stars. They called these bright spots in the skyplanets, which in Greek means “wanderers.”
Today we know that the planets are not stars, but members of our solar system that orbit
the Sun. The Greeks also identified constellations, patterns of stars in the sky. They
associated the constellations with stories and myths from their culture. Constellations still
help astronomers today; they are used to identify different regions of the night sky.
Galileo’s Observations
Ancient astronomers knew a lot about the patterns of stars and the movement of objects in
the sky, but they did not know much about what these objects actually were. All of that
changed in the year 1610, when Galileo turned a telescope toward the heavens. Using a
telescope, Galileo made the following discoveries (among others):
- There are more stars in the night sky than the naked eye can see.
- The band of stars called the Milky Way, consists of many stars.
- The Moon has craters (SeeFigure23.13).
- Venus has phases like the Moon.
- Jupiter has moons orbiting around it.
- There are dark spots that move across the surface of the Sun.
Figure 23.13: Galileo was the first person known to look at the Moon through a telescope.
Galileo made the drawing on the left in 1610. The image on the right is a modern photograph
of the Moon. ( 24 )
Galileo’s observations challenged people to think in new ways about the universe and Earth’s
place in it. About 100 years before Galileo, Nicolaus Copernicus had proposed a controver-