However, astronomy took another great leap when Galileo Galilei (1564-1642), who also believed the theory of Copernicus, pointed his telescope, a new invention from Holland, at the sky. Among many other celestial features, he discovered craters and mountains on the moon, four satellites orbit the planet Jupiter and rings of planet Saturn. The use of telescopes open up a new chapter on astronomy and have become indispensible tools for astronomers to study celestial objects in great details.
1.-Copernicus changed the way of thinking, not only astronomically but also religiously. This was because the Catholic teachings were based on the theory.
Kepler create the three laws of planetary:
1. The orbit of every planet is an ellipse with the sun at a focus.
2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
5.-in 1929, Edwin Hubble demonstrated that the universe was expanding, (considered by many as one of the most important cosmological discoveries ever made), and formulated what is now known as Hubble's Law to show that the other galaxies are moving away from the Milky Way at a speed directly proportionate to their distance from it.