Oblateness of the Earth

a quantity that characterizes the degree to which the earth is flattened in the direction of its axis of rotation, that is, the deviation of the earth’s shape from that of a sphere. The polar oblateness of the earth α is expressed by the equation

where a is the equatorial radius of the earth and b is the polar radius. According to modern findings, α = 1:298.3. With the discovery that the earth is also flattened at the equator, the concept of the equatorial oblateness of the earth was introduced:

where a₁ and a₂ are the maximum radii of the earth’s equator. According to available data, ∊ = 1:30,000, and the difference between a₁ and a₂ is approximately 210m.