The sky keeps revising what we think we know. These stories run from ancient Greece to today's space telescopes, with overlooked astronomers, figures that changed when better measurements arrived, and a few popular beliefs about the heavens that turn out to be wrong. Along the way are a comet that came back on schedule, stars that were not what they seemed and worlds that changed names and categories.
Every tile in a Space and Astronomy game carries one of these. Open one to read it now, or leave them for the board to hand you.
Solar System
nine stories
1Closest to the Sun, but not the hottest
On the tile: MercuryMyth busted
It seems logical that the planet closest to the Sun would be the hottest, but that title belongs to Venus, whose dense atmosphere traps heat. Mercury lives at extremes instead. Daytime surface temperatures can reach 800 degrees Fahrenheit, and nights can drop to minus 290. Its days are long, too: one full cycle of day and night lasts 176 Earth days, just over two Mercury years. And deep inside craters near its poles, in regions of permanent shadow, Mercury may even hold water ice.
On Venus, tomorrow is a long way off. The planet turns so slowly that one full spin takes 243 Earth days, longer even than its year, a single trip around the Sun that takes only 225 Earth days. Venus also spins backward compared with Earth, so the Sun would rise in the west and set in the east. Measured from one noon to the next, a full day on Venus lasts about 117 Earth days. The surface would be no place to wait for sunset. It is about 872 degrees Fahrenheit, hot enough to melt lead.
Many people believe Earth is closer to the Sun in summer, and that this is why summer is hot. For the Northern Hemisphere it is the other way around. Earth's orbit is not a perfect circle. Its closest point to the Sun, about 91.4 million miles, comes in January, and its farthest, about 94.5 million miles, comes in July. That gap of over 3 million miles does not make much difference to our weather. The seasons come from Earth's axis, which is tilted 23.4 degrees.
The half of the Moon we never see from Earth is sometimes called the dark side, but NASA calls that name misleading. The Moon rotates at the same rate that it circles Earth, so the same hemisphere always faces us, yet different parts of the Moon take turns in sunlight and darkness. During a new moon, when the side facing us is having its night, the far side is in full sunlight. No human saw the far side at all until 1959, when a Soviet spacecraft flew past.
Mars has blue sunsets. On April 15, 2015, the 956th Martian day of its mission, NASA's Curiosity rover watched the Sun set from Gale Crater. It was Curiosity's first sunset observed in color, recorded with a camera that sees color much as human eyes do. The images show blue light gathered close to the setting Sun. The cause is dust: its fine particles let blue light pass through the Martian atmosphere more efficiently than longer-wavelength colors, and the effect is strongest near sunset, when sunlight crosses the longest path of air.
Pluto was not the first world to lose its planet status. Giuseppe Piazzi spotted Ceres from Palermo on January 1, 1801, and it was listed as a planet in astronomy books for over half a century. As more objects turned up in the same region between Mars and Jupiter, it was reclassified as an asteroid, and in 2006 it became a dwarf planet. In 2015 NASA's Dawn made it the first dwarf planet visited by a spacecraft. Its name, for the Roman goddess of harvests, also gave us the word cereal.
Saturn's rings are vast in one direction and startlingly thin in the other. The ring system extends up to 175,000 miles from the planet, yet in the main rings its vertical height is typically about 30 feet. The rings are thought to be pieces of comets, asteroids or shattered moons torn apart by Saturn's powerful gravity, and each ring orbits at a different speed. The planet itself is the only one in our solar system with an average density less than water. It could float in a bathtub, if a bathtub that large existed.
Neptune was the first planet located through mathematical prediction rather than regular observation of the sky. The French mathematician Urbain Le Verrier calculated the position of an unseen planet that could explain changes in the orbit of Uranus. He sent his prediction to Johann Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Galileo had seen it long before, recording it as a fixed star in 1612 and 1613. One Neptune year lasts about 165 Earth years, so it finished its first orbit since discovery only in 2011.
On March 14, 1930, at breakfast in Oxford, England, Falconer Madan read out the news of a newly discovered planet and wondered what it would be called. His 11-year-old granddaughter, Venetia Burney, suggested Pluto, the Roman god of the underworld. Madan passed the idea to astronomer Herbert Hall Turner, who cabled Lowell Observatory. The name came with a bonus: its first two letters were the initials of Percival Lowell. It was announced on May 1, 1930. The knack ran in the family. Her great-uncle Henry Madan had suggested the names Phobos and Deimos for the moons of Mars.
Sunlight takes about eight minutes to reach Earth, but its energy set out long before that. It is released in the Sun's core, where the temperature is about 27 million degrees Fahrenheit and nuclear reactions fuse hydrogen into helium. From there the radiation bounces around the Sun's radiative zone, taking about 170,000 years to reach the top of the convection zone. The Sun formed about 4.6 billion years ago, and scientists predict it will last another 5 billion years or so before it becomes a white dwarf.
In late 2019 Betelgeuse, the bright orange star in the constellation Orion, grew visibly darker, a change noticeable even to the naked eye. Some online speculation suggested the star might be about to die in a supernova. By April 2020 it had returned to its normal brightness, and astronomers using ESO's Very Large Telescope worked out what had happened. Some time before, the star had ejected a large bubble of gas. When a patch of its surface then cooled, the gas condensed into dust, and that dusty veil shaded the star.
Sirius, the Dog Star, is the brightest star in the night sky, and it hides a faint companion. In 1844 the German astronomer Friedrich Bessel deduced from changes in the motion of Sirius that something unseen was pulling on it. In 1862 the American telescope maker Alvan Graham Clark finally spotted it while testing one of the best telescopes in the world at the time. Sirius B is a white dwarf with about the mass of the Sun packed into a ball slightly smaller than Earth, and its surface gravity is hundreds of thousands of times Earth's.
In 1054, Chinese astronomers took note of a guest star, a new light that for nearly a month could be seen in the daytime sky. It was a supernova explosion about 6,500 light-years away, and its remains are now the Crab Nebula. At the center spins a neutron star, the ultra-dense core of the star that exploded. Like a lighthouse, it sends out twin beams of radiation, which make it appear to pulse 30 times per second as it rotates.
In February 1987 astronomers saw a supernova in the Large Magellanic Cloud, 160,000 light-years away, so the explosion itself had happened about 160,000 years earlier. It was the first supernova visible to the naked eye since Kepler's Supernova in 1604. About two hours before its light was seen, three observatories recorded a burst of neutrinos lasting only a few seconds. Astronomers long sought whatever the explosion left behind. In 2024 a James Webb Space Telescope team reported direct evidence of it: high-energy emission from what is most likely a young neutron star.
Edmond Halley discovered the star cluster M13 in 1714. More than 100,000 stars swarm inside it, 25,000 light-years away. On November 16, 1974, at the dedication of an upgrade to the Arecibo radio telescope in Puerto Rico, astronomers beamed a message toward it: 1,679 binary bits representing the chemicals of life, the formula for DNA, a crude diagram of our solar system and simple pictures of a human being and the telescope. Sending it took about three minutes. Donald Campbell, then a research associate at Arecibo, later called it strictly a symbolic event.
Volunteers searching NASA's Kepler data for planets flagged one star's light as bizarre and interesting. Kepler had seen it dim by up to 20 percent over a matter of days. A 2016 study formally introduced the star, nicknamed Tabby's Star for lead author Tabetha Boyajian, and its strange dips fueled talk of an alien megastructure. Then a 2017 study using NASA's Spitzer and Swift missions found the star dimmed less in infrared than in ultraviolet light, pointing to an uneven cloud of fine dust and all but ruling out the megastructure.
For years astronomers expected the Milky Way to collide with the Andromeda Galaxy. In 2012, Hubble measurements led to a prediction of a direct impact in no more than 5 billion years. In 2025 a team led by Till Sawala of the University of Helsinki revisited the question with newer data from Hubble and ESA's Gaia space telescope, running 100,000 simulations. They found about a 50-50 chance of a collision within the next 10 billion years, and only around a 2 percent chance of a head-on crash in 4 to 5 billion years.
For 30 years, teams led by Reinhard Genzel and Andrea Ghez measured the orbits of stars very close to the center of the Milky Way. The stars were circling something invisible, compact and very massive, and the work shared the 2020 Nobel Prize in Physics. On May 12, 2022, the Event Horizon Telescope collaboration released the first image of that object: a dark shadow inside a bright ring of light bent by gravity. It is a black hole about four million times as massive as the Sun, some 27,000 light-years away.
In the third century BC, Aristarchus of Samos proposed that Earth revolves around the Sun. His writing on that idea has been lost. We know of it mainly because Archimedes summarized it in The Sand-Reckoner, describing a Sun that stays unmoved while Earth circles it. Aristarchus's only surviving work uses geometry to size up the sky. He estimated that the Sun was about 20 times as far away as the Moon and 20 times its size. Both figures were far too small, but the fault lay in his instruments, not his reasoning.
In 1566, while at the university in Rostock, Tycho Brahe quarreled with another Danish student, and in the duel that followed he lost part of his nose. The artificial nose he wore afterward has long been described as silver, or silver and gold. When his remains were exhumed in Prague in 2010, researchers took a small bone sample from the nose. Its green stain held traces of copper and zinc, a sign that the nose was brass. The same team ruled out mercury poisoning as the cause of his death in 1601. A 2018 study concluded that the exact cause cannot be established.
3The comet hunter famous for things that were not comets
On the tile: Messierc. 1758
Charles Messier hunted comets so avidly that King Louis XV nicknamed him the Ferret of Comets. He discovered 13 and co-discovered seven more. Yet he is remembered for things that were not comets. While sweeping the sky for the return of Halley's Comet, he found a small patch of light in Taurus that showed no movement. He later made it M1, the first entry in a catalog meant to save comet hunters from wasting time on objects that only looked like comets. The catalog now lists 110 objects.
As a girl in Hanover, Caroline Herschel essentially lived the life of a servant. In 1772 she joined her brother William in Bath, England, and sang in oratorios such as Messiah, sometimes five nights a week. She became William's astronomy assistant and then made discoveries of her own, finding eight comets between 1786 and 1797. In 1787 King George III gave her a salary of 50 pounds a year. The Royal Astronomical Society awarded her its gold medal in 1828, and in 1835 she and Mary Somerville became its first honorary women members.
Benjamin Banneker, whose father had been enslaved and then freed, built a clock out of wood when he was 22, using a borrowed pocket watch as his model. It struck the hours and kept working for the rest of his life. In 1788 his friend George Ellicott lent him astronomy books and instruments, and at 57 Banneker taught himself enough mathematics and astronomy to predict eclipses. In 1791 he worked as an assistant on the survey of the new capital at Washington, and wrote to Thomas Jefferson, enclosing his almanac and pleading against slavery.
6A comet from a rooftop, then a fight for equal pay
On the tile: Maria Mitchell1847
On October 1, 1847, Nantucket-born Maria Mitchell was sweeping the sky from the roof of the Pacific Bank when she spotted a blurry object missing from her charts. The comet won her a gold medal from the King of Denmark. In 1865 she became professor of astronomy at the new Vassar College. Professors were paid 2,000 dollars, but she got 800, plus room and board for herself and her father. In 1871, after she and a colleague asked for equal pay, the trustees raised her salary to 2,500 dollars, then charged her 16 dollars a week for room and board.
7Thirty cents an hour and a key to cosmic distances
On the tile: Leavitt1912
In 1902 Harvard Observatory director Edward Pickering offered Henrietta Swan Leavitt a full-time job at thirty cents an hour, five cents above his usual rate. In 1908 she published a paper on 1,777 variable stars in the Magellanic Clouds and noted that the brighter ones had longer periods. In 1912 she reported this remarkable relation, a vital step toward measuring the distances to remote galaxies. In 1925 the mathematician Gösta Mittag-Leffler wrote to her, seriously inclined to nominate her for the Nobel Prize in Physics. He did not know she had died in 1921.
Georges Lemaître was a Belgian mathematician who had served as an artillery officer and was ordained a Catholic priest in 1923. In 1927 he published a paper in the Annales de la Société Scientifique de Bruxelles that derived what became known as Hubble's law, relating how fast a galaxy moves away to its distance. Edwin Hubble published considerably more evidence for an expanding universe in 1929. In October 2018, members of the International Astronomical Union voted, 78 percent in favor, to recommend a new name: the Hubble-Lemaître law.
As a Cambridge graduate student, Jocelyn Bell helped build a radio telescope from 120 miles of wire and cable on a four-acre field. In 1967 she noticed occasional bits of scruff in its data. She and her adviser, Antony Hewish, even considered signals from beings they called Little Green Men. She had discovered pulsars, rapidly spinning neutron stars. The discovery led to a Nobel Prize for Hewish. In 2018 she received a 3 million dollar Special Breakthrough Prize. "I reckon I've done pretty well out of not getting the Nobel Prize," she has said.
Galileo is often credited with inventing the telescope, but it was the work of craftsmen. In October 1608 the States General in The Hague considered patent applications for a tube with two lenses that magnified three or four times, first from Hans Lipperhey of Middelburg and then from Jacob Metius of Alkmaar. The officials found the device too easy to copy to award a patent. By April 1609 spyglasses were on sale in Paris. Galileo built his first that summer, and by late 1609 he had turned a twenty-powered instrument to the heavens.
In 1705 Edmond Halley used Isaac Newton's theories of gravity and planetary motion to argue that a comet seen in 1682 would come back, and he predicted its return in 1758. Halley had earlier paid out of his own pocket to publish Newton's Principia. He died in 1742, long before his prediction could be tested. On Christmas Day, 1758, the German astronomer Johann Georg Palitzsch spotted the comet. It returns about every 76 years, was last seen in 1986 and is due back in 2061.
People had seen stones fall from the sky long before 1803, but scientists typically doubted their stories. That changed after the early afternoon of April 26, 1803, when a shower of more than 3,000 stones fell around the town of L'Aigle in France. The French minister of the interior sent a young scientist, Jean-Baptiste Biot, to confirm the report. Biot questioned local people and compared the stones with the ground where they had landed. The L'Aigle fall proved to European scientists that rocks really do fall from the sky.
In September 1859 the English astronomer Richard Carrington saw a flare on the Sun with his own eyes. In the days that followed, powerful eruptions of solar material hit Earth head-on. Intense geomagnetic storms made telegraph lines spark worldwide, set fire to some telegraph offices and lit up northern lights as far south as Cuba. On July 23, 2012, a powerful eruption tore through Earth's orbit, and one researcher judged it at least as strong as the Carrington Event. Had it come one week earlier, Earth would have been in the line of fire.
Helium was found in sunlight before anyone found it on Earth. During a total solar eclipse in India in 1868, Pierre Janssen observed a new yellow line in the Sun's spectrum, the sign of an unknown element. Norman Lockyer recorded the same line and, assuming the new element was a metal, named it helium, from the Greek helios, meaning sun. In 1895 the chemist William Ramsay treated a uranium mineral with acid and examined the gas it gave off. In its spectrum he saw a bright yellow line matching the one from the Sun.
In the early 1900s most astronomers thought the Milky Way was the entire universe. In October 1923, using the 100-inch Hooker telescope at Mount Wilson, Edwin Hubble photographed the Andromeda nebula and marked three suspected novae with an N. One proved to be a Cepheid variable. He crossed out its N and wrote VAR, followed by an exclamation point. Its 31.4-day period put it 1 million light-years away, far beyond the Milky Way. Today's figure for Andromeda is 2.5 million. Reading Hubble's letter, Harlow Shapley reportedly said, "Here is the letter that destroyed my universe."
In the 1960s Vera Rubin and her colleague Kent Ford measured how fast stars and gas orbit in a nearby spiral galaxy. They expected the speeds to follow Newtonian gravity, with objects farther from the center orbiting more slowly. Instead, stars far out traveled as fast as those near the center. After observing dozens more galaxies by the 1970s, Rubin and colleagues concluded that each spiral galaxy is embedded in a halo of dark matter, material that gives off no light, holding 5 to 10 times as much mass as the visible galaxy.
When Carolyn and Gene Shoemaker and David Levy found a new comet on a photograph taken at Mount Palomar in March 1993, it was already in pieces. A close pass by Jupiter in July 1992 had torn it into more than 20 fragments, and they were on course to hit the planet. From July 16 to 22, 1994, they smashed into Jupiter's cloud tops. For the first time in history, NASA had spacecraft in position to watch a collision between two bodies in the solar system. The dark scars were eventually erased by Jupiter's winds.
In 1995 astronomers announced a planet around 51 Pegasi, a star much like our Sun. It was a gas giant, yet it raced around its star in just 4.2 days. It was the first exoplanet discovered around a Sun-like star. Thirty years later, in September 2025, the official count of exoplanets tracked by NASA reached 6,000, with a long list of candidates still waiting to be confirmed. New planets join the count on a rolling basis as scientists around the world confirm them, so no single world is considered number 6,000.