How We Know The Earth’s Shape (1960)

Describes the history of understanding the shape of the Earth. It mentions that early man thought the earth was flat, but later people noticed that ships seemed to sink below the horizon, which led to the conclusion that the earth was curved. The ancient Greeks used the shape of the shadow during lunar eclipses to further conclude that the earth was round. Later, scientists like Isaac Newton and through observation of satellite orbits, it was determined that the Earth is not a perfect sphere, but rather slightly flattened at the poles and bulging at the equator. The film also mentions the use of radio signals from satellites to measure the Earth’s shape.

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