In 1609, Galileo heard about the invention of the spyglass, a device which made distant objects appear closer. Galileo used his mathematics knowledge and technical skills to improve upon the spyglass and build a telescope. Later that same year, he became the first person to look at the Moon through a telescope and make his first astronomy discovery. He found that the Moon was not smooth, but mountainous and pitted - just like the Earth! He subsequently used his newly invented telescope to discover four of the moons circling Jupiter, to study Saturn, to observe the phases of Venus, and to study sunspots on the Sun.
Galileo's observations strengthened his belief in Copernicus' theory that Earth and all other planets revolve around the Sun. Most people in Galileo's time believed that the Earth was the center of the universe and that the Sun and planets revolved around it.
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