Empirical Earth · Shape, Curvature & the Horizon

The “1° per 69 miles” confusion

The claim

“A globe curves 1° every 69 miles, so long flights and sightlines should visibly tilt — they don’t.”

What is measured

1° ≈ 69 mi (111 km) is just 40,075 km ÷ 360. That is how a degree is defined on the globe, not a problem for it. It is the same ratio Eratosthenes used.

What would show this is wrong

degrees of longitude that do not shrink toward the poles (meridians staying parallel), or a still-water surface that measurably tilts where “level” says it shouldn’t.

Sources

  1. World Geodetic System 1984 (WGS 84). NGA Standardization Document, defining ellipsoid parameters (a, f, b). National Geospatial-Intelligence Agency. WGS 84 link
  2. Length of a degree of latitude and longitude. Arc length per degree from circumference ÷ 360; longitude spacing scales as cos(latitude). WGS 84 / NGA. length of a degree link
  3. The nautical mile — one minute of arc of latitude. Historic definition giving 60 nmi per degree ≈ 69 statute miles. NOAA / BIPM. NOAA: nautical mile link
  4. The length of a degree of latitude. Because Earth is oblate, the length of one degree of latitude increases from roughly 110.6 km near the equator to about 111.7 km near the poles; the Frenc link
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