“The earth is flat”

• At human scale the local surface of the Earth appears essentially flat: the curvature of a ~6,371 km radius sphere drops only about 8 cm over 1 km, so everyday visual experience and short-range surveying are consistent with a flat plane. This is why flat-Earth intuition persists, but it is an artifact of scale, not evidence of global geometry.
• Flat-Earth advocates cite apparent anomalies such as distant objects visible over water, long-range photographs, and 'no felt motion.' These are explained by atmospheric refraction, the small angular size of curvature at short distances, and the fact that constant velocity produces no sensation of motion — they do not survive quantitative analysis.
• No other substantive evidence supports the claim; the arguments offered in its favor are misinterpretations of observations that the spherical model predicts correctly.

• Direct imaging: thousands of whole-Earth photographs from Apollo (e.g., the 1972 'Blue Marble'), and continuous full-disk imagery from NASA's DSCOVR/EPIC camera at the Sun–Earth L1 point, show a rotating sphere with a visible terminator; independent imagery exists from ESA, JAXA, ISRO, Roscosmos, CNSA and commercial operators.
• Eratosthenes measured Earth's circumference around 240 BCE from differing solar shadow angles at Alexandria and Syene, getting within a few percent of the modern value — a result that is impossible on a flat plane with a distant Sun and requires an implausible ad hoc nearby-Sun geometry to mimic.
• Geodesy and satellite navigation: GPS, GLONASS and Galileo compute positions using an oblate-spheroid reference model (WGS 84). Meter-level positioning worldwide would fail immediately if the underlying shape model were wrong.
• Circumnavigation and flight/shipping routes: great-circle paths (e.g., polar routes between North America and Asia) are shortest only on a sphere, and flight times match spherical distances, not any flat-Earth map projection.
• Astronomical observations: different constellations are visible from different latitudes, Polaris's altitude equals the observer's latitude, the Southern Cross is invisible from mid-northern latitudes, and time zones/sunrise offsets follow from a rotating sphere.
• Lunar eclipses always project a round Earth shadow on the Moon regardless of the Earth's orientation — only a sphere casts a circular shadow from every direction.
• Measured gravity behaves as expected for a spherical mass: g varies slightly with latitude and altitude as predicted by the oblate spheroid, and the Foucault pendulum and Coriolis deflection demonstrate rotation about an axis.
• Flat-Earth models make no successful quantitative predictions and cannot account for eclipse timing, satellite orbits, seasons, or the existence of the 24-hour Antarctic summer sun; the claim has been repeatedly and exhaustively debunked yet continues to circulate.

99/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASA Science – Earthgov · 98 · NASA Goddard – DSCOVR EPIC full-disk Earth imagerygov · 97 · NASA Visible Earth ('The Blue Marble')gov · 96 · Encyclopaedia Britannicaother · 85 · Wikipediaother · 75 · Wikipediaother · 72

• Local, everyday observations can make Earth seem flat: over short distances the curvature is very small, so roads, fields, lakes, and the sea horizon can appear level to an unaided observer.
• Some people cite the horizon appearing flat or water surfaces being 'level' as support, but these are observations of local scale and do not distinguish a flat Earth from a very large curved Earth.

• Government geodesy and ocean-science sources describe Earth as an oblate spheroid/ellipsoid, not a plane; its equatorial diameter is slightly larger than its polar diameter.
• Space-based observation directly shows Earth as a globe, including full-disk imagery from Apollo missions and modern weather/observing satellites.
• Earth’s measurable curvature explains phenomena such as ships disappearing hull-first over the horizon, different star visibility by latitude, and the ability to circumnavigate in many directions.
• Time zones, seasons, satellite orbits, GPS, eclipses, and global navigation all depend on and repeatedly confirm a roughly spherical Earth; a flat-Earth model does not coherently account for these observations.
• The claim has been repeatedly debunked by scientific and fact-checking sources and is contradicted by centuries of measurements, navigation, astronomy, and modern satellite data.

99/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NOAA National Ocean Servicegov · 98 · NASA Sciencegov · 98 · NASA Visible Earthgov · 96

• From a localized human vantage point at ground level, the Earth's horizon appears flat to the naked eye, leading to intuitive sensory assumptions.
• Water in localized, relatively small basins appears to rest entirely flat; proponents erroneously scale this observation up to conclude that global oceans must also be on a flat plane.
• Certain historical line-of-sight experiments over short distances (such as the Bedford Level experiment) yielded results that seemed to show a lack of curvature, though these observations were actually the result of atmospheric refraction.

• Decades of direct photographic and video evidence from satellites, space probes, the International Space Station, and Apollo missions definitively depict Earth as a sphere (specifically an oblate spheroid).
• Ships traversing the ocean disappear hull-first over the horizon, a visual phenomenon caused by the curvature of the Earth.
• During a lunar eclipse, the shadow cast by the Earth on the Moon is consistently curved, an observation originally noted by ancient Greek astronomers as proof of a spherical planet.
• Observers in the Northern and Southern Hemispheres see entirely different sets of stars and constellations, which is only possible if they are looking outward from different angles on a sphere.
• The physical laws of gravity dictate that large, massive objects pull matter toward their center of mass, naturally forcing planets to form into spherical shapes.
• The Coriolis effect, the way prevailing winds and ocean currents curve, is a direct result of the Earth's spherical shape and its rotation.
• Global navigation networks, commercial aviation flight paths, and GPS technology are entirely predicated on a spherical Earth model and function with pinpoint accuracy globally.

100/100 — the lab’s own confidence in the score above, not a second reading of the claim.

National Oceanic and Atmospheric Administration (NOAA)gov · 100 · NASA Goddard Space Flight Centergov · 100

• The claim is not supported by reliable empirical evidence. The strongest commonly cited point in its favor is that the ground and horizon can appear locally flat because Earth is extremely large relative to human viewing distances; this is an observation about local appearance, not evidence that the planet is globally flat.
• Some flat-Earth proponents dispute photographs from space and argue that curvature is not obvious in ordinary photographs. These objections challenge particular observations but do not provide a coherent, quantitatively predictive model that explains geodesy, satellite navigation, global time zones, eclipses, and long-distance travel better than the oblate-spheroid model.

• NOAA states that Earth is an irregularly shaped ellipsoid: slightly wider at the equator because of rotation, and it describes geodesy as the measurement of Earth's size and shape.[1]
• NOAA's geodesy tutorial describes Earth as nearly spherical, slightly flattened at the poles and bulging at the equator, and notes that this model matches measured observations.[2]
• NASA documents photographic and observational evidence of Earth's curvature, including high-altitude balloon photography and the curvature visible from elevated viewpoints.[3]
• Modern geodesy uses gravity measurements, satellite positioning, radio telescopes, and long-range lasers to measure Earth's shape and surface to high precision; these systems are consistent with an oblate spheroid or geoid, not a flat plane.[4][5]
• The observed curved shadow of Earth during lunar eclipses, changing star visibility with latitude, circumnavigation, global time zones, and satellite orbits are mutually consistent with a roughly spherical Earth and incompatible with a flat Earth without ad hoc explanations.
• The technically precise conclusion is that Earth is not a perfect sphere: it is approximately an oblate spheroid with an irregular geoid. That qualification does not support the statement that Earth is flat.

99/100 — the lab’s own confidence in the score above, not a second reading of the claim.

National Oceanic and Atmospheric Administrationgov · 99 · National Oceanic and Atmospheric Administrationgov · 99 · National Aeronautics and Space Administrationgov · 99 · National Oceanic and Atmospheric Administrationgov · 99 · National Oceanic and Atmospheric Administrationgov · 98 · Encyclopaedia Britannicaother · 94

• The ground and horizon look locally flat to the unaided eye because Earth's radius is ~6,371 km, so curvature is not obvious over everyday distances.
• Flat-Earth advocates cite the 1838 Bedford Level canal experiment and similar amateur sight-lines over water; those appearances are produced by atmospheric refraction and limited baselines, not a planar Earth.
• Remaining 'for' arguments are institutional-distrust claims (e.g., that space imagery is fabricated), not independent geometric or physical measurements.

• Satellite geodesy and NASA planetary data give an oblate spheroid: equatorial radius ~6378.1 km, polar radius ~6356.8 km, flattening ~1/298.3—incompatible with a disk.
• Apollo, ISS, and operational weather/remote-sensing satellites continuously image a round Earth (e.g., Apollo 17 Blue Marble).
• Lunar eclipses show a round Earth shadow; ships go hull-down on the horizon; visible constellations and solar elevation change with latitude; circumnavigation and time zones match a rotating sphere.
• Eratosthenes measured Earth's circumference ~240 BCE from sun-angle differences; GNSS, satellite laser ranging, and gravity missions (GRACE/GOCE) recover the same ellipsoidal figure.
• Navigation, GPS, the Foucault pendulum, and the Coriolis effect all require a spherical rotating Earth; a flat model cannot fit these observations together.

100/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASA Goddard NSSDCAgov · 98 · NASA Visible Earthgov · 98 · NASA Earth Observatorygov · 98 · Encyclopaedia Britannicaother · 92