The Italian astronomer and physicist Galileo is often credited for inventing the telescope. In truth, a Dutch optician invented the telescope before 1609, but as soon as Galileo learned about this important new instrument, he set about making one of his own.
Galileo worked to improve his telescope and turned it on the sky. In a matter of months he made some astonishing discoveries, including mountains and valleys on the moon, the phases of Venus, and the four big moons orbiting Jupiter. These observations supported the Copernican view of the solar system. Galileo also used the telescope to discover that the Milky Way is composed of countless stars too faint to be seen with the unaided eye.
Galileo’s popular advocacy of the Copernican system provoked the opposition of the Roman Catholic Church, and he was accused of being a heretic. In 1633 he was forced to denounce the Copernican system and was sentenced to house arrest for the rest of his life.