Astronomical Discoveries
"The diversity of the phenomena of nature is so great, and the treasures hidden in the heavens so rich, precisely in the order that the human mind shall never be lacking in fresh nourishment." - Johannes Kepler
MC Dvorak String Quartet 12 in F Fourth Movement
Galileo first observed the moon in November 1609. By this time Galileo had improved the magnification to twenty times. It was the Church’s belief that heavenly bodies had smooth and perfect surfaces. However, Galileo was able to see that the moon’s surface was not smooth, as believed, but had mountains and valleys. In a letter Galileo wrote:
. . . it is seen that the Moon is most evidently not all of an even, smooth, and
regular surface, as a great many people believe of it and of the other
heavenly bodies, but on the contrary it is rough and unequal. In short it is
shown to be such that sane reasoning cannot conclude otherwise than that
it is full of prominences and cavities similar, but much larger, to the
mountains and valleys spread over the Earth's surface. (Sidereus Nuncius,
11)
Galileo’s next discovery was of Jupiter’s moons. The first night he saw three of them, one to the west of Jupiter and two to the east. The next night Galileo found they were to the west of Jupiter. Days later Galileo was able to see all four satellites. Galileo concluded that they were moons orbiting Jupiter. According to geocentrism, the earth wasn’t a planet because it had a moon, yet here was Jupiter with four. This made Galileo believe that the earth was a planet, and since in Copernicus’ model the earth was just another planet revolving around the sun, Galileo also thought that this was proof of a heliocentric universe.
Galileo's observations of the moon (above) and Jupiter's satellites (below)
This idea was not acceptable to the Church who believed in geocentrism. It could still be said that the moons orbited Jupiter while it orbited the earth, “yet the discovery of heavenly bodies that revolved around another planet and not around the Earth had shaken the pillars of the old cosmology.” (Stefoff, 26)
Galileo’s third discovery was of Venus’ phases. According to the geocentric theory, Venus would always be seen in crescent, or at most, half phase because it remains between the sun and the earth. Yet when Galileo observed Venus he was able to see Venus in its full phase.
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Galileo's Battle for the Heavens, PBS
This, Galileo thought, finally proved geocentrism was wrong. However, the Church was still skeptical about accepting Copernicanism. This was such a new concept; it would take some time to accept. As Christopher Scheiner stated in 400 Years of the Telescope, “It’s easy from where we stand, in the 21st century, to look back and say these people were wrong. Yes, but they weren’t dumb. They just had to grow an understanding of this new science.” Although Galileo’s discoveries did not fit with the geocentric theory, the Church still held on to the idea that the Earth was the center of the universe.
Galileo’s last observation was of sunspots. Like the moon, the sun was believed to be perfect, but Galileo could see that there were spots on the surface. These imperfections provided another argument that heavenly bodies were not made of aether.
When Galileo published his book, Dialogue Concerning Two Chief World Systems, which undoubtedly showed which side he was on in the geocentric versus heliocentric debate, he was charged with heresy by the Church. Found guilty, he had to recant his views and was put under house arrest for the remainder of his life. His works were put on the banned book list.