Galileo's observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model.
Galileo saw the four largest moons of Jupiter in orbit around the planet, proving that the Ptolemaic system was not simpler - the solar system was not geocentric (the planets and the sun did not orbit around the earth).
As far as the observations of Venus go, Galileo saw that Venus displayed phases very much like our moon. Now, according to the Ptolemaic system, Venus could only display a crescent phase because its epicycle put it always in between Earth and the sun. The Copernican system put everything rotating around the sun, and in this way it explained the phases of Venus.
Think of it this way, if Venus is always in between the sun and the earth, how can we ever see it completely lit up, like a full moon? The sun is always on the other side of it, so Venus must at some point go on the other side of the sun.
Galileo and Copernicus were two of the scientists to disprove Ptolemy's geocentric theory of the universe. The Ptolemaic theory stated that the center was earth.
Ptolemy proposed a geocentric model, with Earth at the center and planets orbiting it. Copernicus suggested a heliocentric model, with the Sun at the center of the solar system. Galileo's telescopic observations supported the heliocentric model and provided evidence for Copernicus' theory.
Galileo had a theory, it was that the earth was NOT in the centre of the solar system like everyone thought, he made the first telescope and proved everyone wrong by looking into space and seeing that the sun was in the centre of the solar system, not the earth, doing this he also invented the telescope.
Galileo did not have his own theory. He was a supporter of Copernicus's heliocentric theory and an opponent of the geocentric Ptolemaic theory. Eventually both theories were rejected in favour of Kepler's theory. But Kepler's theory uses the heliocentric idea from Copernicus's theory.
None of it but Galileo's discoveries with the telescope were very important in raising questions about the old Ptolemaic theory, which was geocentric. However Galileo's discovery of Venus's phases was not a proof of the heliocentric principle because Tycho produced a geocentric model that explained Venus's phases.
Galileo and Copernicus were two of the scientists to disprove Ptolemy's geocentric theory of the universe. The Ptolemaic theory stated that the center was earth.
Galileo Galilei
As proposed by the Heliocentric Theory, the Sun is the center of the Solar System.
Galileo discovered two important things: the moons of Jupiter and the phases of venus. Both discoveries raised doubts about the old Ptolemaic system which was geocentric, and the phases of Venus showed that it was definitely wrong. But neither discovery proved that Copernicus's theory - supported by Galileo - was right. This is because Tycho's geocentric system explained the phases of Venus satisfactorily.
Ptolemy proposed a geocentric model, with Earth at the center and planets orbiting it. Copernicus suggested a heliocentric model, with the Sun at the center of the solar system. Galileo's telescopic observations supported the heliocentric model and provided evidence for Copernicus' theory.
ptolemaic
Galileo had a theory, it was that the earth was NOT in the centre of the solar system like everyone thought, he made the first telescope and proved everyone wrong by looking into space and seeing that the sun was in the centre of the solar system, not the earth, doing this he also invented the telescope.
Galileo did not have his own theory. He was a supporter of Copernicus's heliocentric theory and an opponent of the geocentric Ptolemaic theory. Eventually both theories were rejected in favour of Kepler's theory. But Kepler's theory uses the heliocentric idea from Copernicus's theory.
None of it but Galileo's discoveries with the telescope were very important in raising questions about the old Ptolemaic theory, which was geocentric. However Galileo's discovery of Venus's phases was not a proof of the heliocentric principle because Tycho produced a geocentric model that explained Venus's phases.
ptolemy formulated the geocentric theory...
geocentric theory invented by phtolemy
Heliocentric = The Sun is at the center of our solar system. Geocentric = The Earth is at the center of our solar system. Insisting the Sun is at the center, which it is, once very much angered the church.