Galileo's Discoveries Using Telescopes, 1609-10
Credited As the First to Make the Spyglass Essential in Astronomy
Jul 1, 2009
Well before Galileo was born in Pisa, Italy, humans had observed and studied the stars and the planets with the naked eye. But with the invention of the telescope early in the seventeenth century, the universe was brought closer to earth. New knowledge of the wide expanse of which the earth is a part would come abundantly to those who had an open mind.
Galileo Makes His First Telescope and Observes the Moon
After hearing that a German-born eyeglass maker living in the Netherlands had invented the telescope, Galileo decided to build one. Originally called a spyglass, Galileo built his first telescope about June or July 1609. His instrument magnified objects by a power of three. He worked on improving it and by August he had made one that magnified objects by a power of eight. And by late 1609, his telescope magnified objects by a power of about 20.
From late November to mid-December 1609, he turned his new aid to the moon. He noted that its surface was not smooth as was widely believed, but rough with craters and mountains. He also observed the phases of the moon from crescent to full and sketched them. Through the telescope he also saw many more stars in the universe than humans believed possible.
Observes Jupiter and Some of Its Moons
Galileo was professor of mathematics at the University of Padua, Italy's most prestigious university, from December 1592 to August 1610. This is where he first used the telescopes he had been building since 1609. In January 1610 he observed four of the 12 moons or satellites that today astronomers know circle the planet Jupiter. Galileo made drawings of Jupiter and the positions of the moons he sighted.
One argument made by those who believed that the planets revolved around the earth and not the sun was this: since the moon was the earth's satellite and revolved around it, if the earth revolved around the sun, it would leave the moon unattended. But Galileo observed that the moons of Jupiter never left their orbit. Galileo reasoned that just because a planet had a moon(s) revolving about it, it did not follow that the planet was the center of a celestial system. In fact there were indications that the earth was a mere planet and not the center of the planetary system. .
Publishes His Early Findings in Sidereus Nuncius
In March 1610 Galileo published his early telescopic findings about the moon, Jupiter and some of the new stars he had seen. He said that the Milky Way was not a clump of unknown matter but a collection of seemingly endless stars. His book of fewer than 60 pages was published in Latin, the language of scholars. Titled Sidereus Nuncius (abbreviated title), the English translation of the book's name has been given as the Starry Messenger, the Sidereal Messenger and other names. Printed in Venice, the 550 copies were sold within a week. Galileo became famous in Europe.
Shortly after its invention, the telescope was used by ship's captains in navigation and by French noblemen to gaze at women riding in carriages. Galileo made the telescope an essential tool for serious astronomers. His most influential astronomical discovery came when he turned his instrument to the planet Venus.
Sources:
Land, Barbara. The Telescope Makers: From Galileo to the Space Age. New York: Thomas Y. Crowell. 1968.
Specifics About Galileo's Telescope
MacLachlan, James. Galileo Galilei: First Physicist. New York. Oxford University Press. 1997. Owen Gingerich, General Editor. Oxford Portraits in Science.
The Meaning of Galileo's Astronomical Discoveries
Further Reading:Galileo, Venus and the Sun-Centered Theory
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