The Manga Guide to the Universe

66 Chapter 1 Is Earth the Center ofthe Universe?

What Is the Approximate Distance to the Horizon?

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

rh h

=+

()

−

=+

2

2

2

2

Since the radius of Earth ( ...