Sky Time Travel

The Song records say the star stayed visible at night for 642 days, until April 1056. One account says that in daylight it looked like Venus, with rays pointing in all directions and a reddish-white color. A Japanese diary and an Arabic account by the physician Ibn Butlan also mention a new star around that time. No clear European record has been found.

John Bevis spotted the cloud the star left behind in 1731. In 1758 Charles Messier, searching for the return of Halley's Comet, mistook it for a comet. That mistake pushed him to start his catalog of things that are not comets, and the Crab became its first entry, M1. Only in the 20th century did astronomers tie the nebula to the guest star of 1054.

At the Crab's heart is the collapsed core of the star: a neutron star about 20 km across that spins about 30 times a second. Radio astronomers picked up its pulses in 1968.

The Anglo-Saxon Chronicle records it as a sign in the heavens such as no one in England had seen before. Some called it the long-haired star. It first appeared on 24 April, the Chronicle says, and shone every night for a week.

In Malmesbury, according to the historian William of Malmesbury, an old monk named Eilmer looked up at it and said, "You've come, you source of tears to many mothers." Eilmer was already known for something else: as a young man he had strapped wings to his arms and jumped from the abbey tower, gliding some distance before he crashed and broke both legs.

The year bore out the fears. Harold had been crowned in January. In September a Norwegian army landed in the north, and on 14 October Harold died at Hastings. William of Normandy was crowned on Christmas Day. The tapestry that tells the story is nearly 70 meters long.

Columbus had been stuck at St. Ann's Bay since June 1503, when his last two worm-eaten ships could go no farther and he beached them. He had more than a hundred men to feed, a mutiny on his hands, and only the islanders' trade between his crew and hunger. That trade was wearing thin: the trinkets had lost their appeal, and the mutineers robbed and mistreated villages along the coast. Two of his officers had gone by canoe to Hispaniola for help.

He carried a printed astronomical almanac. Columbus later credited Abraham Zacuto's tables, though some accounts say he used Regiomontanus's. He told the local leaders that God was angry and would show it in the rising Moon. As the Moon darkened, he shut himself in his cabin, supposedly to pray, and timed the eclipse with an hourglass. Near the end of totality he came out and announced that they had been forgiven.

His son Ferdinand wrote that people came running "from every direction to the ships, laden with provisions." A rescue ship finally arrived at the end of June. Everything known about that night comes from Columbus and his son; no Taíno account of it survives, and the threat worked only because he had knowledge they did not.

By his own account, Tycho was so startled that he doubted his own eyes, and believed them only when others, shown the spot, could see the star too. It stayed visible to the naked eye into early 1574 and never moved against the stars around it.

That stillness was the point. Anything near Earth, like the Moon, shifts slightly against the background when seen from different places. Tycho found no such shift, and his figures, set beside those of the Spanish astronomer Jerónimo Muñoz, put the star far beyond the Moon. His short book De nova stella (1573) gave us the word nova. Its preface scolded those who had missed it: "O caecos coeli spectatores," O blind watchers of the sky.

In 1576 King Frederick II, eager to keep him in Denmark, gave him the island of Hven for an observatory. Today we know the star was a type Ia supernova, an exploding white dwarf, thousands of light-years away.

The star arrived on cue for the astrologers. Jupiter and Saturn had met in 1603, Mars had joined them in 1604, and astronomers across Europe, Kepler among them, were already watching that gathering. At its peak the newcomer was brighter than any star in the night sky.

Kepler measured its position and, like Tycho before him, found no shift that would put it close to Earth. He tracked its fading by comparing it with Jupiter, Venus, Mars and nearby stars, and in 1606 published De Stella Nova, "On the New Star in the Foot of the Serpent Handler." In Padua, Galileo gave three public lectures arguing that it lay far beyond the Moon. Court astronomers in Korea and China recorded it too.

What remains is an expanding shell of gas, found in 1941 at Mount Wilson Observatory, roughly 16,000 light-years away by current estimates.

Galileo first took the three points for ordinary background stars. The next night they had moved. On 13 January he saw a fourth. He drew their positions night after night, and within days he was sure they were circling Jupiter. His telescope magnified about 20 times.

He wrote it up fast. Sidereus Nuncius, "The Starry Messenger," came out in Venice in March 1610, and its first printing of 550 copies sold out quickly. Galileo named the moons the Medicean Stars, after the Grand Duke of Tuscany, Cosimo II de' Medici, and his brothers. The flattery worked: that year he became chief mathematician and philosopher to the Medici court.

The names that stuck came from a rival, Simon Marius: Io, Europa, Ganymede and Callisto. Together they are still called the Galilean moons.

It was a Sunday. Horrocks watched the Sun from sunrise, but he wrote that he was called away by "business of the highest importance" that he could not properly neglect. Historians have guessed at church duties or tutoring. When he got back to his paper at about 3:15, Venus was already on the Sun, and he had only about half an hour before sunset.

Clouds covered Salford, and Crabtree saw Venus only briefly. Horrocks wrote that his friend stood "rapt in contemplation," scarcely trusting his own senses. Horrocks used the event to correct Kepler's tables, which had forecast a near miss. He found Venus far smaller than had been thought, and from that put the Sun about 95 million kilometers away: still too close, but a large step toward the true 150 million.

He died suddenly in January 1641, about 22 years old. His account, Venus in Sole Visa, was published by Johannes Hevelius in 1662.

Halley's case rested on a pattern. In 1705 he compared the paths of two dozen recorded comets and saw that those of 1531, 1607 and 1682 matched closely. They were one object, he argued, coming back about every 76 years.

As the date neared, three French calculators, Alexis Clairaut, Joseph Lalande and Nicole-Reine Lepaute, worked through months of arithmetic by hand to find how much Jupiter and Saturn would hold the comet back. They predicted it would round the Sun around 13 April 1759, give or take a month. It came round on 13 March.

In Paris, Charles Messier was hunting for it too, but he was working from faulty predictions and did not find it until 21 January, almost a month after Palitzsch. The return was the first proof that something other than a planet orbits the Sun, and a public triumph for Newton's law of gravity.

Cook's party reached Matavai Bay in April 1769 and built an earth-walled camp they called Fort Venus. In early May the camp's brass quadrant was stolen. Cook held canoes and several leading Tahitians until it was returned. It came back "pulled to pieces" and had to be mended in time.

The day itself was perfect. Cook wrote that "not a Clowd was to be seen the whole day." Cook, Green and the naturalist Daniel Solander each timed the transit with their own telescopes, yet their times disagreed more than expected. A dark blur clung to the planet at the moments of contact, "an Atmosphere or dusky shade," in Cook's words, now called the black drop effect.

Combining results from around the world, the Oxford astronomer Thomas Hornsby put the Sun about 93.7 million miles away, within one percent of today's figure. Cook sailed on under secret orders to search for a great southern continent.

Herschel was working through the sky star by star from the garden of his house at 19 New King Street. His telescope was a reflector he had built himself, with a mirror about six inches across. Others had seen Uranus before him without knowing it. John Flamsteed logged it as early as 1690 and listed it as an ordinary star, 34 Tauri.

Herschel reported a comet. Other astronomers, Anders Lexell and Johann Bode among them, worked out its nearly circular path and saw that it had to be a planet, twice as far from the Sun as Saturn. The known solar system had doubled in size.

King George III gave Herschel 200 pounds a year on condition that he move near Windsor, so the royal family could look through his telescopes. The musician became a full-time astronomer. The house in Bath is now a museum of his work.

William was away on a visit to Germany. Caroline saw the object on the evening of August 1, found it had moved the next night, and wrote at once to Charles Blagden, secretary of the Royal Society, and to the astronomer Alexander Aubert. She began modestly, venturing "to trouble you in his absence." Her letter was read to the Royal Society that November and printed in its journal.

The novelist Fanny Burney called it "the first lady's comet," and Joseph Banks called Caroline "the lady's comet hunter." The next year King George III granted her £50 a year as William's assistant, the first money she had ever earned in her own right. In 1835 she and Mary Somerville became the first women elected honorary members of the Royal Astronomical Society.

Piazzi was not hunting for planets. He was looking for a star listed in a catalogue by the French astronomer Lacaille and found a faint object that would not stay put. He followed it until illness stopped him in February. He announced it as a comet, but privately told the Milan astronomer Barnaba Oriani it might be "something better than a comet."

Then it slipped into the Sun's glare and was lost. Carl Friedrich Gauss, then 24, worked out a new way to compute an orbit from Piazzi's few weeks of positions, and near the end of 1801 Franz Xaver von Zach and Heinrich Olbers found it again where Gauss said it would be.

Piazzi named it Ceres, for the Roman goddess of agriculture and patron of Sicily. It is about 940 kilometers across and holds between a quarter and 40 percent of the asteroid belt's mass, depending on the estimate. NASA's Dawn spacecraft began orbiting it in 2015 and traced its bright spots to salty brine.

Reports came in from across eastern North America and beyond, from Canada to Jamaica. One later estimate put the total at more than 240,000 meteors in about nine hours. Europe, where it was already daytime, saw nothing.

At Yale, the mathematician Denison Olmsted collected eyewitness accounts and noticed that the trails, traced backward, all met at one spot in the constellation Leo. He argued that Earth had run into a cloud of particles in space. It was the start of meteor science. Decades later, astronomers tied the Leonids to a comet, Tempel-Tuttle, whose dust Earth crosses every November.

The Lakota kept winter counts, picture calendars that name each year for its most memorable event. All 14 of the counts held at the Smithsonian mark 1833 as the year the stars fell, and historians have used it to line the counts up with the Western calendar.

The letter reached Galle on the morning of 23 September. The observatory's director, Johann Franz Encke, let him use the big Fraunhofer refractor that night. It happened to be Encke's 55th birthday. Heinrich d'Arrest, a student, overheard and asked to come along.

Le Verrier had told them to look for a small disk, and at first nothing stood out. Then d'Arrest remembered a new chart of that patch of sky, Carl Bremiker's Hora XXI, so new that only Berlin had it yet. Galle called out stars at the eyepiece while d'Arrest checked them against the chart, until d'Arrest came to one that was not on it. On the following nights it moved against the stars, as a planet should.

Galileo had drawn Neptune in 1612 and 1613 but took it for a star. In England, John Couch Adams had made similar calculations, and a long quarrel over credit followed. Galle's telescope survives in the Deutsches Museum in Munich.

The idea came from August Busch, director of the Royal Observatory at Königsberg, who hired a local professional with no background in astronomy. Records spell the daguerreotypist's name several ways. He is usually given as Johann Julius Friedrich Berkowski.

He used a small 6 cm telescope fixed to the observatory's 15.8 cm Fraunhofer heliometer. The Sun's image on the plate was less than 8 mm across, yet it shows the corona and at least five prominences, the glowing flames at the Sun's edge. A second try, 45 seconds long, failed when light flooded the plate.

The original plate has since been lost, but copies survive, one of them at the observatory in Jena. Nine years later, Warren De la Rue's photographs of the 1860 eclipse in Spain helped settle that the prominences belong to the Sun, not the Moon.

The storm had a visible start. Just before noon the day before, the English astronomer Richard Carrington was sketching sunspots when two patches of intense white light flared among them and faded within about five minutes. Another Englishman, Richard Hodgson, saw the same thing on his own. It was the first solar flare anyone had recorded.

The burst of solar material that followed reached Earth in about 17.6 hours, a trip that usually takes several days. Aurora was reported as far south as Colombia, close to the equator, and newspapers filled columns with readers' accounts.

The world had little electrical equipment to break in 1859. A 2013 study for Lloyd's of London estimated that a storm like it today could cost the United States between 600 billion and 2.6 trillion dollars, mostly through damage to the power grid.

Janssen did not stop when the eclipse ended. Clouds covered the Sun after totality, but the next morning he set up again, tuned his instrument to the yellow line, and found the same glow at the Sun's edge in full daylight. It meant the prominences could be studied on any clear day.

His report took about two months to reach Paris. In England, Norman Lockyer had worked out the same daylight method on his own and saw the line on 20 October. Their letters arrived at the French Academy on the same day, 26 October 1868, and the Academy later struck a medal with both men's profiles. Lockyer named the line D3, since it sat beside sodium's two D lines, and argued that it came from an unknown element. Many scientists doubted him.

The proof came in 1895, when William Ramsay found the same yellow line in gas freed from a uranium mineral called cleveite.

The nearest settlement of any size was the trading post at Vanavara, about 65 km away. A farmer there, Semyon Semyonov, later wrote that he was thrown about six meters off his porch and lost consciousness for a moment. Evenki herders closer in lost tents and reindeer, and accounts gathered later name at least three Evenki people who died.

No scientist reached the site for 19 years. In 1927 the mineralogist Leonid Kulik led the first scientific expedition to reach it, expecting a giant crater and perhaps a buried iron meteorite. There was no crater. At the center, trees still stood upright, stripped of their branches, while for miles around they lay flat, pointing away from the middle.

That pattern is the main clue. Most researchers think a stony object perhaps 50 or 60 meters across exploded in the air 5 to 10 km up, with the force of several megatons of TNT.

The scare had a scientific start. In February 1910, astronomers at Yerkes Observatory reported cyanogen, a poisonous gas, in the comet's tail. The New York Times reported the French astronomer Camille Flammarion musing that it might "impregnate the atmosphere and possibly snuff out all life on the planet." Most astronomers said the tail was far too thin to do any harm, but the idea had already spread.

The comet made other news that spring. Mark Twain, born just after its 1835 visit, had written that he expected to go out with it. He died on 21 April 1910, the day after it rounded the Sun.

When the tail swept past, nobody could detect anything at all in the air. The anti-comet pills, which one account says were sugar and quinine, did no harm either.

It was a double expedition. While Eddington and Edwin Cottingham went to Príncipe, Andrew Crommelin and Charles Davidson of the Greenwich observatory set up at Sobral in northern Brazil, in case one site was clouded out. On Príncipe a storm with heavy rain lasted until about noon. Afterward he cabled home that it had been cloudy but he was "hopeful."

Einstein's theory said starlight grazing the Sun should bend by about 1.75 arcseconds, twice what Newton's physics allowed. The clearest plates came from a small telescope at Sobral, and they came out close to Einstein's figure.

The results were announced at a joint meeting of the Royal Society and the Royal Astronomical Society on 6 November 1919. The next day the Times of London ran the headline "Revolution in Science." Critics later asked whether Eddington had picked the data that suited him, but a 1979 remeasurement of the Sobral plates backed him up.

Percival Lowell, who founded the observatory, had hunted for a "Planet X" beyond Neptune for a decade before he died in 1916. Tombaugh was hired to take up the search. He photographed the same strips of sky days apart and compared the plates in a blink comparator, a machine that flicks quickly between two images so anything that has moved seems to jump. Pluto's dot was on plates taken on 23 and 29 January. He went to the director and said, "Doctor Slipher, I have found your Planet X."

The observatory took more photographs to be sure and announced the find on 13 March. Venetia's grandfather read about it in the Times the next morning. The name was adopted on 1 May, helped by the fact that its first two letters are Percival Lowell's initials.

In 2015 the New Horizons spacecraft flew past Pluto carrying a dust counter named for Venetia Burney and an ounce of Tombaugh's ashes.

The man who made the weather call was a Scottish meteorologist, Group Captain James Stagg, Eisenhower's chief weather adviser. The invasion was first set for 5 June. With a storm coming in from the Atlantic, Stagg urged a delay, and early on 4 June Eisenhower postponed by a day. Stagg's team then spotted a short lull for the morning of 6 June, and Eisenhower gave the order to go.

The Germans saw the same bad weather and relaxed. Field Marshal Erwin Rommel, in charge of the coastal defenses, had gone home to Germany for his wife's birthday, which fell on 6 June.

Waiting would have been worse. The next run of suitable tides came about two weeks later. On 19 June the worst storm to hit the Normandy coast in 40 years blew up and wrecked one of the two artificial harbors the Allies had towed across the Channel.

Sputnik was 58 cm across and weighed 83.6 kg, with four long antennas swept back behind it. It went around the Earth every 96 minutes. Its radio ran on batteries, which gave out after 22 days. The silent ball stayed in orbit until January 1958, when it fell back and burned up.

The man behind it was Sergei Korolev, whose name the Soviet government kept secret. His team had built the R-7 as a missile to carry a nuclear warhead. The satellite itself was a quick, simple design, put together when a much bigger science satellite fell behind schedule. That one flew later as Sputnik 3.

Pravda first gave the launch only a few paragraphs. The shock came from abroad. Within a year the United States had created NASA and passed a law putting money into students studying math and science.

Vostok 1 flew itself. Doctors did not know how a person would cope with weightlessness, so the manual controls were locked, with the unlock code sealed in an envelope on board. Several people told Gagarin the code before launch anyway. His orbit took him as high as 327 km.

Near the end, Gagarin ejected at about 7 km and came down by parachute, apart from his capsule. The Soviet Union kept that quiet until 1971, because the rules for an official flight record then said the pilot had to land with his craft. He came down southwest of the city of Engels, near the Volga. He told the woman and girl who met him not to be afraid: he was a Soviet citizen like them, come down from space, and he needed a telephone to call Moscow.

He never flew in space again. Gagarin died in a jet crash on a training flight in 1968, at 34.

The lord mayor is said to have called the idea a waste of public money, but the state premier, David Brand, backed it, and Perth's street lights were left on until dawn. Rockingham, down the coast, joined in.

Glenn passed over Western Australia around midnight local time. The flight transcript records him telling the tracking station, "The lights show up very well and thank everybody for turning them on." Later in the flight he reported that cloud hid the lights at Woomera, but that Perth's had been very clear.

Perth did it again in 1998, when Glenn, then 77, flew on the space shuttle Discovery. He said the lights looked even more vivid than they had 36 years before.

Vostok 6 flew alongside Vostok 5, whose pilot, Valery Bykovsky, had gone up two days earlier. The two craft were in radio contact within hours, and Tereshkova also spoke by radio with Nikita Khrushchev. She was 26, one of five women chosen in February 1962 from more than 400 applicants.

She had no pilot training. Parachuting was one of the requirements, and with reason: Vostok pilots did not ride their capsules to the ground. On 19 June she ejected during the descent and came down under her own parachute in the Altai region, bruising her nose in the gusty wind.

Hers was the last flight of the Vostok program. No other woman flew in space for 19 years, until Svetlana Savitskaya in 1982, and Tereshkova is still the only woman to have flown a space mission alone.

The peak came around 11:54 UT, just before 5 in the morning in Arizona. At Kitt Peak, a team led by Dennis Milon watched the count climb from about 30 a minute to some 40 a second, a pace that held for roughly 20 minutes before it fell away. Witnesses said the sky seemed to rain shooting stars.

At Table Mountain, the Jet Propulsion Laboratory's observatory at 7,500 feet near Wrightwood, James Young photographed more than a thousand meteors in 90 minutes, among them 22 bright fireballs.

The Leonids are dust shed by Comet Tempel-Tuttle, and their storms tend to come about every 33 years. Astronomers had promised one in 1899 that never came, and the public scorned them for years. The often quoted 1966 peak, close to 150,000 meteors an hour, is still debated.

Nobody had planned a picture of the Earth rising. On their fourth pass around the Moon, Bill Anders saw it coming up over the gray horizon and reached for a camera. He took one frame in black and white, then called for color film. The color frame became one of the best-known photographs ever made.

In the Christmas Eve broadcast, Anders, Jim Lovell and Frank Borman took turns reading the first ten verses of Genesis. Borman closed with "good night, good luck, a Merry Christmas and God bless all of you, all of you on the good Earth." By one estimate, about a quarter of the people alive saw it, live or later.

1968 had been a hard year of war, assassinations and riots. Afterward a stranger sent Borman a telegram: "Thank you Apollo 8. You saved 1968."

Liftoff came at 9:32 in the morning. The Saturn V stood 363 feet tall, and its five first-stage engines together made about 7.5 million pounds of thrust. Former President Lyndon Johnson and Vice President Spiro Agnew watched from the guest stands. Twelve minutes later the crew was in orbit.

The day before, the civil rights leader Ralph Abernathy had led a march of poor families, with mule-drawn wagons, to the space center. He argued that the nation's money should go to feeding the hungry. NASA's administrator, Thomas Paine, walked out to meet them. He said that if not launching would solve the problem of poverty, NASA would not push the button. Then he offered the group places to watch the launch, and Abernathy prayed for the astronauts' safety.

The hardest part came hours earlier. As Eagle went down that afternoon, its computer kept raising alarms, codes 1201 and 1202, meaning it had more work than it could finish. Controllers judged it safe to keep going. Then Armstrong saw that the autopilot was heading for a field of boulders, took over part of the flying and went looking for level ground. Eagle touched down at 3:17 PM Houston time. Mission control thought about 25 seconds of fuel margin were left. Later analysis put it closer to 50.

Buzz Aldrin followed Armstrong down the ladder about 19 minutes after him. They spent about two and a half hours outside and brought back 47.5 pounds of rock and soil.

Michael Collins circled overhead alone in Columbia, out of radio contact every time he passed behind the Moon.

The aircraft was Concorde 001, the first prototype, flown by the French test pilot André Turcat. The astronomer Pierre Léna had put the idea to him over lunch at Toulouse a year before. Four portholes were cut into the roof so instruments could look straight up at the Sun.

Seven astronomers from France, Britain and the United States flew aboard. The plane took off from Las Palmas in the Canary Islands, met the Moon's shadow over West Africa at about 55,000 feet, ran with it across the Sahara, and landed in Chad. Mauritania closed its airspace to other traffic so the flight could go ahead.

The science was modest. Léna said later that the five experiments all succeeded, "but none of them revolutionized our understanding of the corona." The plane, roof portholes and all, is now at the Air and Space Museum at Le Bourget, outside Paris.

Ehman, a volunteer on the project, found it a few days later while going through the printouts by hand. The characters he circled, 6EQUJ5, are not a message. Each one is the signal's strength over ten seconds, and the "U" marks a peak about 30 times the usual spread of background noise. It sat near 1420 MHz, the natural radio note of hydrogen, a frequency scientists had suggested since 1959 that another civilization might choose.

Big Ear could not steer. Its flat metal reflector, about 340 feet long, waited while Earth's turning swept the sky past. It had two feed horns, so a steady source should have shown up twice, a few minutes apart. It appeared only once.

Searches of that patch of Sagittarius since, including with the Very Large Array in the 1990s, have found nothing. Big Ear was taken down in 1998, and the land went to a golf course.

Much of the Northwest woke to clouds. Portland, the biggest city in the path, stayed under thick overcast. At Goldendale Observatory an estimated 10,000 people waited, and the sky opened in time for totality. Air traffic controllers guided more than 1,000 aircraft around the path that morning. Totality lasted up to 2 minutes 49 seconds as the shadow ran on across Montana and into Canada, where Winnipeg had clear skies.

The writer Annie Dillard watched from a hillside in the Yakima Valley and later turned the morning into her essay "Total Eclipse." Other watchers screamed as the shadow came, and it shook her. "Seeing a partial eclipse bears the same relation to seeing a total eclipse as kissing a man does to marrying him," she wrote.

The flight had already slipped two days. On April 10 a timing mismatch between Columbia's computers stopped the countdown. Young was a veteran of two Moon flights, making his fifth trip to space; Crippen was a rookie. At liftoff Crippen's heart rate climbed to almost 130, while Young's stayed near 90.

Columbia flew for 2 days, 6 hours and 20 minutes. In orbit the crew could see damaged tiles on the pods near the tail, and afterward NASA counted 16 lost and 148 damaged. The pressure wave from the boosters at ignition had also bent a strut and pushed the body flap past its expected limit, something the crew learned only later.

From the Florida shore, people saw a craft unlike any before, its big fuel tank painted white, as it was only on this flight and the next. After landing, Young summed it up: "This is the world's greatest all electric flying machine."

Shelton, a 29-year-old Canadian, was the resident astronomer at the University of Toronto's station on the mountain. His plate was a three-hour exposure from an old 10-inch telescope, and the new star had brightened by at least eight magnitudes since the night before. That same night the telescope operator Oscar Duhalde had noticed it with his own eyes, and in New Zealand the amateur Albert Jones spotted it within a day. All three share the credit.

The star had already announced itself. Two to three hours before its light arrived, detectors in Japan, the United States and the Soviet Union caught a burst of 25 neutrinos, the first ever recorded from a supernova. The light had left about 168,000 years earlier.

The star that died, cataloged as Sanduleak -69 202, was a blue supergiant, which surprised astronomers. The supernova kept brightening until May, reaching about third magnitude.

Carolyn Shoemaker spotted it in March 1993 on images from Palomar's 18-inch Schmidt telescope, taken with her husband Gene and David Levy. She said it looked like a "squashed" comet. Its orbit showed it had passed about 25,000 miles above Jupiter's clouds in July 1992, close enough for the planet's pull to tear it into more than 20 pieces.

They struck at about 37 miles per second, just around the edge of Jupiter out of view from Earth. The Galileo spacecraft, still on its way, had a direct view, and within minutes the planet's spin carried each site into sight. The largest piece, fragment G, hit on July 18 with an energy estimated at 6 million megatons of TNT and left a dark spot more than 7,000 miles across.

It was the first collision between two solar system bodies that anyone had watched as it happened. It also gave new urgency to the search for objects that could one day hit Earth.

Hale had spent many hundreds of hours searching for comets without finding one. Just after midnight on July 23, 1995, he saw a fuzzy spot near the star cluster M70 in Sagittarius. The same night Thomas Bopp, who did not own a telescope, saw it through a friend's at a ranch south of Phoenix. The comet was then more than seven times Earth's distance from the Sun, far out for a comet to be found, a hint of its unusually large icy core, roughly 37 miles across.

Even at its closest it stayed about 120 million miles away. By April 9, 1997, a survey found that 69 percent of Americans had seen it. Hale-Bopp will not be back for more than two thousand years.

The forecast came from a new way of thinking about the shower. Instead of treating the dust of Comet Tempel-Tuttle as one broad cloud, astronomers David Asher and Robert McNaught traced the separate trails it leaves on each pass around the Sun. Their model had timed the 1999 storm within minutes. For 2001 it pointed to a trail shed in 1767, crossing Earth's path over the Americas.

The American peak came near 10:30 UT, about 2:30 in the morning in California, at more than 1,000 meteors an hour. Hours later a second storm, from older trails, fell over East Asia and Australia. Leonids hit the air at about 44 miles per second, the fastest of the major showers, and the brightest can leave glowing trains behind. Rates stayed at storm level longer than in 1999.

The first person known to have watched one was Jeremiah Horrocks, a young Englishman who saw Venus on the Sun from his home near Preston in December 1639, half an hour before sunset. In London in 2004 the whole crossing fit into a June morning, starting soon after 6 a.m. and ending around 12:30 in the afternoon.

The 1700s expeditions included James Cook's voyage to Tahiti in 1769. Their timings were blurred by the "black drop," a smear that makes Venus seem to cling to the Sun's edge as it enters or leaves. Even so, the results put the Sun about 95 million miles away, close to the true 93 million.

In 2004 the European Southern Observatory ran the experiment again with the public. About 1,500 observers sent in 4,550 timings, and their combined answer came within about 7,000 miles of the modern value.

Robert McNaught found the comet in August 2006 on images from the Uppsala Southern Schmidt telescope at Siding Spring, Australia, during a routine search for near-Earth asteroids. It passed the Sun on 12 January 2007, about 25 million km out, and for a few days it could be seen in daylight a few degrees from the Sun. At its brightest it reached about magnitude -5.5, brighter than Venus.

ESO called it the brightest comet in more than 40 years, outshining Hale-Bopp and West. At its longest the dust tail stretched some 35 degrees, combed into bands called striae. At Paranal the tail still rose above the horizon after the head had set, a fan of light that ESO said was reminiscent of an aurora.

In February the Ulysses spacecraft flew through the comet's ion tail. The comet came straight from the Oort cloud and is heading back out.

Terry Lovejoy, an amateur astronomer in Queensland, Australia, found the comet on 27 November 2011 with a 20 cm telescope and a camera. It was a Kreutz sungrazer, one of a family of comets that swing extremely close to the Sun, and the first of them found from the ground in 40 years.

On 16 December it passed about 140,000 km above the Sun's surface. Most researchers expected it to be destroyed. Instead NASA's Solar Dynamics Observatory watched it come out from behind the Sun. It seemed to lose its tail in the corona and grow it back.

The reprieve was short. Within days the nucleus broke apart, and by about 20 December its bright core was gone. The tail seen over Santiago was dust left by a comet that no longer had a solid heart. Astronaut Dan Burbank photographed it from the International Space Station that same week.

At nearly a ton, Curiosity was too heavy to bounce down on airbags as earlier rovers had. So a rocket-powered descent stage hovered over the ground, lowered the rover on nylon ropes, cut them once its wheels were down, and flew off to crash a safe distance away. It had never been tried on another planet. Overhead, NASA's Mars Reconnaissance Orbiter photographed the rover drifting down under its parachute.

It landed inside Gale Crater, about 1.5 miles from the center of its target after a trip of some 350 million miles. Its first picture came from a hazard camera, through the camera's clear dust cover, which was still on. Built for a two-year mission, Curiosity is still working, climbing the layered slopes of Mount Sharp, a mountain 3.4 miles high in the middle of the crater.

Nobody saw it coming. The rock approached from within about 15 degrees of the Sun, a part of the sky asteroid telescopes cannot search, and entered the atmosphere over the Kazakhstan-Russia border at about 19 km per second. Its burst released close to 500 kilotons of TNT, about 30 times the Hiroshima bomb, and infrasound stations around the world picked it up.

More than 7,200 buildings were damaged. At School No. 37, teacher Yulia Karbysheva saw the flash and ordered her 44 fourth graders under their desks before the shock wave hit. She was badly cut by glass. The children were unhurt.

Pieces fell as meteorites. One punched a hole about 6 m wide in the ice of Lake Chebarkul, and a 654 kg piece was raised from the lake bed that October. By coincidence another asteroid, 2012 DA14, passed Earth about 16 hours later. The two were unrelated.

The shadow reached the Oregon coast at about 10:16 in the morning Pacific time and left South Carolina at about 2:44 in the afternoon Eastern, crossing 14 states in about an hour and a half. The very longest totality, 2 minutes 41.6 seconds, fell just south of Carbondale, near Giant City State Park.

About 14,000 people filled Southern Illinois University's stadium. Clouds drifted in minutes before totality, and the crowd cheered them away; a few clear seconds were enough.

A University of Michigan survey done with NASA later found that 88 percent of American adults had watched in some way, in person or on a screen, and about 20 million traveled to see it.

Falcon Heavy was three Falcon 9 first stages joined side by side, with 27 engines firing at liftoff. High winds held the launch for more than two hours. The two side boosters were used ones: both had already flown in 2016, one for the Thaicom 8 satellite and one for a space station cargo run.

The center core did not make it home. Only one of the three engines meant to slow it lit, and it hit the Atlantic at about 300 miles per hour, roughly 100 meters from the drone ship waiting for it.

The car carried a few jokes for anyone who finds it. The words "Don't Panic" are on the dashboard screen, and a circuit board reads "Made on Earth by humans." It ended up in an orbit around the Sun that swings out beyond the orbit of Mars.

Bill Ingalls made the picture on 18 July 2020 with a 10-second exposure, long enough to stretch the station's light into a line. Five people were aboard: NASA astronauts Chris Cassidy, Doug Hurley and Bob Behnken, and cosmonauts Anatoly Ivanishin and Ivan Vagner.

The comet was named for NEOWISE, the NASA space telescope that found it on 27 March 2020. It passed the Sun on 3 July, closer than Mercury ever comes, and was nearest Earth on 23 July, about 103 million km away. Its nucleus is about 5 km across. It showed a golden dust tail and a blue gas tail, and it was the brightest comet in northern skies since Hale-Bopp in 1997. It will not be back for about 6,800 years.

Nothing was actually close. The two planets were hundreds of millions of miles apart, and only lined up from where we stand as Jupiter, on its faster inside track, overtook Saturn. At their nearest they were a tenth of a degree apart in the sky. A pinkie finger held at arm's length could cover both.

Jupiter and Saturn pass each other about every 20 years, but most passes are much wider. The 1623 meeting, thirteen years after Galileo first turned a telescope on both planets, sat so near the Sun that it was hard to see. For one this close and this easy to watch, you have to go back to 1226. The next comparable pairing comes in March 2080, low in the morning sky.

The flight almost did not go that night. While the rocket was being fueled, a hydrogen valve in the base of the launch tower began to leak. NASA sent a three-man "red crew" out to the pad, beside a mostly fueled moon rocket, to tighten the fittings. The leak stopped and the countdown went on. The launch had already been scrubbed twice in late summer and delayed by two hurricanes, Ian and Nicole.

SLS made about 8.8 million pounds of thrust at liftoff. Orion spent about 25 and a half days in space, passed within 80 miles of the Moon's surface, and on November 28 reached 268,563 miles from Earth, the farthest a spacecraft built for people had ever gone. Its riders were a mannequin named Commander Moonikin Campos and a plush Snoopy. It splashed down off Baja California on December 11.

About 44 million people lived in the path of totality, 32 million of them in the United States. Dallas was the largest U.S. city in it, and totality there began a little after 1:40 in the afternoon. The longest totality anywhere, 4 minutes 28 seconds, fell near the town of Nazas in Mexico.

The pink flames were prominences, great loops of glowing gas at the Sun's edge, many times larger than Earth. In Dallas, Venus and Jupiter shone brightly during totality. NASA also flew two high-altitude WB-57 jets along the path and launched sounding rockets from Virginia to study how the upper air reacted. The next total eclipse visible from the lower 48 states comes in 2044.

The storm came from a sunspot region, number 3664, about 17 times the size of Earth. Over several days it threw a string of clouds of solar gas, called coronal mass ejections, toward us. The first arrived on May 10, and the storm reached G5, the top of NOAA's scale, for the first time since the Halloween storms of October 2003.

The lights were reported from the Florida Keys, the Bahamas, Jamaica, Puerto Rico and Mexico's Yucatán, and in the Southern Hemisphere as far north as Queensland in Australia. In the Midwest, some GPS-guided tractors drifted off course in the middle of planting season. The event is now often called the Gannon storm, after the space weather physicist Jennifer Gannon, who died suddenly days before it arrived.