“Earth is an oblate spheroid, slightly wider at the equator than from pole to pole.”

• NASA's planetary fact sheet gives Earth's equatorial radius as 6,378.137 km and polar radius as 6,356.752 km — a difference of about 21.4 km — with a flattening of 0.00335 (≈1/298.26), exactly the oblate-spheroid geometry described in the claim.
• The globally adopted geodetic reference frame, WGS 84 (used by GPS), models Earth as an oblate ellipsoid of revolution with semi-major axis 6,378,137 m and inverse flattening 298.257223563; GRS 80 is nearly identical. Satellite navigation would not function to centimeter precision if this shape model were wrong.
• The equatorial bulge is the physically expected result of rotation: centrifugal effect at the equator opposes gravity, an argument made by Newton and confirmed in the 18th century by the French geodetic arc-measuring expeditions to Lapland and Peru, which found meridian degrees longer near the pole than near the equator.
• Independent modern measurements — satellite laser ranging, GRACE/GOCE gravity missions, VLBI, and direct orbital tracking (the J2 gravitational coefficient) — all converge on the same ~1/298 flattening, i.e., wider across the equator than pole to pole.
• NOAA and other geodetic agencies routinely describe Earth's reference shape as an oblate ellipsoid/spheroid, using it as the baseline against which the more irregular geoid is measured.
• Consequence checks agree: sea-level points on the equator are ~21 km farther from Earth's center than the poles, which is why Chimborazo/Cayambe (near the equator), not Everest, are the summits farthest from Earth's center.

• Strictly speaking, Earth is not a perfect oblate spheroid: the true equipotential surface (the geoid) departs from the best-fit ellipsoid by roughly -100 m to +85 m (e.g., the Indian Ocean low, the New Guinea high), so 'oblate spheroid' is an idealized model rather than an exact description.
• Satellite geodesy shows small higher-order asymmetries — the odd zonal harmonic J3 gives a slight 'pear shape' with the South Pole a few tens of meters closer to the reference ellipsoid than the North Pole, and the equator itself is very slightly elliptical (a few hundred meters).
• Solid topography adds larger local deviations (Everest ~8.8 km up, ocean trenches ~11 km down), and tides, post-glacial rebound and mass redistribution make the shape slightly time-variable.
• None of these refinements contradict the claim's substance; they are second-order corrections to a shape that is, to first order, an oblate spheroid with an equatorial bulge. The word 'slightly' in the claim is well chosen: the ~0.3% flattening means Earth would look round to the eye from space.

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

NASA Goddard Space Flight Center / NSSDCgov · 99 · NASA Sciencegov · 97 · NOAA National Ocean Servicegov · 95 · NOAA National Geodetic Surveygov · 94 · NASA Space Placegov · 90 · European Space Agency (GOCE gravity mission)gov · 93 · Encyclopaedia Britannicaother · 82

• Direct geodetic/astronomical measurements list Earth's equatorial radius (6,378.137 km) as larger than its polar radius (6,356.752 km), which means Earth is wider around the equator than from pole to pole.
• NASA's Earth facts similarly give an equatorial diameter of about 12,756 km and a polar diameter of about 12,714 km, confirming the small equatorial bulge.
• The physical explanation is well established: Earth's rotation produces centrifugal effects that make the planet slightly flattened at the poles and bulged at the equator, the defining feature of an oblate spheroid.

• The claim is a simplified description: Earth is not a mathematically perfect oblate spheroid. For precise surveying, agencies use reference ellipsoids and the geoid because Earth has irregular mass distribution, topography, ocean variation, and small deviations from a smooth spheroid.
• Those refinements do not contradict the statement as written; they only add precision. At planetary scale, 'oblate spheroid, slightly wider at the equator than from pole to pole' is substantially accurate.

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

NASA Goddard Space Flight Center / NSSDCgov · 99 · NASAgov · 98 · NOAA National Ocean Servicegov · 96

• Geodetic measurements, satellite data, and space observations overwhelmingly confirm that Earth's equatorial radius (approximately 6,378 km) is larger than its polar radius (approximately 6,356 km).
• This difference of about 22 kilometers in radius is caused by the centrifugal force generated by Earth's rotation, which pushes matter outward near the equator, creating an equatorial bulge.
• Major scientific and governmental organizations, including NASA and NOAA, define the Earth's macroscopic shape as an oblate spheroid (or ellipsoid) based on continuous global positioning system (GPS) and gravity anomaly satellite (GRACE) measurements.

• In highly precise pedantic terms, Earth is not a mathematically perfect oblate spheroid. Due to variations in gravitational pull, mass distribution, and topographical features (mountains and ocean trenches), its true exact shape is best described as a 'geoid'—a slightly lumpy, irregular ellipsoid.
• Claims completely counter to the oblate spheroid model, such as Flat Earth theories, exist but entirely lack empirical evidence and are contradicted by centuries of established physics, astronomy, and direct observation.

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

NASA Goddard Space Flight Centergov · 100 · National Oceanic and Atmospheric Administration (NOAA)gov · 98 · Scientific Americannews · 95

• Earth is conventionally modeled as an oblate spheroid: NOAA’s National Geodetic Survey states that its equatorial radius is larger than its polar radius.[source 2]
• NASA reports an equatorial radius of about 6,378 km and a polar radius of about 6,357 km, meaning Earth is slightly flattened at the poles.[source 7]
• NOAA explains that Earth is wider at the equator than at the poles, consistent with the claim.[source 1]
• A peer-reviewed study describes the rotating Earth as oblate, with a smaller pole-to-pole dimension and a bulging equatorial region; it gives an equatorial–polar radius difference of roughly 21 km.[source 13]

• No credible scientific evidence in the reviewed sources contradicts the claim.
• The wording is an approximation: Earth’s actual physical surface is irregular and is more precisely represented by a geoid, while an oblate spheroid is a simplified reference model. This does not make the central statement false.
• The phrase “wider at the equator” refers to diameter or radius through Earth’s center, not necessarily to every local surface measurement; topography and the geoid introduce smaller regional deviations.

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

NOAA National Geodetic Surveygov · 99 · NASA Goddard Space Flight Centergov · 99 · NOAA Ocean Servicegov · 97 · Comptes Rendus Geosciencejournal · 94

• Geodetic and satellite measurements show Earth's equatorial radius is ~6378.137 km versus polar radius ~6356.752 km (difference ~21 km in radius, ~43 km in diameter), making it wider at the equator.
• Rotation produces a centrifugal effect that is strongest at the equator, producing the well-measured equatorial bulge; this is the defining geometry of an oblate spheroid.
• Standard planetary fact sheets and geodesy references (NASA, IERS-derived models) classify Earth's figure as an oblate spheroid to first order.

• Earth's actual equipotential surface (the geoid) includes smaller higher-order terms (slight north-south asymmetry sometimes called a pear shape, plus topography and local gravity anomalies), so it is not a mathematically perfect oblate spheroid.

96/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASA Goddard Space Flight Centergov · 98 · Wikipediaother · 82 · Encyclopaedia Britannicaother · 90