it was easy Pluto the planet that was named a "Dwarf Planet" because of it's size details he saw that there was some moons which nobody knew about.
optical
Some of Galileo's most significant work was in the field of kinematics, identifying that the total ...by him (or to be written by him) were forbidden, though this latter part was not enforced. ... Galileo Galilei - major areas of study ...
How many years after Luther’s criticism did Galileo begin to study planets?
Galileo experimented with gravity. Newton merely explained how it works, and showed that if his formula is correct, then that explains why the planets move the way they actually do. He may never have needed to experiment.
Philosophy
Jupiter
The first astronomer to study the planet Jupiter with a telescope was none other than Galileo.
Galileo.
Galileo.
Venus is one of the planets that is visible without a telescope. The planet has been known since antiquity. Galileo was the first astronomer to study Venus through a telescope.
1987
optical
Galileo was the first person to use a telescope for technological uses.
Galileo was probably the first to study Jupiter in detail, with his telescope.
Galileo gailes
Galileo gailes
Jupiter. And its moons Europa and Io. Also inspected asteroids Gaspra, Ida, and Dactyl