Galileo and His Four Findings

Today we reviewed the the four most important things that Galileo discovered.

The Moon

In 1609, scientists believed that the moon was a perfect, smooth sphere (think of the Greek who believed that the planets were perfect, crystal balls.) Galileo did NOT think like this.

On November 30th, 1609, he trained his telescope to the moon for the first time. His discoveries changed how scientists viewed the moon... He observed that the moon in fact is not a perfect sphere, that it is actually is home to many craters, mountains and other features much like those of earth. He concluded that the dark lines he saw were shadows... and that these shadows were results of the not so perfect lunar surface.

He also discovered the phases of the moon after observing it for a period over several months.

Jupiter

One of the brightest body's that we can see with the naked human eye is Jupiter. No one is aware of when Jupiter was discovered, but it has been known of wayyyy long before Galileo showed up.

Galileo trained his telescope on Jupiter on January 7th, 1610. Through observations, he noticed three fixed "stars" near the body of Jupiter. They were brighter than the others, but he didn't think much of it at first. The next night, the "stars" had appeared to shift closer to each other... fast-forward to January 15th and one of the "stars" disappeared behind Jupiter. It was on this night that Galileo concluded that these "stars" were not in fact stars at all, but moons orbiting the planet Jupiter. These four moons today are known as the Galilean Moons.

Venus

Following Galileo's discoveries of the moon in 1609 and Jupiter in January of 1610, he decided to study and observe the planet Venus. His observations started in the late fall of 1610 and continued on for several months. He noticed that Venus went through a series of phases similar to our moon... from a small circular disk to various phases of crescent.

Sunspots

Galileo and Thomas Harriot started observations of Sunspots in late 1610, though they did not mean much to him. However, it was Christoph Scheiner's work on Sunspots in March of 1611 that encouraged Galileo to write his own letters on sun-spots. Scheiner published three letters on solar sunspots which he submitted to Marc Wesler in January 1612, where he stated that sunspots were satellites of the sun... this supported the well known and accepted theory of an unchanging universe. Wesler however, was interested in Galileo's opinion on the matter.

Galileo resumed his work on sunspots in April 1612, and later published letters to Wesler in 1613. He identified sunspots as markings on the sun... which we now know as correct!

Galileo's Conclusion

His work on these four topics left Galileo to conclude that the sun was the center of the solar system... The Moon's phases were evidence that yes the moon does orbit around the earth, but the imperfectness of its surface contradicted Aristotle's idea of perfect spherical "heavenly bodies". Galileo's observations of Jupiter showed that bodies could orbit around other objects other than Earth. Also, if Earth was the center of the solar system than the phases of Venus that Galileo observed would have never been visible... and finally, in order to see the sun-pots on the surface of the Sun disappearing and reappearing, the Earth would HAVE to be orbiting around the Sun... Making the Sun the center of the solar system.