Category
Astronomy
Explore the 32 entries currently assigned to this category. These counts describe this curated catalogue, not the size or rate of change of the field itself.
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Not a fact anymore
The Milky Way is destined to collide and merge with the Andromeda galaxy.
What we know now
A future Milky Way–Andromeda merger remains plausible, but it is no longer considered inevitable. Simulations using newer Hubble and Gaia measurements, updated galaxy masses, and the gravitational influence of M33 and the Large Magellanic Cloud find roughly even odds that the two large galaxies will not merge within the next 10 billion years.
- Status
- Narrowed
- Category
- Astronomy
- Accepted for
- ≈13 years
- Changed approximately
- 2025
Not a fact anymore
Fomalhaut b is a directly imaged exoplanet.
What we know now
The source called Fomalhaut b is best explained as an expanding dust cloud produced by a collision between large planetesimals, not as a planet. Hubble watched the source fade, spread out, and move in a way consistent with dispersing collision debris.
- Status
- Reclassified
- Category
- Astronomy
- Accepted for
- ≈12 years
- Changed approximately
- 2020
Not a fact anymore
The Moon is completely dry.
What we know now
The Moon is extremely dry compared with Earth, but it is not water-free. Small amounts of water and hydroxyl are bound in lunar minerals and volcanic glass, and water ice exists in some permanently shadowed regions near the poles.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈39 years
- Changed approximately
- 1990s–2010s
Not a fact anymore
Pluto is the ninth planet of the Solar System.
What we know now
Under the International Astronomical Union's 2006 definition, Pluto is a dwarf planet because it has not cleared the neighbourhood around its orbit. The Solar System has eight objects formally classified as planets.
- Status
- Reclassified
- Category
- Astronomy
- Accepted for
- ≈76 years
- Changed approximately
- 2006
Not a fact anymore
The expansion of the universe is slowing down under the gravitational pull of matter.
What we know now
Observations of distant Type Ia supernovae show that the expansion of the universe is accelerating. The cause is described as dark energy, although its physical nature remains unknown.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈48 years
- Changed approximately
- 1998
Not a fact anymore
Gamma-ray bursts come from neutron stars within the Milky Way.
What we know now
Most gamma-ray bursts are enormous explosions in distant galaxies, not ordinary events inside the Milky Way. Long bursts are linked to the collapse of massive stars, while many short bursts come from mergers of compact objects such as neutron stars.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈22 years
- Changed approximately
- 1991–1997
Not a fact anymore
Saturn is the only planet with rings.
What we know now
All four giant planets in our solar system have rings. Jupiter, Uranus, and Neptune have much fainter systems than Saturn.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈327 years
- Changed approximately
- 1977–1989
Not a fact anymore
Black-hole solutions were widely regarded as mathematical idealizations rather than realistic outcomes of gravitational collapse in nature.
What we know now
Black holes are real astrophysical objects. Evidence comes from stellar and gas motions, accretion radiation, gravitational waves, and horizon-scale imaging, and black holes occur across a wide range of masses.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- 1960s–1970s
Not a fact anymore
Mars is crossed by a planet-wide network of long, straight canals visible from Earth.
What we know now
Spacecraft imagery shows no artificial or geometrically straight canal network. Mars has natural valleys, channels, fractures, dunes, and evidence of ancient flowing water, but not the telescopic canal system once mapped.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈80 years
- Changed approximately
- Early 20th century–1960s
Not a fact anymore
Mercury keeps the same face permanently pointed toward the Sun.
What we know now
Mercury rotates three times for every two orbits around the Sun. It is in a 3:2 spin-orbit resonance, so every part of the planet experiences daylight over time.
- Status
- Corrected
- Category
- Astronomy
- Accepted for
- ≈80 years
- Changed approximately
- 1965–1966
Not a fact anymore
Quasars are unusual stars within or near the Milky Way.
What we know now
Quasars are not stars. They are extraordinarily bright active galactic nuclei—the compact centers of distant galaxies—powered by matter falling toward supermassive black holes.
- Status
- Reclassified
- Category
- Astronomy
- Accepted for
- ≈5 years
- Changed approximately
- 1963 onward
Not a fact anymore
The Sun's outer atmosphere must be cooler than its visible surface.
What we know now
The Sun's corona, its thin outer atmosphere, reaches roughly one to several million kelvin—far hotter than the visible surface below, which is about 5,800 K. The corona is extremely thin, so high temperature does not mean it contains more total heat than the denser layers beneath it.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈90 years
- Changed approximately
- 1939–1942
Not a fact anymore
The Sun is powered by ordinary chemical burning.
What we know now
The Sun is powered by nuclear fusion. In its core, hydrogen nuclei combine to form helium, converting a small amount of mass into energy.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- ≈188 years
- Changed approximately
- 19th century–1930s
Not a fact anymore
The universe is static and does not expand.
What we know now
The universe is expanding on large scales. Distant galaxies generally recede in a relationship between their distance and redshift, and the expansion rate has changed over cosmic time.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈79 years
- Changed approximately
- 1920s–1930s
Not a fact anymore
Stars have roughly the same elemental composition as Earth.
What we know now
Most ordinary stars are made overwhelmingly of hydrogen and helium, not an Earth-like mixture of heavy elements. Elements such as iron, calcium, and oxygen are present in much smaller proportions, and their abundances vary between stars.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈40 years
- Changed approximately
- 1925–1929
Not a fact anymore
The Milky Way contains essentially the entire universe.
What we know now
The Milky Way is one galaxy among an enormous population of other galaxies spread throughout the observable universe.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈40 years
- Changed approximately
- 1920s
Not a fact anymore
The Sun shines only because gravity is slowly making it contract.
What we know now
Gravitational contraction helped heat the young Sun, but the present Sun is powered mainly by nuclear fusion in its core.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- ≈70 years
- Changed approximately
- 1920s–1930s
Not a fact anymore
The Sun lies at or near the center of the Milky Way.
What we know now
The Sun lies in the Milky Way's disk, roughly 26,000 light-years from the galactic center, and takes about 240 million years to complete one orbit.
- Status
- Corrected
- Category
- Astronomy
- Accepted for
- ≈168 years
- Changed approximately
- 1910s–1930s
Not a fact anymore
Stars can be treated as essentially fixed stellar types rather than objects passing through connected evolutionary stages.
What we know now
Stars form, change structure and luminosity over time, and end in mass-dependent final states. Stellar classes occupy different stages and tracks of stellar evolution rather than being permanently fixed kinds.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- Late 19th–mid-20th century
Not a fact anymore
The space between stars contains no detectable material medium.
What we know now
Interstellar space contains an extremely thin interstellar medium: gas, plasma, dust, molecules, cosmic rays, and magnetic fields. Denser molecular clouds are the raw material for new stars and planets.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- 1904–1920s
Not a fact anymore
Saturn's rings are solid, continuous structures.
What we know now
Saturn's rings consist of enormous numbers of independently orbiting particles, mostly water ice, ranging from dust-sized grains to large blocks and embedded moonlets.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈204 years
- Changed approximately
- 1850s–1895
Not a fact anymore
Stones do not fall from the sky; reported meteorite falls are mistaken, fraudulent, or terrestrial.
What we know now
Meteorites are solid extraterrestrial objects that survive passage through the atmosphere and reach Earth's surface. Their origins include asteroids, the Moon, and Mars.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈78 years
- Changed approximately
- 1790s–1803
Not a fact anymore
Saturn is the outermost planet in the planetary system.
What we know now
Saturn is the sixth planet from the Sun. Uranus and Neptune orbit farther out, along with many trans-Neptunian dwarf planets and smaller bodies.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈1,631 years
- Changed approximately
- 1781–1783
Not a fact anymore
The fixed stars do not move relative to one another.
What we know now
Stars move through the Milky Way. Their slow change in position across the sky is called proper motion and can be measured by astrometry. Constellations therefore change gradually over long timescales.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈1,588 years
- Changed approximately
- 1738 (first statistically significant stellar proper-motion evidence)
Not a fact anymore
Heavenly bodies are made from a special incorruptible substance called aether or quintessence, rather than the matter found on Earth.
What we know now
The Sun, stars, planets, moons, asteroids, and comets are made from the same chemical elements and governed by the same fundamental physics studied on Earth, although their compositions and physical states differ.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- 17th–19th centuries
Not a fact anymore
Earth stands motionless at the center while the Sun, planets, and stars revolve around it.
What we know now
Earth rotates once each day and orbits the Sun once each year. The other planets also orbit the Sun, while the solar system itself orbits within the Milky Way.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- ≈1,460 years
- Changed approximately
- 16th–17th centuries
Not a fact anymore
The Milky Way is a phenomenon of the upper terrestrial atmosphere rather than the combined light of distant stars.
What we know now
The Milky Way is our galaxy, a vast gravitationally bound system containing hundreds of billions of stars along with gas, dust, dark matter, and a central supermassive black hole.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈1,960 years
- Changed approximately
- Early telescopic astronomy
Not a fact anymore
The planets travel around the Sun in perfect circles.
What we know now
Planets move around the Sun in ellipses, with the Sun at one focus. Many planetary orbits are nearly circular, but they are not required to be perfect circles.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- ≈66 years
- Changed approximately
- 1605–1609
Not a fact anymore
Comets are temporary phenomena within Earth's atmosphere rather than distant celestial bodies.
What we know now
Comets are small solar-system bodies, largely composed of ice, dust, and rock, that orbit the Sun. Their visible comae and tails develop when they approach the Sun.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈1,927 years
- Changed approximately
- 1577–17th century
Not a fact anymore
The planets and stars are carried around Earth by real nested celestial spheres.
What we know now
Planets and smaller bodies move through space under gravity and inertia; no solid or crystalline shells carry them around Earth.
- Status
- Superseded
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- Late 16th–17th centuries
Not a fact anymore
The heavens above the Moon are eternal, incorruptible, and cannot undergo genuine physical change.
What we know now
Celestial objects form, evolve, erupt, collide, and die. Stars change over time, the Sun has active surface phenomena, comets move through planetary space, and transient events occur throughout the universe.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- ≈1,922 years
- Changed approximately
- 1572–early 17th century
Not a fact anymore
The Earth is flat, and its broad surface remains suspended because the air beneath it supports it.
What we know now
Earth is an oblate spheroid: nearly spherical, slightly flattened at the poles, and held together by gravity rather than supported by air beneath a flat surface.
- Status
- Overturned
- Category
- Astronomy
- Accepted for
- Not quantified
- Changed approximately
- By the 4th century BCE in Greek learned astronomy
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