The picture below can help us determine the formula for the diameter of the parallel at latitude t. It is the figure from the preceding page with one addition. We have filled in the green triangle -- the hypotenuse of this triangle is one radius of the earth. The top edge of this triangle is the radius of the parallel at latitude t. In this picture t is 40 degrees North. The angle between these two sides is t.
Radius of Parallel Adjacent Side -------------------- = --------------- Radius of Earth Hypotenuse
is the ratio between the adjacent side and the hypotenuse of a right triangle
with angle t. This ratio has a name -- cos t and is easily
computed. In fact, even $10.00 calculators have a key to compute the cosine.
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Department of Mathematics, Engineering, Computer Science, and Physics
Carroll College, 1601 N. Benton Avenue, Helena, MT 59625
This work is copyrighted c 1996 by Carroll College, Helena, MT 59625.