116 Chapter 2 From the Solar System to the Milky Way
The Universe Is Steadily Getting Larger
Whether they believed in the geocentric theory or the heliocentric theory, people in the
16th century thought the universe consisted only of Earth, the Moon, the Sun, planets of
the solar system, and many other stars. The only things moving independently in the sky
were the planets—people thought the other stars were just affixed to the celestial sphere
like lanterns hanging from a wall in the background, forming various constellations.
However, Galileo Galilei felt there were problems with that view of the universe. He
used a telescope he had built ...
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