History and Biography of Astronomers: Kepler, Galileo, and Newton

About the history and biography of astronomers Kepler, Galileo, Newton, and Huygens the development of modern astronomy.

The Astronomers

Johannes Kepler (1571-1630) was a strange figure. With a constantly running nose, with more interest in astrology and numerology than astronomy, he may have been the best mathematician of his times. Using Tycho's exquisite data, Kepler was able to determine that Mars--and by extension every planet--travels in an elliptical orbit--not the perfect circles that Copernicus had supposed. Kepler described the motion of the planets, saying that the speed of a planet depends on its distance from the sun--the farther away the slower it moves--without the use of computers or any mathematical aids such as logarithms.

At the same time that Kepler was making his discoveries, in Italy Galileo Galilei (1546-1642) was introducing the telescope into astronomy. Not the inventor, but the 1st user of this instrument in astronomy, Galileo was also the 1st to observe the craters of the moon, to observe that the Milky Way is made up of stars, and to observe that Jupiter has 4 moons orbiting around it. This last impressed Galileo as a miniature solar system and as proof of Copernicus' theory. Adherence to this new concept caused Galileo to get in trouble with the powerful Church. After a number of judicial hearings, he lived his last years under house arrest.

But why do the planets swing around the sun? Why don't they go spinning into space like a yo-yo with a broken string? Isaac Newton (1642-1727) provided the answer. During the plagues of 1665-1666 Newton had to return to his family farm. During this unhurried time Newton was able to discover the true nature of gravity and write laws describing its nature. Along with the development of the reflecting telescope, calculus, and theories on the behavior of light, Newton made considerable contributions to astronomy without discovering any celestial objects.

Christiaan Huygens (1629-1695) was an intellectual rival of Newton. His discoveries included the Orion Nebula in 1656, the markings on Mars, Saturn's moon Titan in 1656, and the shape of the rings of Saturn.

One of the 1st uses of Newton's theory of gravitation was in explaining comets. In the 15th and 16th centuries there had been a large number of bright comets. Comets, traditionally objects of fear, were believed to foretell earthquakes, floods, and the death of kings. Edmund Halley (1656-1742), a colleague and ally of Newton's, used the new law and established the comets of 1682, 1607, and 1531 as being the same comet. Further, he predicted that this comet would reappear in 1758, which it did. It was promptly named Halley's Comet. It last appeared in 1910. Halley was also the 1st to catalog the stars in the southern hemisphere.

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