expand forever or one day collapse for the latter project. The project under its own gravity. leaders considered merging, but had different ideas about how Decelerating universe to proceed, and so opted instead Throughout the 20th century, for a healthy rivalry. cosmologists assumed that the rate of expansion was slowing down. Both projects were using a Following a rapid initial expansion, discovery made by the Calán/ gravity would start decelerating. Solodo Supernova Survey, carried It seemed there were two main out in Chile between 1989 and possibilities. If the universe was heavy enough, its gravity would eventually slow the expansion to a stop and begin to pull matter back together in a cataclysmic Big Crunch, a kind of Big Bang in reverse. The second possibility was that the universe was too light to stop the expansion, which would therefore continue forever, gradually slowing down. This process would result in heat death, where the material of the universe had broken up, become infinitely dispersed, and ceased to interact in any way at all. A measurement of the deceleration of the universe’s expansion would tell cosmologists which possible future the universe was heading for. The Chandra X-ray Observatory took this image of the remnant of type 1a supernova SN 1572 in Cassiopeia. It is also known as Tycho’s nova, as it was observed by Tycho Brahe.

302 DARK ENERGY and so its apparent magnitude the temperature and pressure are A computer simulation shows a (brightness as seen from Earth) such that a runaway nuclear fusion white dwarf star exploding in a type 1a shows how far away it is. explosion ignites the star, creating supernova. A flame bubble forms inside an object billions of times brighter the star (left), rises above the surface A type 1a supernova is a little than the sun. (center), and envelops the star (right). different from a standard supernova, which forms when large stars run Distance and motion The brightness, or magnitude, of out of fuel and explode. A type 1a Both surveys used the Cerro Tololo each star gave the distance—often forms in a binary star system, in Inter-American Observatory in billions of light-years—while its which a pair of stars orbit each Chile to find type 1a supernovae. redshift indicated its speed relative other. One is a giant star, the other The plan was not simply to plot the to Earth, caused by the expansion is a white dwarf. The white dwarf’s positions of the supernovae. They of the universe. The teams were gravitational pull hauls stellar used the Keck Telescope in Hawaii aiming to measure the rate at material over from the giant. The to take spectra of each explosion, which the expansion was changing. material accretes on the surface of giving its redshift (the lengthening The rate of expansion, as indicated the white dwarf until it has grown the spectra have undergone). by more distant objects, was to 1.38 solar masses. At this point, expected to be tailing off. Exactly In 2013, the Dark Energy Survey how fast it was doing this would Dark Energy Survey began a five-year project to map show if the universe was “heavy” the expansion of the universe or “light.” However, when the teams in detail. The project uses the looked beyond about 5 billion light- Dark Energy Camera (left) at years (meaning that they were Cerro Tololo Inter-American looking 5 billion years into the Observatory, Chile. The camera past), they found that the opposite has one of the widest fields of was happening—the expansion view in the world. In addition to of the universe was not slowing searching for type 1a supernovae, down but speeding up. the project is looking for baryon acoustic oscillations. These are Dark energy regular ripples in the distribution This result was first thought to of normal matter about 490 million be an error, but successive checks light-years apart, which can be showed it was not—and both used as a “standard ruler” to teams found the same thing. In show up cosmic expansion. 1998, Perlmutter and Schmidt went

THE TRIUMPH OF TECHNOLOGY 303 public with their findings. The This discovery has led us particles, which exist for a Planck results shook the scientific world. to believe that there is some time (10-43 seconds, the smallest Using Einstein’s field equations for unknown form of energy that possible amount of time) and then general relativity, Adam Riess had is ripping the universe apart. disappear again. Dark energy may found that the results appeared to match this idea—a form of energy give the universe a negative mass. Brian Schmidt arising from these virtual particles, In other words, it appeared that which creates a negative pressure a kind of antigravity force was expanding or contracting— that pulls space apart, and pushing matter apart. This source Einstein dropped the constant from represents a nonzero value for of energy was named dark energy, his theories, calling it a mistake. the cosmological constant. because it was a complete mystery. The value of Einstein’s The expansion was not always In 2016, new observations were cosmological constant is set to accelerating. There was a time used to calculate a more accurate, match the energy contained in when gravity and other forces and slightly faster, figure for the a vacuum—in empty space. This pulled matter together and was acceleration of the universe’s was assumed to be zero. However, more powerful than dark energy. expansion. If dark energy continues according to quantum theory, However, once the universe to push the universe apart (it may even a vacuum contains “virtual” became big and empty enough, not, no one really knows), it will the effects of dark energy appear disperse the galaxies so that to have become dominant. It may eventually they would all be too far be that a different force takes over away to be seen from Earth (which in the future, or dark energy’s itself will no longer exist). Eventually, effects may continue to grow. One it may scatter the stars within the suggestion is that a Big Rip would Milky Way until the sky goes dark. be so powerful that dark energy will The sun and the planets in the solar tear apart spacetime itself, creating system would be pulled apart, and a singularity—the next Big Bang. ■ finally the particles in atoms will also be scattered, resulting in a form Four possible futures of heat death dubbed the Big Rip. Reviving Einstein’s mistake If the average If the density If the density Observations Dark energy may indicate that the density of the is equal to the is below the suggest that universe is not as homogenous as universe is above critical density, critical value, the the universe’s cosmologists think it is, and that a certain critical the universe’s universe should expansion is the apparent acceleration seen is value, it should geometry will be open and accelerating due due to the fact that it is inside a be closed, and be flat, and the expand forever, to mysterious region with less matter in it than end with a Big universe ought to to end eventually “dark energy.” elsewhere. It may also be showing Crunch. The continue into the in a heat death. The measured that Einstein’s theory of gravity critical value is future, neither density is very is incorrect on the largest scales. On estimated to be expanding nor close to the the other hand, dark energy might the equivalent of contracting. critical density, also be explained by a mathematical five protons per but dark energy device Einstein created in 1917 cubic meter. is accelerating called the cosmological constant. expansion. Einstein used this as a value that would counteract the pull of gravity and make the universe a static, unchanging place. However, when Lemaître used Einstein’s own equations to show that the universe could only be dynamic—

304 BPOEIVLEELRRIION1N3G.Y5BEAACRKS STUDYING DISTANT STARS IN CONTEXT T he James Webb Space An artist’s impression of the JWST Telescope (JWST) is in space shows the layered stack of KEY DEVELOPMENT designed to be the most the sunshield unfolded beneath the James Webb Space powerful astronomical tool in space, telescope. The beryllium mirror is Telescope (2002–) able to see farther than even the coated in gold for optimal reflection. Hubble Space Telescope. Named BEFORE in 2002 after the NASA director Conceived in 1995 as the successor 1935 Karl Jansky shows that who oversaw the Apollo program, to Hubble, the JWST has had a long radiation other than light can the JWST is an infrared telescope road to completion, encountering be used to view the universe. equipped with a 21-ft (6.5-m)-wide multiple technical hurdles. When gold-plated mirror. This will allow launched in 2018, it will take up 1946 Lyman Spitzer Jr suggests it to see more than 13.5 billion a tight orbit around L2 (Lagrange placing telescopes in space to light-years into the distance—to point 2), a location 1 million miles avoid atmospheric interference. the time when the universe’s first (1.5 million kilometers) beyond stars were forming. Earth’s orbit, away from the sun. 1998 The Sloan Digital Sky Survey begins to make a 3D map of the galaxies. AFTER 2003 The Spitzer Space Telescope, an infrared observatory, is launched. 2014 The European Extremely Large Telescope project is approved, with a primary mirror 39 m (128 ft) in diameter. 2016 LIGO announces the discovery of gravitational waves, suggesting a possible means for looking even farther than the JWST.

THE TRIUMPH OF TECHNOLOGY 305 See also: Radio astronomy 179 ■ Space telescopes 188–95 ■ A digital view of the skies 296 ■ Gravitational waves 328–31 ■ Lagrange (Directory) 336 The light from the first stars has been shining through expanding space. The expansion has Infrared is mostly To see the first stars, stretched the light into invisible from a giant infrared infrared wavelengths. Earth’s surface. telescope must be sent into space. L2 is a place in space where the that penetrates the top layer is then are a prime target of observation gravity of the sun and Earth work radiated sideways by successive for the JWST. At the same time, together to pull an orbiting object inner layers so that almost nothing this ultra-sensitive eye on the around the sun at the same rate as reaches the telescope itself. infrared sky has three other main Earth, making one orbit every year. goals. It will investigate how This means the JWST will be largely First light galaxies have been built over in the shadow of Earth, blocking The light waves from the first stars billions of years, study the birth of out any heat pollution from the to form have been stretched as stars and planets, and provide data sun and allowing the telescope they shine through the expanding about extrasolar planets. NASA to detect very faint infrared sources universe, changing them from hopes that the telescope will be in deep space. NASA claims that visible light to infrared, so they in operation for at least 10 years. ■ the telescope could detect the heat of a bumblebee on the moon. L4 Heat seeker Earth’s orbit The JWST’s vast primary mirror is seven times the area of Hubble’s JWST’s orbit and, instead of polished glass, the mirror contains 18 hexagonal units L3 L2 made from beryllium for maximum L1 reflection. The 270-sq-ft (25-m2) mirror is too large to be launched Moon’s orbit flat, so it is designed to unfold once in orbit. L5 To pick up the faint heat JSWT will not be exactly at the L2 point, but will circle around it in signatures of the most distant stars, a halo orbit. Lagrange points are positions in the orbit of two large bodies the telescope’s detectors must where a smaller object can keep a stable position relative to those two large always be extremely cold—never bodies. There are five L points in the orbital plane of Earth and the sun. more than –370°F (–223°C). To accomplish this, the JWST has a heat shield the size of a tennis court. Again, this is folded away for launch. The shield is made from five layers of shiny plastic that reflect most of the light and heat. Any heat

OUR MISSION COMETIS TO LAND ON A UNDERSTANDING COMETS



308 UNDERSTANDING COMETS IN CONTEXT B y studying comets, Giotto ignited the planetary astronomers hope to science community in Europe. KEY DEVELOPMENT shed new light on ESA—Rosetta (2004) various questions about the early Gerhard Schwehm solar system, the formation of BEFORE Earth, and even the origins of life. Giotto Project scientist 1986 The Halley Armada of eight spacecraft, led by ESA’s Earth is the only planet known rock. This revived the theory that Giotto, make observations to have a surface ocean of liquid this is where Earth’s oceans came of Halley’s comet. water. The origin of this water is from. One theory concerning the one of the enduring mysteries of origin of life was that the complex 2005 The Deep Impact Earth science. A leading theory is chemical building blocks necessary mission fires a probe at comet that the hot, young planet sweated for life, such as amino acids and Tempel 1 to create a crater out the water from its rocks, nucleic acids, arrived on Earth in the surface, and analyzes releasing water vapor into the from space. Perhaps these organic what is underneath. atmosphere. Once the planet compounds were also delivered to had cooled sufficiently, this vapor Earth by comets. The only way to 2006 The Stardust mission condensed and fell as a deluge of find out was to send a spacecraft collects a capsule of cometary rain that filled the oceans. Another to meet up with a comet and land dust from the tail of comet theory argues that at least some on its surface. In 2004, the ESA-led Wild 2 and returns to Earth. of the water arrived from space, Rosetta mission blasted off on a specifically in the hundreds of 10-year journey to do just that. AFTER thousands of icy comets that rained 2015 New Horizons flies down on Earth during the first half Fresh target by Pluto and begins an billion years of its existence and Rosetta’s intended target exploration of the Kuiper belt. vaporized on impact. was Comet 67P/Churyumov– Gerasimenko, or 67P for short. In 2016 NASA’s OSIRIS-REx A flyby of Halley’s comet in 1959, this comet had been captured spacecraft is launched with a 1986 by a flotilla of spacecraft led by by the gravity of Jupiter, which had mission to collect and return ESA’s Giotto got the first close-up pulled it into a shorter six-year orbit a sample from the asteroid look at a comet’s core, or nucleus. of the sun. Before that, 67P had 101955 Bennu. The Halley encounter provided been circling the sun much farther conclusive proof that comets are away. This excited the Rosetta largely made from water ice mixed scientists because the tail of a with organic dust and chunks of comet—its most familiar feature— is caused by solar radiation heating the surface of the nucleus, which In 2005, the Deep Impact impactor collided with comet Tempel 1, releasing debris from the comet’s interior. Analysis showed the comet to be less icy than expected.

THE TRIUMPH OF TECHNOLOGY 309 See also: The Oort cloud 206 ■ The composition of comets 207 ■ Investigating craters 212 ■ Exploring beyond Neptune 286–87 ■ Studying Pluto 314–17 Comets are the leftovers from the formation of the planets. Earth’s water and the chemicals needed for life may have come from comets. creates streams of dust, gas, and An artist’s impression shows To find out, plasma hundreds of millions of Rosetta releasing the Philae lander we need to land miles long. The material in the tail above comet 67P. The lander bounced is lost from the comet forever. 67P on landing, flying up from one lobe of on a comet. had only been close to the sun a the comet to land again on the other. handful of times in its existence. First indications That meant it was still “fresh” with a central body about as large are that Earth’s water and its primordial composition intact. as a small van. A folded solar organic chemicals did not array unfurled to provide 690 sq ft All aboard (64 m2) of photovoltaic cells, which come from comets. Rosetta was launched by an Ariane would power the craft throughout 5 rocket from ESA’s space center the mission. the surface, Philae would pick up in French Guiana. The spacecraft signals from CONSERT, sent out weighed just under 3 tons, with Most of Rosetta’s instruments while Rosetta was orbiting on were designed to study the comet the far side. Philae was equipped We didn’t just land once— while in orbit. They included various with solar panels and rechargeable maybe we landed twice! spectroscopes and microwave batteries and was designed to radars for studying the composition work on the comet’s surface in Stephan Ulamec of the comet surface and the dust order to analyze its chemistry. and gases that would be released Philae landing manager when 67P neared the sun and Both the names Rosetta and began to heat up. One of the most Philae referred to ancient Egyptian important instruments on board artifacts. The Rosetta Stone was CONSERT (Comet Nucleus has a carved inscription in three Sounding Experiment by Radiowave languages: Hieroglyphs, Demotic Transmission), which would blast Egyptian, and ancient Greek. ❯❯ a beam of radio waves through the comet to find out what lay inside. CONSERT would operate with the help of the lander Philae. Once on

310 UNDERSTANDING COMETS and was soon bearing down on We are on the surface of the 67P at great speed. For the journey comet! Whatever we do has to deep space, Rosetta had been never been done before. The powered down to save energy, data we get there is unique. but it powered back up and contacted Earth on schedule as it Matt Taylor neared the comet in August 2014. Rosetta’s controllers then began Rosetta Project scientist a series of thruster burns to make Rosetta zigzag through space and slow from 2,540 ft/s (775 m/s) to 26 ft/s (7.9 m/s). On September 10, the spacecraft went into orbit around 67P, offering the first look at the target world. Rosetta captured this image of Bumpy landing A landing zone on the “head” of comet 67P/Churyumov−Gerasimenko Comet 67P is about 2.5 miles (4 km) the comet was selected, and at 8:35 on July 14, 2015, from a distance of long and turned out to be more GMT on November 12, 2014, Philae 96 miles (154 km), as the comet irregular in shape than expected. was released from Rosetta. It took neared its closest point to the sun. From some viewpoints, the comet almost eight hours to confirm that looks like a vast rubber duck, with its Philae was on the surface, much In the early 19th century, it two lobes, one larger than the other, longer than expected. The lander allowed scholars to decipher the connected by a narrow neck. (It is was designed to touch down at a hieroglyphic writing system, thus assumed the comet was formed slow speed—slower than an object unlocking the meaning of many from two smaller objects making dropped from shoulder height ancient Egyptian writings. Philae a low-speed impact.) The surface on Earth—and attach itself to refers to an obelisk with multiple was riddled with boulder fields the ground using harpoons fired inscriptions that was used in a and ridges, and the Rosetta team from the tips of its legs. However, similar way. Comets are remnants struggled to find a clear location something had gone wrong. It is left over from the formation of the to set down the Philae lander. solar system, so these names were chosen because the Rosetta and Rosetta received gravity assists from both Earth and Mars en Philae missions at comet 67P route to Comet 67P. As it swung around the planets, their gravitational were intended as a way to unlock fields threw the spacecraft forward at greatly increased speed. new knowledge of the primordial material that formed the planets. Launch November 13, 2007 March 2, 2004 2nd Earth gravity assist Comet cruise 4 Rosetta took a circuitous route to the comet, using three flybys 21 February 25, 2007 of Earth and one of Mars (a 1st Earth Mars gravity assist risky maneuver, skimming its gravity assist atmosphere only 150 miles [250 km] 3 up) to boost speed through gravity assists. This process took five June 8, 2012 years, after which Rosetta had Enters deep space hibernation enough speed to fly through the 5 asteroid belt (getting a very close look at some asteroids), and out beyond the orbit of Jupiter. There, it began to swing back around,

THE TRIUMPH OF TECHNOLOGY 311 On July 16, 2016, Rosetta was just 8 miles (12.8 km) from the center of comet 67P. This image covers an area about 1,500 ft (450 m) across. It shows a dust-covered rocky surface. thought that the lander landed of the ways in which the comet September 30 by making a controlled awkwardly and hit a boulder, and was changing as it entered the crash-landing, returning data right the very low gravity of the comet warmer part of the solar system. up to the moment of impact. meant Philae bounced right off again. It was later calculated that In mid-June 2015, Philae received Alien water Philae bounced up about 3,000 ft enough sunlight to wake up, and The amount of deuterium (“heavy (1 km) from the surface before falling began intermittent communication hydrogen”) found in 67P’s water back again, tumbling to a resting with Rosetta, allowing further is much greater than in the water place on the edge of the target CONSERT scans. In early July, found on Earth, evidence against landing zone. Unfortunately, the however, it fell silent again. the idea that Earth’s water is of lander ended up in the shadow of a Fortunately, it was spotted by the extraterrestrial origin. The mission cliff and appeared to be at an angle. OSIRIS camera on September 2, has found many carbon-based Without sunlight to recharge its 2016, as it approached within compounds, but only one amino acid batteries, Philae had only about 1.7 miles (2.7 km) of the comet. (the building block of proteins) and 48 hours of power to perform its Knowing Philae’s precise landing no nucleic acids (the ingredient of primary science missions, returning spot allows scientists to place the DNA) have been detected in the data. data on the chemical composition information it sent back a year of the dust and ice, and performing earlier into context. Rosetta’s results will allow scans with the CONSERT astronomers to better understand instrument on Rosetta. A last-ditch After comet 67P passed comets and whether 67P is a typical plan to push the lander out into the perihelion in August 2015, the body. Combined with discoveries sunlight using the harpoons (which solar power available to Rosetta fell from the Kuiper belt, this is hoped had not fired on landing) failed, and rapidly. In September 2016, Rosetta to reveal what the solar system was Philae shut down into safe mode. was instructed to get slowly nearer made of as the sun formed. ■ to the comet. It ended its mission on Approaching the sun Despite this setback, the perilous Philae landing was deemed a success. The hope was that Philae’s shaded location would become sunnier as the comet approached the sun. The comet would reach its perihelion, or closest point, in August 2015. On the approach, comet 67P began to heat up and its surface erupted with jets of dust and plasma. Rosetta was sent on a complex orbital path so that it could fly low over the comet and pass through the denser regions of the coma, or cloud of material, that was forming around 67P. Its path also took it farther out, providing a more complete picture

312   STB  HOIRELTAVHRIOOSLFYESTNHTTEEM THE NICE MODEL IN CONTEXT B y the start of the 21st Surrounding all these bodies was century, the solar system a distant sphere of comet material, KEY ASTRONOMERS was known to contain many called the Oort cloud. Rodney Gomes (1954–) kinds of object. In addition to the Hal Levison (1959–) planets and the asteroid belt, there It was difficult to explain how Alessandro Morbidelli (1966–) were cometlike bodies called a system like this had evolved Kleomenis Tsiganis (1974–) centaurs located in between the from a proto-solar cloud of dust giant planets, trojan asteroids and gas. Evidence from extra-solar BEFORE sharing the orbits of many planets, systems showed that giant planets 1943 Kenneth Edgeworth and the outer Kuiper belt had were often much closer to their suggests that Pluto is just also just been discovered. star than was previously thought one of many objects in the possible. It was at least feasible, outer solar system. The solar system is filled therefore, that the giant planets of with many kinds of object, Earth’s solar system had formed 1950 Jan Oort suggests that closer to the sun. long-period comets come from all orbiting the sun. a distant cloud surrounding Planetary migration the solar system. The arrangement of these In 2005, four astronomers in Nice, objects formed as the France, used computer simulations 1951 Gerard Kuiper proposes to develop a theory to explain the that a comet belt existed outermost planets Saturn, evolution of the solar system. beyond Pluto in the early Uranus, and Neptune This is now known as the Nice stages of the solar system. model. They suggested that migrated out from the sun. the solar system’s three outer 1993 American planetary planets, Saturn, Uranus, and scientist Renu Malhotra The outermost planets Neptune, were once much closer suggests that planet migration swept away a vast disk to the sun than they are now. took place in the solar system. of material, leaving the Jupiter was slightly farther away than it is now at 5.5 astronomical 1998 The Kuiper belt is system seen today. units (AU), but Neptune was much confirmed to exist. closer, at 17 AU (it now orbits at 30 AU). From Neptune’s orbit, a AFTER vast disk of smaller objects called 2015 Spacecraft New Horizons planetesimals spread to 35 AU. reaches the Kuiper belt. The giant planets pulled these

THE TRIUMPH OF TECHNOLOGY 313 See also: The discovery of Ceres 94–99 ■ The Kuiper belt 184 ■ The Oort cloud 206 ■ Investigating craters 212 ■ Exploring beyond Neptune 286–87 Rodney Gomes similar to those used in building The Nice model changed the Nice model to understand the whole community’s Brazilian scientist Rodney the motion of several Kuiper belt perspective on how the planets Gomes is a member of the Nice objects (KBOs) that appear to formed and how they moved model quartet of scientists that be following unusual orbits. In in these violent events. came to prominence in 2005. 2012, he shook up the accepted It also includes American Hal view of the solar system yet Hal Levison Levison, Italian Alessandro again. Gomes proposes that a Morbidelli, and Greek Kleomenis Neptune-sized planet (four times Tsiganis. Gomes, who has as heavy as Earth) is orbiting worked at Brazil’s national 140 billion miles (225 billion km) observatory in Rio de Janeiro from Earth (at 1,500 AU) and since the 1980s, is a leading that this mysterious planet expert in the gravitational is distorting the orbits of the modeling of the solar system, KBOs. The search is now on and has applied techniques to locate this “Planet X.” planetesmials inward and, in of thousands of meteorites were asteroid belt. Planetesimals were return, Saturn, Uranus, and Neptune punched from the outer disk and also scattered farther out, including started slowly edging farther away rained down on the inner planets. the dwarf planets Sedna and Eris, from the sun. Planetesimals discovered in 2003 and 2005. encountering Jupiter’s powerful Much of the planetesimal disk gravity were fired out to the edge became the Kuiper belt, tied to The Nice model works well for of the solar system to form the Neptune’s orbit at 40 AU. Some many starting scenarios for the Oort cloud, and this had the effect planetesimals were captured by solar system. There is even one of shifting Jupiter inward (its the planets to become moons, in which Uranus is the outermost current orbital distance is 5.2 AU). others filled stable orbits as trojans, planet, only to swap places with and some may have entered the Neptune 3.5 billion years ago. ■ Resonant orbit Eventually, Saturn shifted to a resonant 1:2 orbit with Jupiter, which meant that Saturn orbited once for every two orbits of Jupiter. The gravitational effects of this resonant orbit swung Saturn, then Uranus and Neptune into more eccentric orbits (on more stretched ellipses). The ice giants swept through the remaining planetesimal disk, scattering most of it, to create what is known as the Late Heavy Bombardment, which occurred about 4 billion years ago. Tens During the Late Heavy Bombardment, the moon would have glowed as it was struck by meteorites. Most of the early Earth’s surface was volcanic.

314 IN CONTEXT SOVAIODCEDLWLABORAOSLEFSL-YAUOSNPFTETMHE KEY ASTRONOMER Alan Stern (1957–)  STUDYING PLUTO BEFORE 1930 Clyde Tombaugh discovers Pluto, which is named as the ninth planet. 1992 Pluto is found to be one of many Kuiper Belt Objects orbiting the sun beyond Neptune. 2005 Another Pluto-sized object is found beyond the orbit of Neptune. It is called Eris. AFTER 2006 Pluto, Eris, and several other objects are reclassified as dwarf planets. 2016 A skewing of the orbits of Kuiper Belt Objects suggests that there is a Neptune-sized planet much farther out in space, orbiting the sun every 15,000 years. The search is now on for this object. I n January 2006, NASA’s New Horizons spacecraft lifted off from Cape Canaveral on a voyage to the planet Pluto and beyond. The moment was testament to the perseverance of the principal investigator for New Horizons, Alan Stern. Planetary demotion At the time, nobody knew what Pluto actually looked like. It was small and far away on the inner rim of the Kuiper belt, and even the mighty Hubble Space Telescope could only render it as a pixelated ball of light and dark patches. Plans to explore Pluto close-up were thwarted during the 1990s as NASA budgets were

THE TRIUMPH OF TECHNOLOGY 315 See also: The Oort cloud 206 ■ The composition of comets 207 ■ Exploring the solar system 260–67 ■ Exploring beyond Neptune 286–87 Just as a Chihuahua is still was a planet at all. The IAU agreed Alan Stern a dog, these ice dwarfs that the new body, to be named are still planetary bodies. Eris, was not a planet. Its gravity Born Sol Alan Stern in New Alan Stern was too weak to clear other bodies Orleans, Louisiana, in 1957, from its orbit. The planets from Stern’s fascination with squeezed. By 2000, the plans had Mercury to Neptune are big enough Pluto began in 1989 when been shelved, but Stern made the to do this, but the bodies of the he worked with the Voyager case for sending a mission to Pluto, asteroid belt manifestly are not— program. While he was there, the smallest, most distant planet, and nor was Pluto. However, Stern witnessed the final which had been discovered by US Pluto and Eris were not like most encounter of Voyager 2 astronomer Clyde Tombaugh in 1930. asteroids. They were massive as it flew past Neptune and its enough to be spherical rather than moon Triton. Triton appeared In 2003, Stern’s New Horizons irregular chunks of rock and ice. as a ball of ice, and looked proposal was given the green So the IAU created a new class of very much like the Pluto light, and the 2006 launch set the object: that of dwarf planet. Pluto, Stern and other scientists spacecraft on a nine-year flight to Eris, and several large Kuiper Belt had imagined. (Triton is Pluto. It occurred not a moment too Objects (KBOs) were given dwarf thought to be a Kuiper Belt soon. In August 2006, prompted planet status, as was Ceres, the Object that has been captured by the discovery of a possible largest body in the asteroid belt. by Neptune.) tenth planet beyond the orbit of For most of these objects, this was Pluto, the general assembly of the a promotion in the hierarchy of In the 1990s, Stern trained International Astronomical Union the solar system, but not for Pluto. as a Space Shuttle payload (IAU) gathered in Prague to discuss If Pluto had been declassified as specialist (technical expert), issues raised by the new discovery. a planet prior to New Horizons’ but he never got the chance The first question was whether it launch, it is uncertain whether to fly into space. Instead, he the mission would have happened. returned to the study of Pluto, the Kuiper belt, and the Oort Long journey cloud. In addition to leading Although Pluto’s orbit does bring the New Horizons mission it closer to the sun than Neptune as principal investigator, for some of its 248-year revolution Stern is active in developing around the sun, the New Horizons new instruments for space probe had the longest journey to the exploration and more cost- most distant target in the history ❯❯ effective ways of putting astronauts into orbit. Pluto is too far away The only way to to observe details with study Pluto is to send Key work a telescope. a spacecraft. 2005 Pluto and Charon: Ice Worlds on the Ragged Edge The spacecraft has revealed that of the solar system Pluto’s icy structure is a completely new kind of planetary body.

316 STUDYING PLUTO New Horizons’ scientific instruments were Range Reconnaissance Imager), a switched off to conserve power for most of its telescopic camera, would produce 10-year journey, but they were powered up for the highest resolution pictures one month a year so that checks could be made. of the Pluto system; SWAP (Solar Wind Around Pluto) would, as the REX name suggests, observe Pluto’s PEPSSI interaction with the solar wind, while PEPSSI (Pluto Energetic Alice Particle Spectrometer Science Investigation) detected the plasma Ralph given off by Pluto. This would help in understanding the way the SWAP dwarf planet’s atmosphere is formed by sublimation (the change LORRI VBSDC of a solid directly into a gas) from the icy surface during Pluto’s of space exploration—30 AU, or be leaving Pluto behind. It takes “summer” as it nears the sun 2.7 billion miles (4.4 billion km) from radio signals from Pluto 4.5 hours (and then freezes again in winter). Earth. To achieve this, the spacecraft to reach Earth, plus the same again Finally the SDC (Student Dust was given the fastest launch ever, to send a return message. Therefore, Counter) was an instrument blasting off with an escape velocity it would take at least nine hours to operated by university students of 36,373 mph (58,536 km/h). A year make even tiny course corrections, throughout the mission. This after launch, the spacecraft reached by which time the primary mission experiment was renamed VBSDC Jupiter. In addition to making some would be almost over. for Venetia Burney, the British girl observations of the Jovian system, who had proposed the name Pluto. New Horizons used Jupiter’s gravity New Horizons carried seven to gain a 20 percent speed boost. instruments. They included two Destination reached This cut the flight time to Pluto imaging spectrometers, built to New Horizons began its approach in from over 12 years to 9.5 years. work together and named after the January 2015. One of the first things characters in the 1950s US sitcom it did was to make an accurate Instruments on board The Honeymooners. Ralph was the measurement of Pluto’s size. This The precision of the trajectory from visible and infrared spectrometer had always been a tricky problem to Jupiter was crucial to the success of used to make maps of Pluto’s solve. When it was first discovered, New Horizons. If it was just slightly surface, while Alice was sensitive off, the craft would miss Pluto to ultraviolet and was tasked with It used to be that Pluto was a altogether. The main observation studying Pluto’s thin atmosphere. misfit. Now it turns out that window was about 12 hours long, REX (Radio science EXperiment) after which New Horizons would would take the temperature of Earth is the misfit. Most Pluto and its moons; LORRI (Long planets in the solar system look like Pluto, and not like the terrestrial planets. Alan Stern

THE TRIUMPH OF TECHNOLOGY 317 it was estimated that Pluto was (12,472 km) above Pluto, its closest This view from New Horizons zooms seven times the size of Earth. By approach. Its instruments were in on the southeastern portion of 1978, it was clear that Pluto was collecting huge quantities of Pluto’s great ice plains, where the smaller than Earth’s Moon. However, data to be fed back to Earth. plains border rugged, dark highlands. it also had a huge satellite, named The close-up view of Pluto showed Charon (the boatman of the dead in it to be a world of pale ice plains are named after past missions: Greek mythology), which was about and dark highlands. The ice is Voyager, Venera, and Pioneer. Two a third of the size of Pluto, and the largely frozen nitrogen, which main mountain ranges have been two bodies moved around each makes Pluto a very bright object imaged clearly: Norgay Montes and other as a binary system. At launch, for its size. The highlands are also Hillary Montes, named after the first planners also took into account two ice (although mixed with tar-like two climbers to reach the summit of more tiny moons, Nix and Hydra, hydrocarbons). The ice is thrust Mount Everest. However, the central but by 2012, with New Horizons into lumpy peaks that tower 2 miles feature of New Horizons’ partial already well on the way, it was (3 km) above the plains. Quite map of Pluto is Tombaugh Regio, found that there were two more— how such huge features arose a heart-shaped plain. Half of this Kerberos and Styx—which could on such a cold and small body is area is made up of Sputnik Planitia, potentially disrupt the mission. one of the mysteries of the New a vast ice floe riddled with cracks Horizons mission. In addition, and troughs, but with no craters, Measuring Pluto craterlike structures have been which suggests it is a young feature In the end, these worries were identified as possible ice volcanoes. that is carving out new surface misplaced, and LORRI was able features like glaciers on Earth. to obtain a measurement for all Naming the landmarks of these bodies. Pluto is 1,470 miles Pluto’s surface features have been Now past Pluto, the craft is (2,370 kilometers) wide, meaning given unofficial names by NASA on course to meet up with other that it is larger than Eris (although scientists. Cthulhu Regio is a large KBOs. Its nuclear power source Eris is heavier). On July 14, 2015, whale-shaped dark patch in the should last until around 2030, and New Horizons flew 7,750 miles southern hemisphere. Other regions the mission should make many more discoveries. ■

MARSA LABORATORY ON EXPLORING MARS



320 EXPLORING MARS I n August 2012, the Mars Mars has been flown by, Science Laboratory Rover, orbited, smacked into, IN CONTEXT better known as Curiosity, radar-examined, and rocketed landed on Mars. This 2,000-lb onto, as well as bounced KEY ORGANIZATION (900-kg) wheeled vehicle, which upon, rolled over, shoveled, NASA—Mars exploration is still roaming the Martian surface, drilled into, baked, and even is a mobile laboratory equipped to blasted. Still to come: Mars BEFORE conduct geological experiments 1970 The Soviets’ Lunokhod 1 aimed at figuring out the natural being stepped on. becomes the first vehicle to be history of the red planet. It is the Buzz Aldrin used on another body when it latest robot explorer to reach touches down on the moon. Mars, and the largest and most advanced in a long line of rovers 1971 The Lunar Roving sent to explore other worlds. Vehicle is driven on the moon for the first time during Wanderers spent more than 22 hours outside. NASA’s Apollo 15 mission. The potential of rovers in space In their rover, they covered 22 miles was clear as far back as 1971, (36 km) in total, with one drive 1977 NASA’s Sojourner is when Apollo 15 carried a four-wheel taking the pair 4.7 miles (7.6 km) the first rover to reach Mars. Lunar Roving Vehicle to the moon. from their spacecraft. The Lunar This agile two-seater widened the Roving Vehicle, or moon buggy, AFTER scope of lunar exploration for the was used to collect rocks. The six 2014 Opportunity breaks the last three Apollo missions. For Apollo missions returned to Earth distance record for a rover on instance, during the first moon with 840 lb (381 kg) of them. an extraterrestrial body. landing in 1969, Neil Armstrong and Buzz Aldrin spent just two Analysis of these rocks revealed 2020 The NASA Mars 2020 and a half hours moonwalking, and much about the history of the moon. rover is set to be launched as the farthest they moved from their The oldest were about 4.6 billion a replacement for Curiosity. lunar module was 200 ft (60 m). years old, and their chemical By contrast, however, in the final composition clearly showed a 2020/21 The ExoMars rover Apollo moon mission, Apollo 17, common ancestry with rocks on is due to be deployed by the in 1972, the crew of two—Eugene Earth. Tests revealed no evidence European Space Agency in Cernan and Harrison Schmitt— of organic compounds, indicating Oxia Planum, a depression that the moon has always been filled with clay-bearing rocks. a dry and lifeless world. Lunokhod 1 The Soviet lunar program, which began in the early 1960s, relied on unmanned probes to explore the moon. Three of the Soviet Luna Geologist−astronaut Harrison Schmitt collects samples from the lunar surface during the 1972 Apollo 17 mission. He spent many hours exploring the surface on the moon buggy.

THE TRIUMPH OF TECHNOLOGY 321 See also: The Space Race 242–49 ■ Exploring the solar system 260–67 ■ Understanding comets 306–11 ■ Studying Pluto 314–17 The Soviet Lunokhod 1 rover, seen here in tests on Earth, was the first rover ever to land on an alien world—its predecessor, Lunokhod 0, was launched in 1969 but never reached orbit. probes returned with a total of moon. An X-ray spectrometer as a heater to keep the machinery 11.5 oz (326 g) of rock. Then, in was used to analyze the chemical working. The rover received November 1970, the Soviet lander composition of rocks, and a device commands from controllers on Luna 17 arrived at a large lunar called a penetrometer was pushed Earth about where to go and when plain called the Sea of Rains (many into the lunar regolith (soil) to to perform experiments. A human lunar areas are named after the measure its density. might have done a better job, weather conditions they were once but rovers could stay in space for thought to influence on Earth). Lunokhod was powered by months on end, and did not require Luna 17 carried the remote- batteries that were charged by day food and water from Earth. controlled rover Lunokhod 1 using an array of solar panels that (Lunokhod means “moonwalker”). folded out from the top of the rover. Lunokhod 1 was designed This was the first wheeled vehicle At night, a source of radioactive to work for three months, but to traverse an extraterrestrial world, polonium inside the machine acted lasted almost 11. In January 1973, arriving about eight months before Lunokhod 2 landed in the Le the first Apollo buggy. The concept Over time you could terraform Monnier Crater on the edge of the behind it was simple—instead of Mars to look like Earth … Sea of Serenity. By June, Lunokhod sending moon rocks to Earth, the 2 had traveled a total of 24 miles rover would do the analysis there. So it’s a fixer-upper of a planet. (39 km), a record that would stand Elon Musk for more than three decades. Remote-controlled explorer The Lunokhod rover was 7½-ft Canadian space entrepreneur Martian walker (2.3-m) long and resembled a As Lunokhod 1 was exploring the motorized bathtub. The wheels moon, the Soviet space program were independently powered so was eyeing an even greater prize: that they could retain traction on a rover on Mars. In December 1971, the rough lunar terrain. Lunokhod two Soviet spacecraft, code-named was equipped with video cameras Mars 2 and Mars 3, sent modules that sent back TV footage of the to land on the red planet. Mars 2 crashed, but Mars 3 made a successful touchdown—the first- ever landing on Mars. However, it lost all communications just 14.5 seconds later, probably due to damage from an intense dust storm. Scientists never found out what happened to Mars 3’s cargo: a Prop-M rover, a tiny 10-lb (4.5-kg) vehicle designed to walk on two ski-shaped feet. It was powered through a 50-ft (15-m) umbilical cord, and once on the surface was designed to take readings of the Martian soil. It is unlikely that ❯❯

322 EXPLORING MARS the Prop-M ever carried out its We landed in a nice flat spot. traveled just 300 ft (100 m) during mission, but it was programmed Beautiful, really beautiful. its 83-day mission, and never to operate without input from Adam Steltzner ventured farther than 40 ft (12 m) Earth. A radio signal between from the lander. Now named the the moon and Earth travels in less Lead landing engineer, Curiosity Carl Sagan Memorial Station, the than 2 seconds, but a signal to lander was used to relay data from or from Mars takes between 3 huge protective airbags inflated the rover back to Earth. Most of the and 21 minutes to arrive, varying around the lander, and retrorockets rover’s power came from small solar with the planet’s distance from on the spacecraft holding the tether panels on the top. One of the goals Earth. For a Martian rover to be fired to slow the speed of descent. of the mission was to see how a successful explorer, it needed The tether was then cut, and the these panels stood up to extreme to work autonomously. lander bounced across the Martian temperatures and what power surface until it rolled to a stop. could be generated in the faint Bounce down Fortunately, once the airbags had Martian sunlight. In 1976, NASA’s two Viking landers deflated, the lander was the right sent back the first pictures of Mars. side up. The three upper sides or The rover’s activities were Following this success, many more “petals” of the tetrahedral lander run from NASA’s Jet Propulsion rovers were planned, but most of folded outward, revealing the Laboratory (JPL) in California, and these projects never reached their 24-lb (11-kg) rover. JPL has remained the lead agency destination, succumbing to what the in developing Martian rovers. press dubbed the “Martian Curse.” During development, the With the time delays inherent in rover was called MFEX, short communicating with Mars, it is NASA eventually had a success for Microrover Flight Experiment. not possible to drive a rover in real with its 1997 Mars Pathfinder However, it was known to the time, so every leg of a journey must mission. In July of that year, the public as Sojourner, meaning be preprogrammed. To achieve Pathfinder spacecraft entered the “traveler” and chosen for its link this, cameras on the lander were Martian atmosphere. Slowed first to Sojourner Truth, a 19th-century used to create a virtual model by the friction of a heat shield and US abolitionist and rights activist. of the surface around Sojourner. then by a large parachute, the Human controllers could view the spacecraft jettisoned its outer area in 3-D from any angle before shielding, and the lander inside mapping a route for the rover. was lowered on a 65-ft (20-m) tether. As it neared the surface, Spirit and Opportunity Despite its limitations in terms of size and power, Sojourner’s mission was a great success, and NASA Rolling on Mars Whatever the reason you’re on Sojourner was the first rover to Mars is, I’m glad you’re there. take a tour of the Martian surface. And I wish I was with you. However, the Pathfinder mission was really a test for the innovative Carl Sagan landing system and the technology that would power larger rovers in in a message for future explorers the future. The minuscule vehicle During its 83 days of operation, the tiny Sojourner rover explored around 2,691 sq ft (250 sq m) of the planet’s surface and recorded 550 images.

THE TRIUMPH OF TECHNOLOGY 323 An artist’s impression portrays a NASA Mars Exploration Rover. Rovers Opportunity and Spirit were launched a few weeks apart in 2003 and landed in January 2004 at two sites on Mars. pressed ahead with two Mars team did not know whether the the rising sun in order to maximize Exploration Rovers (MERs). In June solar-powered rovers would retain electricity generation and to top 2003, MER A, named Spirit, and adequate power to keep working. off the batteries. All nonessential MER B, Opportunity, were ready for Of all the solar system’s rocky equipment was shut down so launch. They were about the same planets, the seasons of Mars are the that power could be diverted size as a Lunokhod rover, but were most Earth-like, due to the similar to heaters that kept the rovers’ much lighter, at around 400 lb tilts of the planets’ rotational axes. internal temperature above (180 kg). By the end of January the Martin winters are dark and bitterly –40°F (–40°C). following year, both were traveling cold, with surface temperatures across the Martian deserts, hills, falling to as low as –225°F (–143°C) Continuing mission and plains, photographing surface near the polar ice caps. The hibernation worked, and features and chemically analyzing incredibly, JPL has managed to rock samples and atmosphere. They As predicted, Martian winds extend the rover missions from sent back the most glorious vistas blew fine dust onto the solar arrays, a few days to several years. More of the Martian landscape ever seen, cutting their generating power; but than five years into its mission, enabling geologists to examine the the wind also blew the panels clean however, Spirit became bogged large-scale structures of the planet. from time to time. As winter drew down in soft soil; all attempts nearer, the JPL team searched for to free it by remote control from Spirit and Opportunity had suitable locations in which the Earth failed, and unable to move landed using the same airbag- rovers could safely hibernate. To to a winter refuge, Spirit finally and-tether system as Sojourner. do this, they used a 3-D viewer lost power 10 months later. It Like Sojourner, both relied on built from the images taken from had traveled 4.8 miles (7.73 km). solar panels, but the new rovers the rover’s stereoscopic cameras. Opportunity, meanwhile, has ❯❯ were built as self-contained units, They chose steep slopes that faced able to wander far from their landers. Each vehicle’s six wheels were attached to a rocking mechanism, which made it possible for the rovers to keep at least two wheels on the ground as they crossed rugged terrain. The software offered a degree of autonomy so that the rovers could respond to unpredictable events, such as a sudden dust storm, without needing to wait for instructions from Earth. Low expectations Nevertheless, expectations for these rovers were low. JPL expected that they would cover about 2,000 ft (600 m) and last for 90 Martian sols (equivalent to about 90 Earth days). During the Martian winter, however, the

324 EXPLORING MARS avoided mishap and continues to vaporized samples of ground rock to In the “Kimberley” formation operate. In 2014, it beat Lunokhod reveal their chemicals. In addition, on Mars, photographed by Curiosity, 2’s distance record, and by August the rover monitored radiation levels strata indicate a flow of water. In the 2015 it had completed the marathon to see whether the planet would be distance is Mount Sharp, named after distance of 26.4 miles (42.45 km). safe for future human colonization. US geologist Robert P. Sharp in 2012. This was no mean feat on a planet located some hundreds of millions Considerably larger than by the sheer distance from Earth) of miles from Earth. previous rovers, Curiosity was was 14 minutes, and the journey delivered to Mars in an unusual through the atmosphere to the Curiosity needed way. During the landing phase of surface would take just seven—all Spirit and Opportunity were the mission, the radio delay (caused on autopilot (not remotely controlled equipped with the latest detectors; from Earth). This created “seven including a microscope for imaging The Seven Minutes of Terror minutes of terror”: the engineers mineral structures and a grinding has turned into the Seven on Earth knew that by the time a tool for accessing samples from Minutes of Triumph. signal arrived informing them that the interiors of rocks. John Grunsfeld Curiosity had entered the Martian atmosphere, the rover would However, Curiosity, the next NASA associate administrator already have been on the ground rover to arrive on the planet in for seven minutes—and would be August 2012, carried instruments operational or smashed to pieces. that not only studied the geology of Mars but also looked for Safe landing biosignatures—the organic As Curiosity’s landing craft moved substances that would indicate through the upper atmosphere, whether Mars once harbored life. its heat shield glowed with heat, These included the SAM or Sample while rockets adjusted the descent Analysis at Mars device, which

THE TRIUMPH OF TECHNOLOGY 325 speed to reach the Gale Crater, an be detached and blasted clear of the ExoMars ancient crater caused by a massive area so that its eventual impact did meteorite impact. A parachute not upset any future exploration. In 2020, the European Space slowed the craft to about 200 mph Agency, in collaboration with (320 km/h), but this was still too Having survived the landing, the Russian space agency, fast for a landing. It continued to Curiosity signaled to Earth that Roscosmos, will launch its slow its descent over a flat region it had arrived safely. Curiosity’s first Mars rover, ExoMars of the crater, avoiding the 20,000-ft power supply is expected to last (Exobiology on Mars), with (6,000-m) mountain at its center. at least 14 years, and the initial the goal of landing on Mars The craft reached about 60 ft two-year mission has now been the following year. In addition (20 m) above the surface and then extended indefinitely. So far, it has to looking for signs of alien life, had to hover, since going too low measured radiation levels, revealing the solar-powered rover will would create a dust cloud that that it may be possible for humans carry a ground-penetrating might wreck its instruments. The to survive on Mars; discovered an radar that will look deep rover was finally delivered to the ancient stream bed, suggesting a into Martian rocks to find surface via a rocket-powered past presence of water and perhaps groundwater. The ExoMars hovering platform called a sky even life; and found many of the key rover will communicate with crane. The sky crane then had to elements for life, including nitrogen, Earth via the ExoMars Trace oxygen, hydrogen, and carbon. ■ Gas Orbiter, which was launched in 2016. This system Distances traveled by extraterrestrial rovers will limit data transfer to twice a day. The rover is Lunokhod 1 designed to drive by itself; 1970–71 its control software will build moon: 6.5 miles a virtual model of the terrain (10.5 km) and navigate through that. Apollo 17 Rover The rover software was taught Dec. 1972 how to drive in Stevenage, moon: 22.2 miles England, at a mockup of the (35.74 km) Martian surface called the Lunokhod 2 Mars Yard (above). Jan.–Jun. 1973 moon: 24.2 miles The ExoMars rover is (39 km) expected to operate for at Sojourner least seven months and to Jul.–Sep. 1997 travel 2.5 miles (4 km) across Mars: 0.06 miles the Martian surface. It will be (0.1 km) delivered to the surface by a Curiosity robotic platform that will then 2011–present remain in place to study the Mars: 8.1 miles area around the landing site. (13.1 km) Spirit 2004–2010 Mars: 4.8 miles (7.7 km) Opportunity 2004–present Mars: 26.6 miles (42.8 km) DISTANCE IN MILES 0 6 12 18 24

326 ETYHEE OBNIGTGHEESTSKY LOOKING FARTHER INTO SPACE IN CONTEXT D espite its name, the ESO, Telescope, the new technology or European Southern being adaptive optics that reduce KEY DEVELOPMENT Observatory, is located the blurring effect on images European Extremely in northern Chile, a region of dry caused by the turbulence of the Large Telescope (2014–) desert and high mountains ideal atmosphere. In 1999, it opened for ground-based astronomy. its Very Large Telescope, which BEFORE This collaborative organization comprises four 27-ft (8.2-m) 1610 Galileo Galilei makes of 15 European countries, along reflecting telescopes that can be the first recorded astronomical with Brazil and Chile, has been used together. The Atacama Large observations using a telescope. pushing the limits of astronomy Millimeter Array, a vast radio for more than 50 years. telescope with 66 antennae, then 1668 Isaac Newton makes the became operational in 2013. This first usable reflecting telescope. Big telescopes is the largest ESO program to date, The ESO uses literal names for and the largest ground-based 1946 Lyman Spitzer Jr. its telescopes. In 1989, it began astronomical project of all time. suggests putting telescopes operating the New Technology In 2014, however, the ESO received in space to avoid Earth’s atmospheric interference. European Southern Observatory 1990 The Hubble Space Formed in 1962, the ESO today Observatory, an ultra-modern Telescope is launched. has 17 member countries: science center in the remote Austria, Belgium, the Czech desert. The observatory’s AFTER Republic, Denmark, Finland, subterranean living quarters 2015 Construction begins in France, Germany, Italy, the were used as a Bond villain’s lair Chile on the US-led 72-ft (22-m) Netherlands, Poland, Portugal, in the 2008 movie Quantum of Giant Magellan Telescope. Spain, Sweden, Switzerland, and Solace. The site’s new Extremely the UK, with Chile and Brazil. Large Telescope is costing 2016 LIGO detects the It is located in the Atacama $1.1 billion (€1 billion) to build. gravitational waves of objects Desert of Chile, chosen for its The ESO opted for this project in space. clear, moisture-free skies and after rejecting the far costlier the absence of light pollution. OWL (Overwhelmingly Large 2018 The James Webb The ESO’s headquarters is Telescope), the proposed design Space Telescope will become near Munich, Germany, but of which had a 330-ft (100-m) the largest telescope ever its working base is the Paranal wide primary mirror. launched into space.

THE TRIUMPH OF TECHNOLOGY 327 See also: Galileo’s telescope 56–63 ■ Gravitational theory 66–73 ■ Space telescopes 188–95 ■ Studying distant stars 304–05 The E-ELT’s dome is shown opening as the sun sets over the desert in this artist’s impression. The completed structure will be 256 ft (78 m) high. funding for the European Extremely artificial “star,” which is created can ripple and warp in real time Large Telescope (E-ELT). When by firing a laser into the sky. M4 to counteract any atmospheric completed in 2024, this will be can alter its shape 1,000 times a distortions. Finally, M5 directs the largest optical telescope ever second using 8,000 pistons housed the image into the camera. built, with a resolution 15 times underneath. In other words, the 798 sharper than the Hubble Space segments of this astonishing mirror The E-ELT will pick up a Telescope (pp.172–77). narrower band of the spectrum than space telescopes, but it can Giant mirror do so on a much larger scale. As The E-ELT has an unusual five- a result, the E-ELT will be able mirror design housed inside a to see exoplanets, protoplanetary dome half the size of a football discs (including their chemistry), stadium. The primary mirror (M1), black holes, and the first galaxies which collects the visible light in greater detail than ever before. ■ (and near infrared) is built from 798 hexagonal segments that are Secondary Fourth 4 ft 10 in (1.45 m) wide. Together mirror (M2) mirror (M4) they will make a mirror that is 129 ft (39.3 m) across. In contrast, the Fifth Third Hubble’s primary mirror is just mirror mirror 7 ft 11 in (2.4 m) wide; even the (M3) E-ELT’s secondary mirror (M2) is (M5) larger than that, at 13 ft 10 in (4.2 m). Primary The shape of M1 can be fine- mirror tuned to account for distortions (M1) caused by temperature changes, and by the gravitational effect as At the heart of the E-ELT’s complex arrangement of mirrors is the huge the telescope swings into different dish of the primary mirror. It will gather 13 times more light than the largest positions. M2 directs the light from existing optical telescopes, and will be aided by six laser guide star units. M1 through a hole in the fourth mirror (M4) onto the third mirror (M3). From there light is reflected back onto M4, the adaptive optics mirror, which greatly reduces atmospheric blurring of the image. M4 follows the twinkling of an

328 IN CONTEXT RSTHIPPARPCOLEUETGSIHME KEY ORGANISATION LIGO (2016)  GRAVITATIONAL WAVES BEFORE 1687 Isaac Newton formulates the universal law of gravitation, which sees gravity as a force between masses. 1915 Albert Einstein presents the general theory of relativity, which explains gravity as the distortion of spacetime by mass, predicting the existence of gravitational waves. 1960 American physicist Joseph Weber attempts to measure gravitational waves. 1984 Rai Weiss and Kip Thorne found LIGO. AFTER 2034 eLISA is scheduled to search for gravitational waves using three spacecraft in heliocentric orbits, between which lasers will be fired. I n 1916, as he worked on his theory of relativity, Albert Einstein predicted that, as a mass moved, its gravity would cause ripples in the fabric of spacetime. Every mass would do this, although larger masses would make bigger waves, in the same way that a pebble dropped in a pond makes an ever- increasing circle of ripples, while a meteor impacting the ocean creates tsunami-sized waves. In 2016, 100 years after Einstein’s predictions, a collaboration between scientists working under the name LIGO announced that they had discovered these ripples, or gravitational waves. Their

THE TRIUMPH OF TECHNOLOGY 329 See also: Gravitational theory 66–73 ■ The theory of relativity 146–53 Within a period of 20 milliseconds, the two black holes LIGO had detected increased their orbital speed from 30 times a second to 250 times a second before colliding. decades-long search had revealed space is doing: the speed of light. by the mass of objects curving the gravitational equivalent of Light behaves like a wave, but it the space around them. What is tsunamis created by two black does not require a medium through understood as the “pull of gravity” holes spiraling around each which to travel. Instead, light is a small mass appearing to alter other and then colliding. (and any kind of electromagnetic its motion and “fall” toward a larger radiation) is an oscillation of an mass as it encounters a region of It is hoped that the discovery electromagnetic field: in other warped space. of gravitational waves will provide words, light is a disturbance in a new way of observing the a field permeating all of space. All masses are in motion— universe. Instead of using light planets, stars, even galaxies—and or other electromagnetic radiation, Gravitational waves can be as they move, they leave a trail of astronomers are hoping to map understood as disturbances in the gravitational disturbances in their the universe by the gravitational gravitational field that permeates wake. Gravity waves propagate in effects of its contents. While the universe. Einstein described a comparable way to sound waves, radiation is obscured in many ways, how these disturbances are caused by distorting the medium through including by the opaque plasma which they travel. In the case of the early universe up to 380,000 of sound waves, that medium is years after the Big Bang, gravitational made of molecules, which are made waves pass through everything. to oscillate. In the case of gravity, This means that gravitational the medium is spacetime, the very astronomy could see back to the fabric of the universe. Einstein very beginning of time, a trillionth predicted that the speed of gravity ❯❯ of a second after the Big Bang. Relativity reveals that gravity is the warping of spacetime by mass. Wave behaviors Moving objects create ripples through LIGO stands for Laser Interferometer spacetime, or gravitational waves. Gravitational-Wave Observatory. It is a remarkable set of instruments Gravitational waves can Gravitational waves for measuring expansions and be detected by measuring let astronomers see contractions in space itself. This farther into space is no easy task. A ruler cannot do it the expansion and because, as space changes in size, compression of spacetime. than ever before. so does the ruler, so the observer measures no change at all. LIGO succeeded using the benchmark that remains constant whatever

330 GRAVITATIONAL WAVES would be the same as the speed With no gravitational waves, LIGO’s light waves cancel one of light, and that the ripples in another out when they are recombined. Gravitational waves stretch spacetime would move outward one tube while compressing the other, so that the waves are no in all directions. The intensity of longer perfectly aligned, and a signal is produced. these ripples diminishes rapidly with distance (by a square of the Normal Gravitational distance), so detecting a distinct situation wave detection gravity wave from a known object far out in space would require a very powerful source of waves and a very sensitive instrument. Laser-guided No signal Signal As its name suggests, LIGO employs a technique called laser out, disappearing completely. half a wavelength farther than interferometry. This makes use LIGO’s source of waves is a laser, the other (a difference of a few of a property of waves called which is a light beam that contains hundred billionths of a meter). interference. When two waves a single color, or wavelength, When the beams meet each other meet, they interfere with one of light. In addition, the light in again, they are exactly out of phase another to create a single wave. a laser beam is coherent, which as they interfere, and promptly How they do this depends on means that its oscillations are all disappear—unless a gravitational their phase—the relative timing perfectly in time. Such beams wave has passed through space of their oscillations. If the waves can be made to interfere with while the beams were traveling. are exactly in phase—rising and one another in very precise ways. If present, a gravitational wave falling perfectly in sync—they would stretch one of the laser will interfere constructively, The laser beam is split in two tracks and compress the other, so merging to create a wave with and the resulting beams are sent the beams would end up traveling double the intensity. By contrast, off perpendicular to one another. slightly altered distances. if the waves are exactly out of They both hit a mirror and bounce phase—one rising as the other straight back to the starting point. Noise filter falls—the interference will be The distance traveled by each The laser beams are split and sent destructive. The two waves will beam is very precisely controlled on a 695-mile (1,120-km) journey up merge and cancel one another so that one has to travel exactly and down LIGO’s 2.5-mile (4-km) long arms before being recombined. Rai Weiss and Kip Thorne This gives LIGO the sensitivity to detect minute perturbations in space LIGO is a collaboration between by LIGO, working from the that add up to a few thousandths Caltech and MIT, and also initial ideas of Joseph Weber, of the width of a proton. With the shares its data with a similar one of the inventors of the laser. distances put very slightly out of experiment called Virgo, which In 1984, Weiss cofounded LIGO sync, the interfering beams would is running in France and Poland. with Thorne, a counterpart at no longer cancel each other out. Hundreds of researchers have Caltech, who is a leading expert Instead, they would create a contributed to the discovery of on the theory of relativity. LIGO flickering pattern of light, perhaps gravitational waves. However, is the most expensive science indicating a gravity wave passing there are two people, both project ever funded by the US through LIGO’s corner of space. Americans, who stand out government, with a current cost among them all: Rainer “Rai” of $1.1 billion. After 32 years of The difficulty was that such Weiss (1932–) and Kip Thorne trying, in 2016 Weiss and Thorne a sensitive detector was prone to (1940–). In 1967, while at MIT, announced their discovery of distortions from the frequent seismic Weiss developed the laser gravitational waves at a news waves that run through Earth’s interferometry technique used conference in Washington, D.C. surface. To be sure that a laser flicker

THE TRIUMPH OF TECHNOLOGY 331 LIGO’s precision instruments must Colliding black holes the sun. Lasers will be fired be kept completely clean. Maintaining On September 14, 2015, at 9:50:45 between the spacecraft, making the purity of the laser beams is one GMT, two black holes a billion light- a laser track 2 million miles of the project’s biggest challenges. years away collided and unleashed (3 million km) long that is many huge warps in the fabric of space. times more sensitive to was not an earth tremor, two In fact, this event occurred a billion gravitational waves than LIGO. identical detectors were built at years ago but it had taken that long opposite ends of the United States: for the ripples they had released The discovery of gravitational one in Louisiana, the other in to reach Earth—where they were waves has the potential to transform Washington state. Only signals detected by both LIGO detectors. astronomers’ view of the universe. registering on both detectors were The researchers took another few The patterns in the fluctuations gravitational waves (the signals months to check their result and in the light signals from LIGO and are in fact 10 milliseconds apart— went public in February 2016. future projects will produce new the time it takes for light, and information, providing a detailed gravitational waves, to travel from The search is now on for more map of mass across the universe. ■ Louisiana to Washington). Ligo gravitational waves, and the best operated from 2002–2010 with no place to do it is from space. In Gravitational waves will success, then started up again in December 2015, the spacecraft bring us exquisitely accurate 2015 with enhanced sensitivity. LISA Pathfinder was launched. maps of black holes—maps It is headed to an orbit at L1, which is a gravitationally stable position of their spacetime. between the sun and Earth. Kip Thorne There, the spacecraft will test laser interferometry instruments in space, in the hope that they can be used in an ambitious experiment called eLISA (evolved Laser Interferometer Space Antenna). Provisionally scheduled for 2034, eLISA will use three spacecraft triangulated around Mirror LIGO splits one beam of laser light and sends beams Mirror down two tubes at 90° to each other. To prevent unwanted interference, the tubes are vacuums at one trillionth of the pressure of Earth’s atmosphere. LIGO also has to make adjustments to allow for the tidal pull of the sun and the moon. Beam splitter 2.5-mile (4-km) tube 2.5-mile (4-km) tube Laser source Light detector

DIRECTO

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334 DIRECTORY F or a field of enquiry as broad as astronomy, there has not been room to include every significant scientist as a main entry in this book. The following pages list astronomers who have also made important contributions across time, from the 7th century BCE to the present day. In its early stages, astronomy usually involved individuals or small groups making observations and calculations. Modern high-tech “big astronomy,” meanwhile, often requires large-scale collaborations of hundreds or thousands of scientists. Whether they are booking time for an experiment at a particle accelerator or requesting that a space telescope be pointed in a particular direction, today’s astronomers form part of a huge community developing the big ideas of tomorrow. ANAXIMANDER OF MILETUS the circumference of Earth vernal equinoxes), and the lunar by comparing the angle of the month. He used his calculations to 610–546 BCE noon shadow at midsummer in predict four solar eclipses correctly. Alexandria with that in Syene Zu measured the length of Jupiter’s Greek philosopher Anaximander (present-day Aswan). He knew the year as 11.858 Earth years, which is provided one of the earliest distance between the two locations, less than 0.1 percent away from the attempts at a rational explanation and his measurement allowed him current accepted figure. of the universe. He speculated that to figure out the proportion of the See also: The solar year 28–29 the celestial bodies made full circles entire circumference that this around Earth, which led him to the represented. He also produced AL-BATTANI conclusion that Earth must float an accurate measurement of Earth’s freely and unsupported in space. He axial tilt, measured the distances c.858–929 also stated that celestial bodies lie to the sun and the moon, introduced behind one another, meaning that the leap day to correct the length Arab astronomer and there was depth to the universe— of the year, and produced one of mathematician Al-Battani made the first recorded conception of the the first ever maps of the world. accurate observations to refine idea of “space.” Anaximander placed See also: Consolidating the figures for the length of the the celestial bodies in the wrong knowledge 24–25 year, the inclination of the ecliptic, order, however, believing that the and the precession of the equinoxes. stars were nearest to Earth, followed ZU CHONGZHI He developed trigonometric by the moon, and then the sun. methods to improve on Ptolemy’s See also: The geocentric model 20 429–500 CE calculations, and showed that the distance of the sun from Earth ERATOSTHENES Tasked with producing a new varies over time. Al-Battani’s most calendar by the Emperor Xiaowu, influential work was a compilation c.276–c.194 BCE Chinese mathematician Zu of astronomical tables, which Chongzhi made highly accurate was translated into Latin in the The third chief librarian at the measurements of the lengths of 12th century and was a major famous Library of Alexandria, the sidereal year (Earth’s rotation influence on Copernicus. Greek scholar Eratosthenes period measured relative to the See also: Consolidating knowledge made major contributions to the background stars), the tropical year 24–25 ■ The Copernican model field of geography. He measured (the period between successive 32–39

DIRECTORY 335 IBN AL-HAYTHAM Although he made and used project to calculate the time of day telescopes, he preferred to map using the eclipses of the moons c.965–1040 star positions with just a sextant of Jupiter, a method first proposed and the naked eye, making him by Galileo to solve the problem of Also known by his Latinized name the last major astronomer to do so. measuring longitude at sea. Over Alhazen, Ibn al-Haytham worked at Hevelius’s second wife, Elisabetha, a number of years, Rømer carefully the court of the Fatimid Caliphate whom he married in 1663, helped timed the eclipses of the moon Io in Cairo. A pioneer of the scientific him to compile a catalog of and found that their duration varied method, whereby hypotheses are more than 1,500 stars, which she depending on whether Earth was tested by experiment, al-Haytham completed and published following moving toward Jupiter or away from wrote a work popularizing his death. A tireless and skilled it. He reasoned that this variation Ptolemy’s Almagest and, later, a observer in her own right, was due to a difference in the time it book casting doubts on aspects Elisabetha was one of the first took the light from Io to reach Earth, of Ptolemy’s system. notable female astronomers. and estimated that light takes See also: Consolidating See also: The Tychonic model 22 minutes to travel a distance equal knowledge 24–25 44–47 to the diameter of Earth’s orbit of the sun. This gave the speed of light ROBERT GROSSETESTE CHRISTIAAN HUYGENS as 140,000 miles/s (220,000 km/s), about 75 percent of its true value. c.1175–1253 1629–1695 Rømer’s finding that light has a finite speed was confirmed in 1726, English bishop Robert Grosseteste Dutch mathematician and when James Bradley explained the wrote treatises concerning optics, astronomer Christiaan Huygens phenomenon of stellar aberration mathematics, and astronomy. He was fascinated by Saturn and the in terms of light speed. translated Greek and Arabic texts strange “handles” that telescopes See also: Stellar aberration 78 into Latin, introducing the ideas of revealed to protrude from either side Aristotle and Ptolemy into medieval of it. With his brother Constantijn, JOHN MICHELL European thought. In his work De he constructed a powerful telescope luce (On light), Grosseteste made with improved lenses through which 1724–1793 an early attempt to describe the to study the planet. Huygens was entire universe using a single set of the first to describe the true shape English clergyman John Michell mathematical laws. He called light of Saturn’s rings, explaining that studied a wide range of scientific the first form of existence, which, he they were thin and flat, and tilted fields, including seismology, said, allowed the universe to spread at an angle of 20 degrees to the magnetism, and gravity. He designed out in all directions, in a description plane of the planet’s orbit. He the torsion balance, which his reminiscent of the Big Bang theory. published his findings in 1659 in friend Henry Cavendish later used See also: The geocentric model the book Systema Saturnium. Four to measure the strength of gravity. 20 ■ Consolidating knowledge 24–25 years earlier, he had discovered Michell was also the first person to Titan, Saturn’s largest moon. propose that an object might be so JOHANNES HEVELIUS See also: Observing Saturn’s massive that light would be unable rings 65 to escape its gravitational pull. He 1611–1687 calculated that a star 500 times the OLE RØMER size of the sun would be such an ELISABETHA HEVELIUS object, which he called a “dark star.” 1644–1710 Michell’s idea was largely forgotten 1647–1693 until the 20th century, when Working at the Paris Observatory, astronomers started to take the From an observatory he built on Danish astronomer Ole Rømer concept of black holes seriously. top of his house, Polish astronomer demonstrated that light has a finite See also: Curves in spacetime Johannes Hevelius made detailed speed. Rømer was working on a 154–55 ■ Hawking radiation 255 maps of the surface of the moon.

336 DIRECTORY JOSEPH-LOUIS LAGRANGE BENJAMIN APTHORP GOULD parts of the sun were rotating at different speeds. 1736–1813 1824–1896 See also: Galileo’s telescope 56–63 ■ The surface of the sun 103 French–Italian mathematician and A child prodigy, American Benjamin astronomer Joseph-Louis Lagrange Apthorp Gould graduated early from ISAAC ROBERTS studied celestial mechanics and Harvard University before moving the effects of gravity. He explored to Germany to study under the 1829–1904 mathematically the ways in which renowned mathematician Friedrich the gravitational pulls within a Gauss in 1845. In Europe, he earneda In the 1880s, British amateur system of three bodies, such as the Ph.D. in astronomy—the first astronomer Isaac Roberts made sun, Earth, and the moon, combine American to receive a doctorate in important advances in the field with one another. His work led to the the subject. He returned to the US in of astrophotography, enabling discovery of positions with stable 1849 determined to raise the profile photographs of the night sky to orbits for a small body orbiting two of American astronomy. To this reveal structures invisible to the larger ones, now called Lagrange end, he founded The Astronomical naked eye for the first time. Roberts points. Space telescopes are often Journal to publish research from the developed an instrument that placed near Lagrange points for their United States; the journal continues allowed very long exposure times, orbits around Earth and the sun. to this day. Between 1868 and 1885, and thus the collection of more light. See also: Gravitational theory Gould worked in Argentina, where He kept the telescope pointing at 66–73 ■ Studying distant stars he founded the National Observatory exactly the same point in the sky by 304–05 in Córdoba. He also helped to adjusting it to compensate for the set up the Argentine National rotation of Earth. Roberts’ most JEAN BAPTISTE JOSEPH Weather Service. Gould produced famous image is an 1888 photograph DELAMBRE a comprehensive catalog of of the Andromeda nebula, now the bright stars visible from the known to be a galaxy, which 1736–1813 southern hemisphere, which revealed its spiral structure in he published in 1879 as the unprecedented detail. A leading figure in scientific circles Uranometria Argentina. See also: Astrophotography during the French Revolution, in 118–19 1792 Delambre was tasked with RICHARD CARRINGTON measuring the length of the arc of the HENRY DRAPER meridian from Dunkirk to Barcelona. 1826–1875 This was to refine the new metric 1837–1882 system, which defined the meter as British amateur astronomer 1/10,000,000 of the distance from Richard Carrington carried out A pioneer of astrophotography, the North Pole to the equator. He careful observations of the sun medical doctor Henry Draper completed the task in 1798. From over the course of many years. resigned as dean of medicine at 1804, Delambre served as the In 1859, he was the first person to New York University in 1873 to director of the prestigious Paris observe a solar flare—a magnetic devote himself to astronomy. With Observatory. His astronomical explosion on the surface of the the assistance of his wife, Anna work included the production sun that causes a surge of visible Mary, Draper photographed the of accurate tables showing the light. The flare was followed by transit of Venus in 1874, was positions of Jupiter’s moons. In disruption to worldwide telegraph the first to capture the Orion nebula 1809, he estimated that light from systems, and Carrington suggested on camera in 1880, and was also the sun takes 8 minutes 12 seconds that such solar activity might have the first to take a wide-angled to reach Earth (the figure is now an electrical effect on Earth. photograph of a comet’s tail in measured at 8 minutes 20 seconds). In 1863, through his records of 1881. He developed new techniques See also: Gravitational the movements of sunspots, he for astrophotography, but died of disturbances 92–93 demonstrated that different pleurisy in 1882, a few years before

DIRECTORY 337 photography began to be taken sunspots uncovered a correlation HEBER D. CURTIS seriously by astronomers as a means between their number and Earth’s of discovery. After his death, his wife climate. This led them to discover 1872–1942 created a foundation in his name, a period of reduced solar activity which funded the Henry Draper between 1645 and 1715, now called American classics professor Heber Catalogue, a huge photographic the Maunder Minimum, which Doust Curtis switched to astronomy survey of the stars carried out by coincided with lower-than-average in 1900 when he became a volunteer Edward C. Pickering and his team temperatures in Europe. When the observer for the Lick Observatory in of female astronomers. ban on women at the society was California. After receiving his Ph.D. See also: The star catalog lifted in 1916, Annie Maunder in astronomy in 1902, Curtis enjoyed 120–21 ■ The characteristics of was elected a Fellow of the Royal a long association with the Lick the stars 122–27 Astronomical Society, after Observatory, carrying out a detailed which her observations were survey of the known nebulae, which JACOBUS KAPTEYN published under her own name. he completed in 1918. In 1920, he Prior to that, much of her work took part in the “Great Debate” with 1851–1922 had appeared in papers under fellow astronomer Harlow Shapley her husband’s name. at the Smithsonian museum. Curtis Using photographic plates supplied See also: The surface of the sun argued that distant nebulae were to him from South Africa by David 103 ■ The properties of sunspots 129 separate galaxies far from the Milky Gill, Dutch astronomer Jacobus Way, while Shapley asserted that Kapteyn cataloged more than E. E. BARNARD they lay within it. 450,000 southern stars. After See also: Spiral galaxies 156–61 ■ grouping stars in different parts 1857–1923 Beyond the Milky Way 172–77 of the galaxy and measuring their magnitudes, radial velocities, and US astronomer Edward Emerson JAMES JEANS proper motions, Kapteyn carried out Barnard was a renowned observer, vast statistical analyzes that revealed who discovered about 30 new 1877–1946 the phenomenon of star streaming— comets and numerous nebulae. which shows how the motions of In 1892, Barnard discovered British mathematician James Jeans stars are not random, but grouped a fifth moon around Jupiter, called worked on a variety of theoretical together in two opposite directions. Amalthea, which was to be the problems relating to astrophysics. In This was the first definitive evidence last moon to be discovered through 1902, he calculated the conditions that the Milky Way galaxy is rotating. visual observation rather than under which a cloud of interstellar See also: Astrophotography through the study of photographic gas becomes unstable and collapses 118–19 plates. Himself a pioneer of astro- to form a new star. In developing his photography, Barnard produced theory of gases in 1916, he explained EDWARD WALTER MAUNDER a series of stunning long-exposure how gas atoms can gradually escape photographs of the Milky Way, from a planet’s atmosphere over time. 1851–1928 which was published posthumously In later life, Jeans devoted his time to in 1927 as the Atlas of Selected writing and became well-known for ANNIE SCOTT DILL Regions of the Milky Way. Barnard’s his nine popular books, including MAUNDER star is named after him; in 1916, he Through Space and Time and The discovered that this faint red dwarf Stars in Their Courses. He promoted 1868–1947 has the largest known proper motion an idealist philosophy that saw (rate at which a star changes its both mind and matter as central to British husband and wife team position on the celestial sphere) understanding the universe, which Edward Walter Maunder and of all known stars. he described as “nearer to a great Annie Maunder (née Scott Dill) See also: Galileo’s telescope thought than to a great machine.” collaborated at the Greenwich 56–63 ■ Astrophotography See also: Inside giant molecular Royal Observatory in the study 118–19 clouds 276–79 of the sun. Their investigations of

338 DIRECTORY ERNST ÖPIK status of dwarf planet. Following after the end of World War II. To his discovery, Tombaugh earned a conduct further radio investigations 1893–1985 degree and pursued a career as in clear atmospheric conditions, a professional astronomer. in 1954 Reber moved to Tasmania, Estonian astrophysicist Ernst See also: Spiral galaxies 156–61 ■ where he remained for the rest Öpik obtained his doctorate at the Studying Pluto 314–17 of his life. University of Tartu, Estonia, where See also: Radio astronomy 179 he worked from 1921 to 1944, VICTOR AMBARTSUMIAN specializing in the study of minor IOSIF SHKLOVSKY objects such as asteroids, comets, 1908–1996 and meteors. In 1922, he estimated 1916–1985 the distance of the Andromeda Soviet–Armenian astronomer Victor galaxy using a new method based Ambartsumian was a founding In 1962, Soviet astrophysicist on the galaxy’s speed of rotation. figure in the field of theoretical Iosif Shklovsky wrote a popular This method is still used today. astrophysics, contributing to book examining the possibility Öpik also suggested that comets theories of star formation and of extraterrestrial life, which was originated from a cloud beyond galactic evolution. He was one of republished four years later in an Pluto, now known commonly as the first people to suggest that young expanded edition, co-authored by the Oort cloud, but sometimes stars formed from protostars. In Carl Sagan, as Intelligent Life in referred to as the Öpik–Oort cloud. 1946, he organized the construction the Universe. In this later edition, As the Red Army approached of the Byurakan Observatory in paragraphs by the two authors Estonia in 1944, Öpik fled into Armenia, where he was the director are alternated with one another, exile, eventually settling in until 1988. A popular lecturer with as Sagan provides a commentary Northern Ireland, where he took a colorful and engaging style, and expansion on Shklovsky’s a position at Armagh Observatory. Ambartsumian served as the original points. Many of the latter’s See also: The Oort cloud 206 president of the International ideas were highly speculative, Astronomical Union from 1961–64, including a suggestion that an CLYDE TOMBAUGH and hosted several conferences on observed acceleration of Mars’s the search for extraterrestrial life. moon Phobos was due to the fact 1906–1997 See also: Dense molecular clouds that it was a hollow artificial 200–01 ■ Inside giant molecular structure, a monument to a long- In the late 1920s, the Lowell clouds 276–79 gone Martian civilization. Observatory in Arizona embarked See also: Life on other planets upon a systematic search for a GROTE REBER 228–35 planet believed to be causing perturbations to the orbit of 1911–2002 MARTIN RYLE Uranus. To carry out the work, the director Vesto Slipher hired the In 1937, American radio engineer 1918–1984 young amateur astronomer Clyde Grote Reber built his own radio Tombaugh, who had impressed him telescope in his backyard after Like many pioneer radio with drawings of Jupiter and Mars hearing of Karl Jansky’s discovery astronomers, Briton Martin Ryle made using a homemade telescope. of galactic radio waves. Over started his career developing radar After 10 months examining the next few years, Reber was technology during World War II. photographs, on February 18, 1930, effectively the only radio astronomer Subsequently, he joined the Tombaugh discovered an object in the world, conducting the Cavendish Radio Astronomy Group orbiting the sun beyond Neptune. first radio survey of the sky and in Cambridge, where he worked Named Pluto after the Roman god publishing his results in astronomy alongside Antony Hewish and of the underworld, it was initially and engineering journals. Reber’s Jocelyn Bell Burnell, developing classified as the ninth planet, but work was to form the basis for the new techniques in radio astronomy has since been demoted to the development of radio astronomy and producing a number of catalogs

DIRECTORY 339 of radio sources. Deeply affected Penrose has proposed a theory of a life to develop. Since 1986, Carter by his experiences of war, Ryle cyclic cosmology, in which the heat has been the director of research devoted his final years to the death (end state) of one universe at the Paris–Meudon Observatory. promotion of the peaceful use produces the conditions for the He has also made contributions of science, warning against the Big Bang of another universe. to understanding the properties dangers of nuclear weapons and Penrose has also produced a of black holes. power, and advocating research series of popular science books See also: Life on other planets into alternative energy. in which he explains the physics 228–35 ■ Hawking radiation 255 See also: Radio astronomy 179 ■ of the universe and suggests Quasars and pulsars 236–39 novel explanations for the origins JILL TARTER of consciousness. HALTON ARP See also: Curves in spacetime 1944– 154–55 ■ Hawking radiation 255 1927–2013 As director of the Center for SETI SHIV S. KUMAR Research in California, Jill Tarter A staff astronomer at the Mount was a leading figure in the search Wilson Observatory in California 1939– for extra-terrestrial life for more for nearly 30 years, Halton Arp than 30 years, lecturing widely on gained a reputation as a skilled Indian-born astronomer Shiv S. the subject before her retirement in observer. In 1966, he produced Kumar earned a doctorate in 2012. In 1975, she coined the term his Atlas of Peculiar Galaxies, astronomy at the University of “brown dwarf” for the type of star, which cataloged, for the first Michigan and has made his career discovered by Shiv S. Kumar, that time, hundreds of odd structures in the United States, working on is not massive enough to sustain that had been seen in nearby theoretical problems concerning nuclear fusion. Carl Sagan based galaxies. Today it is known that matters including the origin of the the protagonist in his novel and many of these features are the solar system, the development of film Contact on Tarter. result of galaxies colliding. Later life in the universe, and exoplanets. See also: Life on other planets in his career, Arp found himself In 1962, Kumar predicted the 228–35 professionally marginalized when existence of low-mass stars that he cast doubt on the Big Bang would be too small to sustain MAX TEGMARK theory. He contended that objects nuclear fusion. Later named with very different degrees of brown dwarfs by Jill Tarter, their 1967– redshift were close to one another existence was confirmed in 1995. and not at vastly different distances. See also: Exoplanets 288–95 Swedish cosmologist Max See also: Beyond the Milky Way Tegmark’s research at MIT has 172–77 BRANDON CARTER focused on developing methods to analyze the vast amounts of ROGER PENROSE 1942– data produced by surveys of the cosmic microwave background. 1931– In 1974, Australian physicist Tegmark is a leading proponent Brandon Carter formulated the of the idea that the results of In the 1960s, British mathematician anthropic principle, which states quantum mechanics are best and physicist Roger Penrose that the universe must necessarily explained by the existence of a figured out much of the complex have certain characteristics for multiverse. He has developed the mathematics relating to the humankind to exist. That is to say mathematical universe hypothesis, curvature of spacetime around a that the physical properties of the which proposes that the universe black hole. In collaboration with universe, such as the strength of is best understood as a purely Stephen Hawking, he showed how the fundamental forces, must fall mathematical structure. matter within a black hole collapses within very narrow limits for See also: Observing the CMB into a singularity. More recently, sunlike stars capable of sustaining 280–85

340 GLOSSARY Absolute magnitude A measure Big Bang The event with which Comet A small, icy body in orbit of the intrinsic brightness of a the universe is thought to have around the sun. When a comet star. It is defined as the apparent begun, at a particular time in the approaches the sun, gas and dust magnitude of the star from a distance past, from a hot, dense initial state. evaporate from its nucleus (solid of 10 parsecs (32.6 light-years). core) to produce a cloud called Black body A theoretical, idealized a coma and one or more tails. Accretion The process by body that absorbs all the radiation which smaller particles or that falls on it, reflecting nothing. Constellation One of 88 named bodies collide and join together A black body would emit a regions on the celestial sphere, to form larger bodies. spectrum of radiation with containing an identifiable pattern a peak at a particular wavelength, of naked-eye stars. Aphelion The point on its elliptical depending on its temperature. orbit around the sun at which a Cosmic Microwave Background planet, asteroid, or comet is Black hole A region of spacetime (CMB) Faint microwave radiation farthest from the sun. surrounding a mass that is so that is detectable from all directions. dense that its gravitational pull The CMB is the oldest radiation Apparent magnitude A measure allows no mass or radiation to in the universe, emitted when the of the brightness of a star as seen escape from it. universe was 380,000 years old. from Earth. The fainter the object, Its existence was predicted by the the higher the value of its apparent Blueshift A shift in a spectrum Big Bang theory, and it was first magnitude. The faintest stars of light or other radiation toward detected in 1964. visible to the naked eye are of shorter wavelengths that occurs a magnitude 6. when the source of the light is Cosmic rays Highly energetic moving toward the observer. particles, such as electrons and Armillary sphere An instrument protons, that travel through space that models the celestial sphere. Bok globule Small, dark clouds of at close to the speed of light. At its center is Earth or the sun, cold gas and dust, within which it is around which is a framework of thought that new stars are forming. Cosmological constant A term rings representing lines of celestial that Albert Einstein added to longitude and latitude. Brown dwarf A starlike ball his general relativity equations, of gas that is not massive enough which may correspond to the dark Asteroid A small body that to sustain nuclear fusion in its core. energy that is accelerating the orbits the sun independently. expansion of the universe. Asteroids are found throughout Celestial sphere An imaginary the solar system, with the greatest sphere surrounding Earth. The Dark energy A little-understood concentration in the asteroid belt positions of stars and other celestial form of energy that exerts a repulsive between the orbits of Mars and bodies can be defined by their force, causing the expansion of the Jupiter. Their diameters range from places on this sphere if they were universe to accelerate. a few yards to 600 miles (1,000 km). imagined to be attached to it. Dark matter A form of matter that Astronomical unit (AU) Cepheid variable A pulsating does not emit radiation or interact A distance equal to the average star whose brightness increases with other matter in any way other distance between Earth and the and decreases over a regular than through the effect of its gravity. sun. 1 AU = 92,956,000 miles period. The more luminous it is, the It comprises 85 percent of all mass (149,598,000 km). longer the period of its variation. in the universe.

GLOSSARY 341 Degeneracy pressure An Equinox A twice-yearly occasion Gravitational wave A outward pressure within a when the sun is directly overhead distortion of space that travels concentrated ball of gas, such at a planet’s equator, meaning that at the speed of light, generated as a collapsed star, that is exerted day and night are of roughly equal by the acceleration of mass. due to the principle that no two duration across the entire planet. particles with mass can exist in Harvard Spectral Classification the same quantum state. Escape velocity The minimum A system first devised by the velocity an object needs to be Harvard Observatory in the late Doppler effect The change in traveling at to escape the 19th century to classify stars by frequency of radiation experienced gravitational pull of a larger the appearance of their spectra. by an observer in relative motion body such as a planet. to the source of the radiation. Heliocentric Of a system or an Event horizon A boundary orbit, treated as having the sun Dwarf planet An object in orbit around a black hole beyond at the center. around a star that is large enough to which no mass or light can have formed a spherical shape but escape its gravity. At this point, Hertzsprung–Russell diagram that has not cleared its orbital path of the escape velocity of the black A scatter diagram on which stars other material. Examples in the solar hole equals the speed of light. are plotted according to their system include Pluto and Ceres. luminosity and surface temperature. Exoplanet A planet that orbits Dwarf star Also called a main a star other than the sun. Hubble’s law The observed sequence star, a star that shines by relationship between the redshifts converting hydrogen to helium. About Fraunhofer lines Dark absorption and distances of galaxies, which 90 percent of stars are dwarf stars. lines found in the spectrum of the shows galaxies receding with sun, first identified by German a velocity proportional to their Eclipse The blocking of light Joseph von Fraunhofer in the distance. The number that from one celestial body, caused 19th century. quantifies the relationship is by another body passing between called Hubble’s constant (H0). it and an observer, or it and a light Galaxy A large collection of stars source that it reflects. and clouds of gas and dust that is Inflation A short period of rapid held together by gravity. expansion that the universe Ecliptic The apparent path along is thought to have undergone which the sun travels across the Galilean moon One of the four moments after the Big Bang. celestial sphere. It is equivalent biggest moons of Jupiter, first to the plane of Earth’s orbit. discovered in 1610 by Galileo. Ionization The process by which an atom or molecule gains or loses Electromagnetic radiation General theory of relativity electrons to gain a positive or Waves that carry energy through A theory that describes gravity negative charge. The resultant space in the form of oscillating as a warping of spacetime by charged particles are called ions. electric and magnetic disturbances. the presence of mass. Formulated The electromagnetic spectrum by Albert Einstein in 1916, Kepler’s laws of planetary ranges from short, high-energy many of its predictions, such as motion Three laws devised by gamma rays to long, low-energy gravitational waves, have now Johannes Kepler to describe the radio waves, and includes the been confirmed experimentally. shapes and speeds of the orbits visible spectrum. of the planets around the sun. Geocentric Of a system or an orbit, Electron A subatomic particle treated as having Earth at the center. Kuiper belt A region of space with negative charge. In an atom, beyond Neptune in which a large a cloud of electrons orbits a central, Gnomon The part of a sundial number of comets orbit the sun. It positively charged nucleus. that casts a shadow. is the source of short-period comets.

342 GLOSSARY Light-year (ly) A unit of distance Oort cloud Also known as the Proton A subatomic particle with that is the distance traveled by Oort–Öpik cloud. A spherical region a positive charge, made of three light in one year, equal to 5,878 at the edge of the solar system quarks. The nucleus of the element million miles (9,460 billion km). containing planetesimals and hydrogen contains a single proton. comets. It is the origin of long- Main sequence See dwarf star. period comets. Protostar A star in the early stages of its formation, comprising Messier object One of the nebulae Orbit The path of a body around a collapsing cloud that is accreting first cataloged by Charles Messier another, more massive, body. matter but in which nuclear fusion in 1781. has not yet begun. Parallax The apparent shift in Meteorite A lump of rock or position of an object due to the Pulsar A rapidly rotating neutron metal that falls from space and movement of an observer to a star. Pulsars are detected on reaches the surface of Earth in different place. Earth by their rapid, regular one piece or in many fragments. pulses of radio waves. Perihelion The point on its Nebula A cloud of gas and dust in elliptical orbit around the sun Quadrant An instrument for interstellar space. Before the 20th at which a planet, asteroid, measuring angles of up to 90°. century, any diffuse object in the or comet is closest to the sun. Ancient astronomers used sky was known as a nebula; many of quadrants to measure a star’s these are now known to be galaxies. Perturbation A change in the position on the celestial sphere. orbit of a body, caused by the Neutrino A subatomic particle gravitational influence of other Quark A fundamental subatomic with very low mass and zero orbiting bodies. Observed particle. Neutrons and protons are electric charge, which travels perturbations in the orbit of made of three quarks. at close to the speed of light. the planet Uranus led to the discovery of Neptune. Quasar Short for “quasi-stellar Neutron A subatomic particle radio source,” a compact but made of three quarks with zero Planet A non-luminous body powerful source of radiation electric charge. that orbits a star such as the sun, that is believed to be an active is large enough to be spherical galactic nucleus. Neutron star A very dense, in shape, and has cleared its compact star composed almost neighborhood of smaller objects. Radial velocity The part of the entirely of densely packed neutrons. velocity of a star or other body Neutron stars form when the core Planetesimal A small body of that is along the line of sight of a high-mass star collapses in rock or ice. The planets formed directly toward or directly a supernova explosion. from planetesimals that joined away from an observer. together by the process of accretion. Nova A star that suddenly Radio astronomy The branch of becomes thousands of times Precession A change in the astronomy that studies radiation brighter before returning to its orientation of a rotating body’s in the long radio wavelength, first original brightness over a period axis of rotation, caused by discovered to be coming from of weeks or months. the gravitational influence space in the 1930s. of neighboring bodies. Nuclear fusion A process whereby Red dwarf A cool, red, atomic nuclei join together to Proper motion The rate at which low-luminosity star. form heavier nuclei, releasing a star changes its position on the energy. Inside stars like the sun, celestial sphere. This change is Red giant A large, highly luminous this process involves the fusion caused by the star’s motion relative star. A main sequence star becomes of hydrogen atoms to make helium. to the motion of other stars. a red giant near the end of its life.

GLOSSARY 343 Redshift A shift in a spectrum Spacetime The four-dimensional Stellar parallax See parallax. of light or other radiation toward combination of the three longer wavelengths that occurs dimensions of space and one Subatomic particle One of the when the source of the light is of time. According to the theory many kinds of particle that are moving away from an observer. of relativity, space and time do smaller than atoms. These include not exist as separate entities. electrons, neutrinos, and quarks. Reflecting telescope A telescope Rather, they are intimately in which an image is formed by linked as one continuum. sunspot An area on the surface of reflecting light on a curved mirror. the sun that appears dark because Spectrum The range of the it is cooler than its surroundings. Refracting telescope A telescope wavelengths of electromagnetic sunspots are found in areas of that creates an image by bending radiation. The full spectrum concentrated magnetic field. light through a converging lens. ranges from gamma rays, with wavelengths shorter than an atom, Supernova The result of the Relativity Theories developed to radio waves, whose wavelength collapse of a star, which causes an by Albert Einstein to describe the may be many feet long. explosion that may be many billions nature of space and time. See also of times brighter than the sun. general theory of relativity. Spectroscopy The study of the spectra of objects. The spectrum Time dilation The phenomenon Satellite A small body that of a star contains information about whereby two objects moving orbits a larger one. many of its physical properties. relative to each other, or in different gravitational fields, experience Schwarzschild radius The Spiral galaxy A galaxy that a different rate of flow of time. distance from the center of a takes the shape of a central black hole to its event horizon. bulge or bar surrounded by TNO Short for Trans-Neptunian a flattened disk of stars in a Object. Any minor planet (dwarf SETI Short for Search for pattern of spiral arms. planet, asteroid, or comet) that Extra-Terrestrial Intelligence, orbits the sun at a greater average the scientific search for alien life. Standard candle A celestial body distance than Neptune (30 AU). that has a known luminosity, such Seyfert galaxy A spiral galaxy as a Cepheid variable star. These Transit The passage of a celestial with a bright, compact nucleus. allow astronomers to measure body across the face of a larger body. distances that are too large to Sidereal Relating to the stars. measure using stellar parallax. Wavelength The distance A sidereal day corresponds to between two successive peaks Earth’s rotation period measured Star A luminous body of hot gas or troughs in a wave. relative to the background stars. that generates energy through nuclear fusion. White dwarf A star with low Singularity A point of infinite luminosity but high surface density at which the known laws of Steady State theory A theory temperature, compressed by physics appear to break down. It is proposing that matter is constantly gravity to a diameter close to theorized that there is a singularity created. The theory was an attempt that of Earth. at the center of a black hole. to explain the universe’s expansion without the need for a “Big Bang.” Zodiac A band around the Solar wind A stream of fast- celestial sphere, extending 9° on moving, charged particles Stellar aberration The apparent either side of the ecliptic, through emanating from the sun that motion of a star caused by movement which the sun, moon, and planets flows out through the solar system. of an observer in a direction appear to travel. The zodiac crosses It consists mostly of electrons perpendicular to the direction the constellations that correspond and protons. to the star. to the “signs of the zodiac.”

344 INDEX Numbers in bold refer apparent magnitude 135, 136, 138 Becquerel, Henri 111, 140, 166 to a main entry Aquinas, Thomas 20 archaeology 12 Bell Burnell, Jocelyn 179, 180, 205, 40 Eridani 141, 178 Archimedes 21 218, 236–9 51 Pegasi-b (Bellerophon) 290, 291, 293 Arecibo message 233, 234 67P/Churyumov–Gerasimenko 206, 207, Aristarchus of Samos 18, 21, 34, 36, 38, 102 Bessel, Friedrich 21, 78, 83, 102, 132 Aristotle 18, 20, 21, 24, 26, 34, 35, 44–5, Bethe, Hans 166, 182–3, 196, 198, 252 308–11 1054 supernova 19 46, 48, 74, 77 BICEP2 272, 273 armillary spheres 45 A Armstrong, Neil 205, 248, 320 Big Bang 116, 148, 163, 168, 171, 177, Arp, Halton 339 absolute magnitude 135, 139, 141 Arrhenius 230 179, 182, 196, 197, 198, 199, 220, absorption lines 125–7, 128, 163 Aryabhata 19, 26 222–7, 272, 273, 277, 282–3, 284, accretion disk 221 Asphaug, Erik 186 active galactic nuclei (AGNs) 185 asteroid belt 82, 90, 91, 97, 312 300, 329 active galaxies 185, 221 asteroids 65, 72, 82, 83, 90–91, 96, 99, 308 Adams, Fred 277 Aston, Francis 182 Big Crunch 301, 303 Adams, John Couch 107 astrobiology 15 Adams, Walter 124, 138, 141, 178, 180 astrochemistry 15 Big Rip 303 adaptive optics (AO) 192 astrology 13, 25, 52 al-Battani 334 astronomy Big Splash 187 al-Sijzi 26 observations 14–15 al-Sufi, Abd al-Rahman 24, 27, 30, 87 origins of 12–13 binary stars 49, 86, 110, 214, 216, 217, Albertus Magnus 230 purpose of 14 Aldrin, Buzz 248, 320 scope of 15 294, 302 Alfonsine Tables 24 astrophotography 118–19, 120 Alfonso, Giovanni 69 astrophysics 15 Biot, Jean-Baptiste 91 Almagest (Ptolemy) 18, 19, 21, 24, 25, 27, rise of 108–41 Atacama Large Millimeter Array 259, black bodies 283–4 30, 34, 86 Alpha Centauri 102, 180 326–7 black dwarfs 127 Alpher, Ralph 116, 182, 196–7, 198, Atkinson, Robert 166, 167, 182, 183, 198 black holes 14, 82, 145, 148, 153, 154–5, atomic clocks 13 224–5, 226, 272 atomic theory 112, 114 178, 179, 181, 205, 214, 216, 217, Alvarez, Luis 212 atoms 144, 145 218–21, 239, 269 Amalthea 63 at center of Milky Way 154, 297 Ambartsumian, Victor 338 B Anaxagoras 231 colliding 329, 331 Anaximander of Miletus 18, 334 Baade, Walter 137, 140, 141, 145, discovering 254 ancient world 12–13, 18–25 180–81, 236 radiation emissions 255 Anders, Bill 247 supermassive 154, 179, 217, 221, 297 Anderson, Carl 140 Babcock, Horace 270 Andromeda galaxy/nebula 27, 87, 110, Babylonians 13, 18, 24, 25 blue dwarfs 279 Backer, Donald 236 132, 136, 137, 159–60, 161, 174, 216, Baghdad 19 blue supergiants 126 221, 270 Bahcall, John 253 antineutrinos 252 Bailey, Solon I 136 blueshift 159, 160, 270 Apianus, Petrus 76, 77 Barnard, Edward 63, 200, 337 Apollo missions 14, 186, 205, 244–9, Barringer, Daniel 212 Bode, Johann Elert 79, 85, 96, 97, 98, 99 320, 325 Bohr, Niels 112, 114 Bok, Bart 200–201, 276 Bok globules 200–201, 276, 278 Bolton, Tom 254 Bondi, Hermann 290, 300 Borman, Frank 247 Bournon, Jacques-Louis de 90 Bouvard, Alexis 106 Bowen, Ira 114 Boyle, Robert 167 Boyle’s Law 167 Bradley, James 39, 43, 78 Brahe, Tycho 20, 30, 31, 36, 39, 42, 43, 44–7, 48, 52–4, 74–5, 102, 180 Braun, Wernher von 208, 245 brown dwarfs 127, 258, 293, 294 Bruno, Giordano 42, 230 Bryson, Bill 271 Bunsen, Robert 110, 112, 113, 114 Burney, Venetia 316

INDEX 345 C CMB see cosmic microwave background Davis, Ray 252–3 COBE (Cosmic Background Explorer) Deep Impact mission 308 Caesar, Julius 28 Delambre, Jean Baptiste Joseph 83, calendars 28–9 224, 227, 282, 284–5 Callisto 62, 63 Cocconi, Giuseppe 204, 210–11, 231 93, 336 camera obscuras 49 Cohen, I Bernard 60 Delta Cephei 48, 86, 132 Cannon, Annie Jump 111, 113, 120, Coma cluster 270 Democritus 27 comets 46, 69–70, 72, 73, 110, 184, 206, density wave theory 276, 277, 278 124–7, 133, 138, 162 Dicke, Robert H 224–7 Cape Observatory (South Africa) 79, 119 287, 312 Digges, Thomas 34 carbon 199 composition of 207, 286, 308 disk galaxies 240 carbon-nitrogen-oxygen (CNO) cycle Halley’s 74–7 Dolland, John 43 landing on 306–11 Doppler, Christian 158, 159, 274 166, 183 Compton Gamma Ray Observatory 195 Doppler effect 158, 159–61, 176, 238, Carrington, Richard 336 computer technology 259 Carte du Ciel project 100, 119 Comte, Auguste 15 274 Carter, Brandon 230, 339 constellations 24, 25, 79 Doppler spectroscopy 291 Cassini, Giovanni Domenico 43, 65 Copernican principle 62, 230, 235, double-star systems see binary stars Cassini Division 65 Drake, Frank 210, 231–2, 233 Cassiopeia 45 290–91, 292 Draper, Henry 100, 110, 118, 120, 121, Cassiopeia B 45 Copernicus, Nicolaus 19, 21, 22, 23, Caterpillar Bok globule 200 124, 336–7 Cat’s Eye nebula 115 24, 26, 30, 32–9, 44, 46–7, 52, 58, Draper, John 118 Cavendish, Henry 68, 70–71 62–3, 291 Draper, Mary 121 celestial equator 22 Corot-3b 294 Draper Catalogue of Stellar Spectra 111, celestial mechanics 15, 92–3 cosmic inflation 272–3, 274, 282 Celestial Police 97–9 cosmic microwave background (CMB) 121, 124 celestial sphere 22, 25 179, 195, 196, 197, 204, 224–7, 272, dwarf galaxies 100–101 Cellarius, Andreas 36 280–85, 300–301 dwarf planets 84, 90, 96, 99, 184, 287, centaurs 312 cosmic radiation 214–17 Cepheid variables 86, 111, 120, 132–7, cosmic radio waves 58, 219 313, 314, 315 cosmic rays 111, 140, 198, 254 dwarf stars 126, 138, 139, 180 161, 174, 175, 177 cosmic wind 267 Ceres 82, 83, 90, 94–9, 315 cosmological constant 176, 177, 300, 303 E Cernan, Eugene 249, 320 cosmology 15 Cerulli, Vincenzo 117 Cowan, Clyde 252 Earth Chadwick, James 236 Crab nebula 19, 140, 237, 239 age of 186 Chaffee, Roger 247 Crabtree, William 64 atmosphere 20, 140, 190–91 Chamberlin, Thomas Chrowder 250 craters 212 composition of 187 Chandra X-ray Observatory 195, 214, cubewanos 287 distance from sun 64 Curiosity rover 259, 320, 324–5 geocentric model 18, 20, 24, 26, 34–6, 216–17, 237, 297, 301 Curtis, Heber D. 161, 174, 175, 337 Chandrasekhar, Subrahmanyan 141, Cygnus X-1 214, 218, 254 47, 62 gravity 72–3, 187 145, 154, 178, 180, 181 D life on 73, 231, 235, 294 chaos theory 92 risks from space 14 charge-coupled devices (CCDs) 258–9 Dalton Minimum 103 rotation of 13, 26, 35, 36, 37, 39 Charles II, King 13 Daly, Reginald 186–7 spin axis 22, 35, 78 Charon 262, 317 Dampier, William 55 Tychonic model 47 Chiron 184 dark energy 12, 148, 177, 180, 259, 271, eccentricity 54 Chladni, Ernst 82, 83, 90–91, 96 eclipses 23 chondrules 91 272, 296, 298–303 lunar 20 Christian Church Dark Energy Survey 300, 302 solar 14, 116, 144 dark matter 12, 15, 164, 165, 196, 240, eclipsing binary systems 86 and geocentric model 18, 34 ecliptic 22, 52 and heliocentric model 39, 63 258, 268–71 Eddington, Arthur 14, 116, 132, 141, 144, chromatic aberration 58 D’Arrest, Heinrich 107 chromosphere 116 Darwin, Charles 231 145, 148, 152–3, 166–7, 170, 182–3 Clairaut, Alexis 77 Darwin, George 186, 187 Edgeworth, Kenneth 184, 206, 286, 312 Ehman, Jerry 210, 234

346 INDEX Einstein, Albert 150, 170, 171, 329–30 Fernie, J. Donald 76 giant molecular clouds (GMCs) cosmological constant 176, 177, Fisher, Richard 240 276–9 Fizeau, Hippolyte 103 300, 303 Flamsteed, John 13, 69, 84, 88 giant stars 138, 139, 241, 279, 302 general theory of relativity 14, 68, 73, Flandro, Gary 262, 265 Gilbert, Grove 212 Fleming, Williamina 113, 120, 124, 125, Gilbert, William 129 106, 107, 144, 148–53, 154, 167, 168, Gill, Sir David 79, 118–19, 120 169, 181, 182, 220, 259, 268, 303, 328 126, 128, 133, 141 Giotto spacecraft 207, 308 Einstein Observatory 214, 216 focal length 61 Glenn, John 245 electromagnetic radiation 190–91, 239 Foote, Albert E. 212 globular clusters 136, 137, 164–5 electromagnetic spectrum 204, 205 Ford, Kent 270 Goethe, Johann von 34 electromagnetism 111, 148 Foucault, Léon 26, 39, 103 Gold, Thomas 238–9, 300 electron degeneracy pressure 178 Fowler, Ralph 141 Goldilocks zone 294–5 electrons 282 Frankland, Edward 116 Gomes, Rodney 312–13 elements 144, 145, 162, 163, 166, 198–9 Fraunhofer, Joseph von 78, 112, 113 Goodricke, John 48, 86, 132 eLISA 328, 331 Fraunhofer lines 112, 162 Gould, Benjamin Apthorp 83 elliptical galaxies 105, 161, 241 free orbits 39 Grand Unified Theory (GUT) 272, 273 elliptical orbits 39, 50–55, 68–9, 75, 76, 92 Friedman, Herbert 215, 216 gravitational lensing 14, 153 Encke, Johann 74 Friedmann, Alexander 168, 169–70 gravitational theory 14, 43, 55, 66–73, epicycles 35, 39 equinoxes 25 G 75, 92–3, 106, 118, 148, 151, 152, precession of the 22 268, 269, 328 equivalence principle 151 Gagarin, Yuri 204, 208, 244 gravitational waves 12, 14, 73, 148, 259, Eratosthenes 18, 334 galactic “walls” 274, 275, 282, 296 268, 272, 297, 326, 328–31 Eris 184, 286, 287, 313, 314, 315, 317 galaxies Great Comet 45, 46, 69–70, 119 ESA 177, 195, 217, 227, 285, 308–11 colliding 161, 217, 221, 271 “Great Debate” 144, 161, 174–5 escape velocity 73, 181 distance of 137, 164, 240–41, 274 Greeks, ancient 18–19, 20–22, 24–5 Eudoxus 20 evolution of 240–41, 283, 285 Greenstein, Jesse 220 Euler, Leonhard 78 mapping 27 Gregorian calendar 28, 29 Europa 62, 71, 234, 264 nebulae as 89, 115, 136, 145, 158–61, 170 Grisson, Virgil “Gus” 247 European Extremely Large Telescope rotation of 15, 269–71 Grosseteste, Robert 335 (E-ELT) 290, 293, 296, 304, 326–7 see also by name Grunsfeld, John 324 European Southern Observatory (ESO) galaxy clusters 214, 274–5, 282, 296, 301 Guo Shoujing 19, 28–9 258, 259, 326–7 Galilean moons 60–63, 265 Gush, Herb 226–7 event horizon 153, 154, 155, 255 Galilei, Galileo 12, 27, 34, 39, 49, 56–63, Guth, Alan 258, 272–3, 274, 282 Ewen, Harold 210 ExoMars rover 320, 325 58, 65, 107, 129 H exoplanets 230, 259, 288–95, 305, 327 telescope 42, 44, 55, 326 extraterrestrial intelligence 12, 204, Galle, Johann 106–7 Hadley, John 43 210–11, 228–35, 238, 267, 294, Gamow, George 171, 182, 196–7, 198, Hagecius, Thaddaeus 46 295, 325 Hale, George Ellery 103, 129 extraterrestrial rovers 320–25 224, 272 Hale Telescope 129, 218, 220 Ganymede 62, 63, 71, 265 Hall, Asaph 62 F gas dwarfs 294 Halley, Edmond 22, 43, 47, 52, 64, 69–70, gas laws 167 Fabri de Peiresc, Nicolas-Claude 61 Gassendi, Pierre 64 74–7, 87, 206, 207 Fabricius, David 48–9, 86, 132 Gaultier de la Vatelle, Joseph 61 Halley’s comet 43, 70, 74–7, 207, 308 Fakhri sextant 31 Gauss, Carl Friedrich 83, 98 Harding, Karl 99 false vacuum 273 Geller, Margaret 274–5 Harriot, Thomas 61 FAST (Five-hundred-meter Aperture geocentric model 18, 20, 24, 26, 34–6, 62 Harrison, John 62 geodesic 152–3 Hartmann, William 186 Spherical Telescope) 234 geometry 18 Harvard College Observatory 100, 111, Fath, Edward 185 Gerard of Cremona 19 Fermi, Enrico 231 Ghez, Andrea 154, 218, 297 120–21, 124, 125, 128, 132–3, 162 Fermi Space Telescope 140 Giacconi, Riccardo 214–17 Harvard Spectral Classification System Fernández, Julio 184 Giant Magellan Telescope 326 113, 120, 125–6 Haumea 184, 287

INDEX 347 Hauser, Mike 282, 284 Huchra, John 274–5 K Huggins, Margaret 110, 114, 115, 116 Hawking, Stephen 148, 154, 174, 254, Huggins, William 87, 88, 104, 105, 110, Kant, Immanuel 158, 161, 250 255, 284 Kappa Andromedae b 293 114–15, 116, 158 Kapteyn, Jacobus 119, 164–5, 337 Hawking radiation 254, 255 Hulse, Russell 236 Keck Observatory (Hawaii) 292, 297, 302 Humason, Milton 175 Keenan, Philip 126 Heath, Sir Thomas 21 Huygens, Christiaan 14, 43, 58, 65, 335 Kellman, Edith 126 heliocentric model 18, 19, 21, 32–9, 55, hydrogen 113, 115, 116, 124, 125, 126, Kelvin, Lord 166 Kennedy, John F. 204, 244 62–3, 291 127, 129, 144, 162–3, 166, 167, Kepler, Johannes 48, 49, 53, 71, 96, 182–3, 196, 197, 198, 201, 226, helioseismology 213 252, 272, 282 168–9 comets 75, 76–7 helium 110, 116, 124, 125, 126, 162–3, I elliptical orbits 23, 34, 39, 42, 47, 166, 167, 182–3, 196, 197, 198, 226, Iapetus 65 52–5, 92 Ibn al-Haytham 19, 335 laws of planetary motion 44, 64, 252, 272, 282 inflation 258, 272–3 Infrared Astronomical Satellite 250 68–9 Helix planetary nebula 127 infrared telescopes 304–5 telescope 61 inside-out model 277, 278 Kepler 10b 294 Helmholz, Herman von 166 International Ultraviolet Explorer 190 Kepler 442-b 290 interplanetary scintillation (IPS) 237 Kepler Telescope/Observatory 190, 195, Henderson, Thomas 102 interplanetary space 43, 90, 267 interstellar communications 210–11 230, 292, 293 Heraclides Ponticus 20, 26, 35 Io 43, 62, 71, 265, 266 Kerr, Roy 255 ionization 140, 162, 163 Kirch, Gottfried 207 Herbig-Harp Objects 200 iron 199 Kirchhoff, Gustav 110, 112, 113, 114, 116, Islamic scholars 19, 27, 30–31 Herman, Robert 197, 224–5, 226 124, 162 J Kohlhase, Charles 263, 264, 266 Herschel, Caroline 82, 85 Korolev, Sergei 208–9 Herschel, John 82, 83, 88, 100–101, 104, James Webb Space Telescope (JWST) Koshiba, Masatoshi 252, 253 190, 195, 276, 279, 290, 293, 296, Kowal, Charles 184 105, 107 304–5, 326 Kranz, Gene 244 Herschel, William 82, 83, 84–5, 88–9, Kublai Khan 28, 29 Jansky, Karl 145, 179, 190, 218, 219, Kuiper, Gerard 184, 287, 312 96, 98, 99, 100, 103, 104, 106, 114, 297, 304 Kuiper belt 84, 184, 206, 259, 286–7, 141, 158 Janssen, Jules 116, 124 308, 311, 312, 313 Janssen, Sacharias 59 Kuiper Belt Objects 286, 287, 314, 315 Hertz, Heinrich 179 Jeans, James 337 Kumar, Shiv S 258, 339 Hertzsprung, Ejnar 86, 111, 128, 128, Jewitt, David 184, 206, 286–7 Jing Fang 23 L 135–6, 138, 139, 158 Jodrell Bank (UK) 210, 211 John of Worcester 103 Lacaille, Nicolas-Louis de 77, 79, 87 Hertzsprung–Russell diagram 124, 125, Jupiter Lagrange, Joseph-Louis 336 128, 138, 139 exploration of 262, 263, 264, 265–6, 316 Laika 208, 209 gravity 93, 291, 313, 316 Lalande, Joseph 77 Hess, Victor 111, 140 moons 34, 42, 59, 60–63, 65, 71, 148, Laniakea Supercluster 275 Hevelius, Elisabetha 335 Laplace, Pierre-Simon 82, 83, 92–3, 106, Hevelius, Johannes 75, 79, 335 234 Hewish, Antony 179, 180, 236–9 X-rays from 214, 216 107, 154, 155, 250, 251 Jutzi, Martin 186 Large Hadron Collider (LHC) 151 Hidalgo 96 Large Magellanic Cloud 27, 100–101, High-Z Supernova Search 174 133, 134, 181 Hipparchus 22, 23, 24, 30, 47, 86 Hipparcos satellite 100 Holmdel Horn 225–6 Holmes, Arthur 186 Holwarda, Johannes 132 Homestake experiment 252–3 Hooke, Robert 69 horoscopes 13, 52 Horrocks, Jeremiah 42, 64 hot Jupiters 293 Houtermans, Fritz 182, 183, 198 Howard, Edward 90 Hoyle, Fred 52, 145, 168, 171, 196, 198–9, 226, 300 Hubble, Edwin 27, 86, 102, 120, 132, 136–7, 144, 158, 161, 164, 168, 170, 174–7, 185, 193, 240, 274, 296, 300 Hubble Constant 174, 177 Hubble Space Project 174 Hubble Space Telescope (HST) 137, 177, 190, 193–5, 217, 219, 221, 258, 259, 277, 279, 300, 304, 314, 326, 327

348 INDEX Large Space Telescope (LST) 192–3 magnetic monopoles 272 Moon (cont) laser interferometry 330 phases of 13 Lassell, William 106 main sequence stars see dwarf stars seen with naked eye 58 Late Heavy Bombardment 313 moons, planetary 65, 313 Le Verrier, Urbain 68, 83, 84, 85, 106–7 Makemake 184, 287 Moore-Hall, Chester 43 Leavitt, Henrietta Swan 48, 86, 102, 111, Morbidelli, Alessandro 312–13 Malhotra, Renu 312 Morgan, William Wilson 120, 126 120, 132–7, 174 Morrison, Philip 204, 210–11, 231 Leighton, Robert 129, 213 Marconi, Guglielmo 179 Mouchez, Amédée 100 Lemaître, Georges 145, 148, 168–71, Mount Wilson Observatory (California) Mariner spacecraft 117, 204 174, 176, 196, 224, 272, 300 129, 137, 141, 174, 175 Lemonier, Pierre 84 Marius, Simon 61–2 Mueller, George 246, 247 lenses 43, 58, 59–60 Muirhead, Phil 294 Leonard, Frederick C 184 Markarian, Benjamin 185 multiverse 271 Leonov, Alexei 208 Murdin, Paul 254 Lepaute, Nicole-Reine 77 Mars Musk, Elon 321 Leuschner, Armin O 184 exploration of 262, 318–25 mythology 18 Leviathan of Parsonstown 104–5 Levison, Hal 312–13 gravity 72 N Lexell, Anders Johan 85, 106 Lick Observatory (California) 61, 63 life on 230, 234, 325 NASA light James Webb Space Telescope 279, curved 144, 152–3 moons 62, 65 pollution 12 304–5 spectrum analysis of 15, 110 retrograde motion 35, 37, 38, 53 Mars exploration 117, 234, 259, speed of 83, 148, 149–51, 272–3, 329 surface of 117, 259 wavelengths 110, 112, 329–30 320–25 LIGO (Laser Interferometer Gravitational- Maskelyne, Nevil 85 New Horizons 259, 314–17 Mather, John 282–5 observations 64, 97, 177, 190, 192, Wave Observatory) 148, 153, 259, 268, 272, 297, 304, 326, 328–31 matter 14, 148, 196, 271 194, 195, 205, 216, 227, 230, 282, Lin, Chia-Chiao 276, 277 285, 308 Lindblad, Bertil 164–5, 268, 269 Matthews, Thomas 220 Project Cyclops Report 232, 237 Lipperhey, Hans 42, 59 Maunder, Edward and Annie 129, 337 Space Race 244–9 Lizano, Susana 277 Voyager Mission 258, 262–7 Local Group 133, 275 Maury, Antonia 111, 120, 124–5, 128, navigation 13–14 Lockyer, Joseph Norman 110, 113, 116, 124 Near Earth Asteroids (NEAs) 99 longitude 62 133 nebulae 82, 83, 87, 88, 89, 101, 104–5, Lovell, James 247 145, 158, 159–60 Lowell, Percival 15, 117, 158, 159, 230 Maxwell, James Clerk 65, 110, 111, 148 spectra of 114–15, 116 Lowell Observatory 158, 160 Mayor, Michel 259, 290–95 nebular hypothesis 205, 250–51 lunar eclipses 20 Neptune Lunar Roving Vehicle 249, 320, 325 Mercury discovery of 82, 83, 84, 85, 106–7, 184 Lunokhod 1 and 2 320–21, 323, 325 exploration beyond 286–7 Luu, Jane 184, 206, 286–7 orbit 106, 107, 152, 269 exploration of 263, 264, 266–7 Luyten, Willem 178 moons 106 Lynden-Bell, Donald 297 transit of 64 orbit of 269 planetary migration 312–13 M Mesopotamia 12–13, 18 Neugebauer, Gerry 213 Messier, Charles 82, 84, 87, 88, 100, neutrinos 252–3 McClean, Frank 119 neutron stars 141, 145, 154, 178, 180–81, MACHOs (Massive Compact Halo 101, 104 205, 217, 236, 237, 238–9 Messier objects 87 neutrons 180, 181, 196–7, 236 Objects) 271 meteorites 83, 90–91, 96, 212, 313 New Horizons spacecraft 259, 262, 308, Magellanic Clouds 27, 100–101, 133, 134, 312, 314–17 meteors 190 New Technology Telescope (NTT) 258 135, 181 Metius, Jacob 59 Michell, John 70, 82, 254, 335 middle ages 26–31 Milky Way 12, 27, 58, 82, 88–9, 101, 104, 137, 221, 275, 276 shape of 164–5, 268, 269–70 size of 136 spiral nebulae 158–61 supermassive black hole 154, 297 Millikan, Robert 140 Milner, Yuri 235 mini-Neptunes 294 Mira Ceti 48–9, 86, 132 MKK system 126 Montanari, Geminiano 48 Moon composition of 244, 246, 248, 320–21 early theories about 23 eclipses 20 landings 204, 205, 209, 244–9, 320, 325 movement of 38 origin of 186–7