What are the circumferenceS (plural) of the earth?

Question

I need to know the circumference at the 30th parallel, the 40th, etc. Does anyone know of a chart or a way to estimate it?

Answer 1

You can approximate them with a little applied geometry.

The radius from a vertical from pole to pole, to the outside of the earth at the desired latitude is what you need to figure it out. This radius is the full Earth radius * cosine of the latitude angle. Then, the circumference at that latitude is 2π times that latitude radius.

For example, at 30 latitude:
radius(30) = ~6400cos30 = ~5540 km
circumference(30) = 2π*5540 = 34800 km (21,600 miles)

Answer 2

Circumference is the longest measurement of a globe shaped object and circles. At the equator, it is approximately 25,000 miles give or take a few miles.

Answer 3

Both of the above answers are correct when you assume the Earth is a perfect sphere. It is not, it bulges around the equator and squats at the poles.

Make sure your professor is looking for a data from a perfect sphere if you use these techniques.