CALCULATION OF THE SIZE OF THE EARTH

by Knut Jørgen Røed Ødegaard

You have now measured the altitude of the Sun. Before continuing you or your teacher must exchange measurements with the cooperating school.

Now you are going to calculate the size of the Earth!

1. Use a map and measure the distance between the latitudes of your school and the other school. If, for instance, one of them is situated at 67 degrees north, and the other one at 60 degrees north, you must measure the distance between these latitudes in purely north-south direction. You must therefore pretend that the schools are at the same degree of longitude.

   We should have measured this distance by hiking or driving, but that would take too much time!

2. Calculate the difference in altitude of the Sun:
   Difference = altitude of Sun at southern school - altitude of Sun at northern school

Measurements of the altitude of the Sun from two different locations tell us how much of the 360 degrees of the circle that is lying between the locations. Illustration: astronomy.no

3. Finally: The circumference of the Earth!
   Let us denote the distance between the latitudes of the schools measured in kilometers Y. Let us denote the difference in solar altitude X.

   Circumference of Earth = Y * (360/X) kilometers

   Diameter = Circumference/Pi or approximately circumference/3

Amazing - isn't it - that we can calculate the size of the whole Earth just by measuring the solar altitute on two different locations?

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