In 1608, Galileo Galilei is credited as the first to turn his telescope to the heavens.
He soon discovered craters on our Moon, sun spots, the moons of Jupiter, and that Venus has phases like our Moon.
Galileo claimed that his observations only made sense if all the planets revolved around the Sun (as proposed by Aristarchus and Copernicus) rather than the Earth.
Galileo Galilei
1564 - 1642
Historical Background of Spectroscopy
The Inquisition eventually forced Galileo
to publicly recant this conclusion.