50 Chapter 1
From the Geocentric Theory to the Heliocentric
Theory
The mysterious behavior of planets puzzled people for a long time, as evi-
denced by the fact that etymologically, the word planet comes from the Greek
word for wandering star. People thought that the planets wandered around
and changed their locations, while the other stars—that is, the so-called fixed
stars*—revolved while maintaining the same positional relationships on the
celestial sphere.
Oh yeah, I heard
that explanation
at the planetar-
ium once.
Yeah, I bet the name planetarium
comes from the word planet.
You sure know
a lot of things,
don’t you?
That’s because I went to
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