Galilei, Galileo

Contents

Many books and plays exist on the life of Galilei, the Italian scholar who laid the foundation to the discipline known for many years as "natural philosophy," now called physics.

He was the first to observe the planets through a telescope, and what he saw convinced him that Copernicus was right. How his agressive defense of the Copernican theory turned the Catholic church against him and cost him his freedom is a fascinating story, but it goes beyond our scope here.

Galileo did not invent the telescope; that was done by lensmakers in Holland and elsewhere (eyeglasses had been in use for centuries). Unlike later astronomical telescopes, which turn the picture upside down, the first version worked the way opera glasses do, combining two lenses of different types. Opera glasses magnify about 2-3 times: Galileo pushed the technology to its limits, magnifying his view 8-fold and in a later instrument 33 times.

That was the instrument with which, in 1609-10, Galileo made his revolutionary discoveries. He observed the Moon and saw a world with mountains and "seas," and risking blindness (since the Sun should never be looked at through a telescope) he also observed sunspots. When he turned his telescope to the planet Jupiter, he saw four moons orbiting around it, all practically in the same plane, close to the ecliptic (and therefore, they and the planet all seem to lie on the same straight line; you can get the same view through good binoculars or any telescope), very much like a miniature version of the kind of solar system proposed by Copernicus.

And when he looked at Venus, he saw its visible shape changing like that of the moon, becoming a crescent when Venus was between us and the Sun, a time when most of its sunlit half faced away from Earth. Galileo was persecuted for advocating the world view of Copernicus, but his observations, which were soon confirmed by other astronomers, convinced all scholars that this was indeed the way the Sun, Earth, Moon and the planets were related.

Related EoC Articles

• Resource: The Galileo Project

External Links

• Galileo: The Man and His Science - A Resource Guide to Materials in English, from International Year of Astronomy 2009. (PDF)
• Galileo and the Sinful Spyglass - from Man, Moment, Machine by History.com

Further Reading

• "Galileo and the Scientific Revolution" by Laura Fermi and Gilberto Bernadini, Basic Books, 1962.
• "The History and Practice of Ancient Astronomy" by James Evans, Oxford Univ. Press, 1998; Reviewed by J.D. North, "Nature ", vol. 398, p. 385, 1 April 1999.

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