Galileo's Research and Discoveries with the Telescope
Galileo first used his 20 magnification telescope to look at the night sky in October of 1609. The first thing he examined was the moon. He discovered that the surface was irregular and earth-like, with chains of mountains and deep valleys. This went against the belief that all heavenly objects were perfect and unblemished. He sketched what he saw and the drawings were later published in The Starry Messenger.
“I have been led to the opinion and conviction that the surface of the moon is not smooth, uniform, and precisely spherical as a great number of philosophers believe it (and the other heavenly bodies) to be, but is uneven, rough, and full of cavities and prominences, being not unlike the face of the earth, relieved by chains of mountains and deep valleys.”
(Galileo Galilei, The Starry Messenger) |
On January 7, 1610 Galileo spotted three little stars near Jupiter that had never been seen before. The stars were in a straight line to the east of Jupiter. Galileo assumed that they were normal stars, but the formation interested him and he returned to it the next night. His expectation was that Jupiter would have moved west and would have left the three little stars behind. But instead he found that they had moved to the west of Jupiter. This fascinated him and he returned to the formation each night. Galileo discovered three things about the stars. First, they never left Jupiter and appeared to be carried along with the planet. Second, there were not three, but four stars. Third, they changed positions each night in respect to the other stars and Jupiter. By the 15 of January he had figured out that they were four moons of Jupiter. They were later named Io, Europa, Ganymede and Calisto. |
Galileo’s third discovery was the phases of Venus. To the naked eye, Venus always appeared to be a circular spot of light, but through Galileo’s telescope it appeared to have phases like the moon. Galileo realized that these phases would only happen if Venus rotated around the Sun, not the Earth. This was not his most famous discovery, but it was his most important. The discovery of Venus’s phases gave Galileo solid proof and a reason to believe in the Copernican system.
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