31 entries
Astronomy & Space
Planets demoted, new worlds found, and a universe that keeps getting bigger and stranger than the one on your classroom poster.
Changes here run from 1989 to 2026.
- Disproved14
- Updated12
- Refined3
- Reclassified2
- DisprovedNot in textbooks yet
TaughtFinding a new asteroid, or catching a supernova as it flares, is painstaking work: an astronomer comparing images, spotting a moving dot or a new point of light, confirming it night by night. Discoveries come in ones and tens, and the vast majority of the sky's changes pass unseen.
NowOn 30 June 2026, the NSF–DOE Vera C. Rubin Observatory began its 10-year Legacy Survey of Space and Time, imaging the entire southern sky every few nights. In just six weeks of early optimization runs it had already found over 11,000 new asteroids, and in full operation it issues up to about 7 million alerts of changes in the sky every single night.
- UpdatedNot in textbooks yet
A day on Uranus is 17 hours and 14 minutes long
Changed in2025TaughtUranus rotates once every 17 hours and 14 minutes. Voyager 2 measured it during its 1986 flyby by timing the planet's radio emissions and magnetic field, and that has been the figure ever since.
NowIn April 2025, using a decade of Hubble observations of Uranus's auroras, astronomers pinned the rotation period at 17 hours, 14 minutes and 52 seconds: about 28 seconds longer than Voyager's value, and a thousand times more precise.
- UpdatedNot in textbooks yet
TaughtInterstellar visitors are vanishingly rare. We have seen exactly two objects confirmed to come from beyond our solar system: 'Oumuamua in 2017 and comet Borisov in 2019. Catching a third is a someday hope.
NowOn 1 July 2025 the NASA-funded ATLAS survey spotted 3I/ATLAS, the third confirmed interstellar object, a comet on a wildly hyperbolic orbit that could only have come from another star system.
- UpdatedNot in textbooks yet
Saturn has 82 moons
Changed in2025TaughtSaturn is the moon champion of the solar system with 82 moons, having narrowly overtaken Jupiter. That is the tidy, memorizable number for the ringed planet's family.
NowIn March 2025 the International Astronomical Union recognized 128 newly confirmed moons of Saturn in one stroke, bringing its total to 274, more than every other planet in the solar system combined.
- UpdatedNot in textbooks yet
TaughtOur galaxy and the Andromeda galaxy are falling toward each other and will smash together in roughly 4.5 billion years, merging into a single giant elliptical galaxy sometimes nicknamed 'Milkomeda.' It is a certainty, just a distant one.
NowA June 2025 study in Nature Astronomy ran 100,000 simulations with the latest Gaia and Hubble data and found only about a 50-50 chance the two galaxies collide within the next 10 billion years. The head-on merger is no longer a sure thing.
- Updated
Nothing humanmade can survive flying close to the Sun
Changed in2024TaughtThe Sun's surface is thousands of degrees, and its corona is hotter still. Any spacecraft that ventured near it would be destroyed, so our star can only ever be studied from a safe distance.
NowOn 24 December 2024, NASA's Parker Solar Probe passed just 3.8 million miles from the Sun's surface (flying through the corona at about 430,000 mph, the closest and fastest any human-made object has ever come to a star) and radioed home days later, intact.
- Disproved
TaughtSoft-landing on the Moon is so hard that only three superpowers (the United States, the Soviet Union, and China) have ever managed it. A soft landing is a feat of national space programs, not something a private company can do.
NowOn 22 February 2024, Intuitive Machines' Odysseus lander touched down near the Moon's south pole: the first soft landing on the Moon by a privately built spacecraft, and the first American landing of any kind since Apollo 17 in 1972.
- Disproved
No spacecraft has ever landed near the Moon's south pole
Changed in2023TaughtEvery Moon landing (Apollo, the Soviet and Chinese landers) touched down in the relatively flat, easy terrain near the equator. The south polar region, with its rugged shadows and craters that may hold water ice, was a place probes flew over or crashed into, never a place anyone had softly landed.
NowOn 23 August 2023, India's Chandrayaan-3 lander touched down at about 69° south: the first soft landing anywhere near the lunar south pole, and the fourth country ever to land on the Moon.
- Disproved
TaughtLIGO can catch the sharp chirp of two black holes merging nearby, but the deep background hum (the overlapping ripples of countless supermassive black holes across all of cosmic history, stretching spacetime over years and decades) is far too slow and too faint for any instrument to pick out.
NowIn June 2023, the NANOGrav collaboration and three other pulsar-timing arrays announced compelling evidence for exactly that background: a sea of nanohertz gravitational waves, most likely from supermassive black-hole binaries, detected by watching pulsars scattered across the galaxy tick out of sync.
- Disproved
TaughtThe dinosaurs had no defense against the asteroid that killed them, and neither would we. If a large one were found on a collision course, our only real options would be to evacuate and hope. Actually deflecting one is science fiction.
NowOn 26 September 2022 NASA's DART spacecraft deliberately crashed into the asteroid moonlet Dimorphos and measurably changed its orbit, shortening it by about 32 minutes. It was the first time humanity has altered the motion of a celestial body on purpose.
- Updated
TaughtOur deepest look into the cosmos is the Hubble Space Telescope's Deep Field: a tiny patch of sky stared at for days, revealing thousands of distant galaxies. It is the benchmark image of how far back we can see.
NowOn 11 July 2022, NASA released Webb's First Deep Field of the cluster SMACS 0723: the deepest and sharpest infrared image of the universe ever taken, reaching fainter and earlier galaxies than Hubble's deepest fields, in about 12.5 hours rather than weeks.
- Disproved
TaughtA supermassive black hole, Sagittarius A*, sits at the center of the Milky Way; we know it from the orbits of stars whipping around something invisible. But it is 27,000 light-years away and, by definition, emits no light, so an actual image of it is impossible.
NowOn 12 May 2022, the Event Horizon Telescope collaboration released the first image of Sagittarius A*: a glowing ring of superheated gas encircling the dark shadow of the black hole itself, direct visual confirmation of the object at our galaxy's heart.
- Disproved
Only professionally trained astronauts can go to orbit
Changed in2021TaughtReaching Earth orbit takes years of professional astronaut training and the backing of a national space agency. The handful of 'space tourists' who went before all flew to a space station alongside career cosmonauts; a crew of ordinary civilians orbiting on their own is not something that happens.
NowFrom 15–18 September 2021, SpaceX's Inspiration4 mission put four private citizens, none of them professional astronauts, into orbit for three days aboard a Crew Dragon, with no career astronaut on board. It was the first all-civilian orbital spaceflight.
- Updated
Only the United States has ever operated a rover on Mars
Changed in2021TaughtLanding and driving a rover on Mars is so hard that only NASA has ever done it. The Soviet Union and later Russia lost lander after lander; Mars's surface was, in practice, an American-only club.
NowOn 22 May 2021, China's Zhurong rover rolled onto the surface of Utopia Planitia, making China the second nation ever to operate a rover on Mars, and the first to orbit, land, and deploy a rover all on its first attempt.
- Disproved
Powered flight is impossible in Mars's thin atmosphere
Changed in2021TaughtMars's atmosphere is only about 1% as dense as Earth's, far too thin for wings or rotors to get a grip. A helicopter or airplane could never generate enough lift to fly there. Mars is explored by rovers on the ground, and always will be.
NowOn 19 April 2021, NASA's Ingenuity helicopter lifted off, hovered, and landed on Mars: the first powered, controlled flight by an aircraft on another world. It went on to fly 72 times over nearly three years, far outlasting its planned five flights.
- Disproved
Betelgeuse's sudden dimming means it is about to explode
Changed in2020TaughtWhen Betelgeuse, the red shoulder of Orion, lost two-thirds of its brightness over the winter of 2019–2020, the natural reading was that the old supergiant was finally about to die, that we were watching the prelude to a supernova bright enough to cast shadows on Earth.
NowIn August 2020, Hubble observations showed the Great Dimming was a dust cloud, not a death rattle. The star had belched a huge bubble of hot plasma from its surface; as it drifted outward it cooled into dust that briefly veiled part of the star. By April 2020 Betelgeuse had already brightened back to normal.
- Updated
Nobody knows what causes fast radio bursts
Changed in2020TaughtFast radio bursts, millisecond flashes of radio energy that release more power than the Sun does in days, were one of astronomy's great open mysteries. Every one had come from a distant galaxy, too far to trace to any particular object, and their source was genuinely unknown.
NowOn 28 April 2020, telescopes caught a fast radio burst coming from inside our own galaxy, from SGR 1935+2154, a magnetar about 30,000 light-years away. It was the first FRB ever tied to a known object, showing that at least some of these bursts are flares from the crushingly strong magnetic fields of dead stars.
- Refined
TaughtBlack holes are predicted by general relativity and the indirect evidence is suggestive, but by definition light cannot escape one, so we will never actually image one.
NowThe Event Horizon Telescope released the first image of a black hole's shadow, in galaxy M87, in April 2019, and one of Sagittarius A* at our own galaxy's center in 2022.
- Refined
Gravitational waves are predicted but undetectable
Changed in2016TaughtEinstein predicted ripples in spacetime, but they are so faint that detecting one is probably beyond any instrument we could build.
NowLIGO detected gravitational waves from two merging black holes on 14 September 2015, announced in February 2016. Detections are now routine, with hundreds recorded.
- Updated
Pluto is a blurry smudge and always will be
Changed in2015TaughtPluto is too small and too far for us to see any detail. The best image is a handful of fuzzy pixels from Hubble.
NowNASA's New Horizons flew past Pluto in July 2015 and returned sharp images of nitrogen glaciers, water-ice mountains, and a haze-layered atmosphere.
- Updated
No human object has left the solar system
Changed in2013TaughtVoyager 1 is heading out of the solar system and will eventually cross into interstellar space, sometime in the distant future.
NowVoyager 1 crossed the heliopause in August 2012, confirmed by NASA in September 2013. Voyager 2 followed in 2018. Both are now in interstellar space.
- Disproved
The Moon is completely dry
Changed in2009TaughtApollo samples showed the Moon is bone dry. There is no water there in any form.
NowThere is water ice in permanently shadowed polar craters, confirmed when NASA's LCROSS mission deliberately crashed into Cabeus crater in 2009, and water molecules exist even on the sunlit surface.
- Disproved
Mars is a dry, dead world with no water
Changed in2008TaughtMars might have had water long ago, but today it is a dry desert. Any water is speculation.
NowMars Odyssey detected vast subsurface hydrogen in 2002, and NASA's Phoenix lander physically touched and identified water ice in the Martian soil in 2008. There is enough ice at the poles to cover the planet in a global ocean meters deep.
- Updated
The Milky Way has four spiral arms
Changed in2008TaughtOur galaxy is a four-armed spiral, and there is a diagram in the back of the book showing exactly where we sit in one of them.
NowData from NASA's Spitzer Space Telescope showed the Milky Way has two dominant spiral arms of stars, Scutum-Centaurus and Perseus, plus minor arms and spurs. It is also a barred spiral.
- Reclassified
Ceres is the largest asteroid
Changed in2006TaughtBetween Mars and Jupiter lies the asteroid belt, and the biggest rock in it is Ceres.
NowThe same 2006 IAU resolution that demoted Pluto promoted Ceres. It is round under its own gravity, so it is a dwarf planet.
- Reclassified
Pluto is the ninth planet
Changed in2006TaughtThe solar system has nine planets, and the ninth and smallest is Pluto.
NowIn 2006 the International Astronomical Union defined the word "planet" for the first time, and Pluto did not meet the third criterion. It is now a dwarf planet. The solar system has eight planets.
- Refined
The universe is 10 to 20 billion years old
Changed in2003TaughtThe universe is somewhere between 10 and 20 billion years old. Estimates vary widely and astronomers disagree.
Now13.8 billion years, known to better than 1%. WMAP delivered the first precise figure in 2003; Planck refined it in 2013.
- Updated
The universe is made of the stuff on the periodic table
Changed in2003TaughtEverything in the universe is made of atoms: the elements in the periodic table, arranged into stars, planets, and people.
NowOrdinary atomic matter is about 5% of the universe's energy content. Roughly 27% is dark matter and 68% is dark energy, and we do not know what either is.
- Disproved
The universe's expansion is slowing down
Changed in1998TaughtThe universe has been expanding since the Big Bang, and gravity is gradually slowing that expansion. The open question is whether it slows enough to collapse again.
NowTwo teams studying distant supernovae found in 1998 that the expansion is accelerating. The cause, called dark energy, appears to make up roughly 68% of the universe.
- Disproved
No planets have been found outside our solar system
Changed in1995TaughtOther stars may have planets, but we have never detected one, and we may never be able to.
NowThe first planet confirmed orbiting a Sun-like star, 51 Pegasi b, was announced in 1995. More than 6,000 exoplanets have been confirmed since.
- Disproved
Saturn is the only planet with rings
Changed in1989TaughtSaturn is unique in the solar system: it is the one planet with a ring system.
NowAll four giant planets have rings. Uranus's were found in 1977, Jupiter's by Voyager 1 in 1979, and Neptune's rings were confirmed by Voyager 2 in 1989.