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!
- 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
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
We should have measured this distance by hiking or driving, but that would
take too much time!
- 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
- 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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Created Dec. 31,03, last updated Dec. 31, 03 by Knut Jørgen Røed Ødegaard