Ancient astronomers looked at movements in the sun, moon, and stars to guide travelers and keep track of the seasons. Nicholas Copernicus was the first to challenge people"s beliefs that Earth was the center of the solar system and is known as the founder of astronomy. Galileo Galilei built a telescope and spotted craters on the moon and sunspots on the sun. Isaac Newton invented the reflecting telescope and discovered the law of gravity. Astronomers continue to work every day to uncover the mysteries of the universe.