Galileo Galilei

Galileo made a series of profound discoveries using his new telescope, including the moons of the planet Jupiter and the phases of the planet Venus (similar to those of Earth's moon).

 As a professor of astronomy at University of Pisa, Galileo was required to teach the accepted theory of his time that the sun and all the planets revolved around the Earth. Later at University of Padua he was exposed to a new theory, proposed by Nicolaus Copernicus that the Earth and all the other planets revolved around the sun. Galileo's observations with his new telescope convinced him of the truth of Copernicus's sun-centered or heliocentric theory.

These are different phases of the moon he observed.