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Name: Charles
Status: Other
Age: 50s
Location: N/A
Country: N/A
Date: N/A 

How can I calculate the circumference of the Earth at different latitudes? Example: What would the distance around the Earth be at 30 degrees latitude?

As you go from 0 degrees latitude (the equator) to 90 degrees (north or south poles), the circumference of the circle defined by that latitude line will decrease in direct proportion to the cosine of the angle of latitude. Thus, the circumference of the circle is

C = 2 pi r cos(x),

where pi = 3.14159..., r = the earth's equatorial radius = 6378 km, and x is the angle of latitude.

This formula is not entirely correct, as it assumes the earth is a perfect sphere, which it isn't. In fact, the earth bulges out a bit at the equator, as a consequence of its rotation. This effect is small, however, and the formula is accurate to within one percent.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

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