If Earth was flat and the air was perfectly clear, you could see for an unlimited distance.
Therefore, the fact that there is a horizon—that is, an apparent line that separates Earth
from the sky—is evidence that Earth is round.
So approximately how far is it to the horizon?
If we let r represent the radius of Earth and let h represent the height of the observer’s
viewpoint, then the relationship to the desired distance L will be as follows, according to the
Pythagorean theorem:
rh
rL
+
()
=+
2
22
Therefore,
Lr
hr
rhh
=+
()
−
=+
2
2
2
2
Since the radius of Earth ( ...
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