Earth's Atmospheric Thickness at Tangent
If I am standing on the Equator, and a star is rising on the
eastern horizon, how much atmosphere would I be looking through?
A lot! I remember when we were observing, when the telescope was
close to the horizon it would tell us that we were looking through 8
times the amount of air as when we look overhead. So the answer is at least 8.
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Update: June 2012