MadSci Network: Astronomy

Re: How high would one have to be to see the curve of the Earth?

Date: Thu Mar 7 11:29:06 2002
Posted By: Kisha Delain, Staff, Chandra Mission Planning, Harvard-Smithsonian Center for Astrophysics
Area of science: Astronomy
ID: 1012162178.As

The difficulty with Earth is that there is topography - for the Rocky
Mountains you would have to be higher than over the ocean.  With no
atmosphere, it would be possible to see your horizon deviate from a
straight line fairly easily as long as there is nothing in the way (such as
a mountain, or an ocean wave) no matter what height you are at.

However, seeing your horizon curve doesn't give you a sense as to whether
or not you are in fact standing on a sphere.  You could be at the center of
a disk, which would also look as though your horizon curved.  

There are ways to test, of course, that this is not the case - an obvious
one would be to go to a stationary point above the earth (if you can find
one!) and watch it rotate around one complete rotation.  If you are on a
spherical planet instead of a disk, the horizon you see should remain the
same size through the whole rotation.  If you were on a disk, it would
instead decrease as an oval to a straight line, and then increase as an
oval again to a round circle.

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