astronomy: Brahe and Kepler

The great astronomer Tycho Brahe (1546–1601) was principally an observer; a conservative in matters of theory, he rejected the notion that the earth moves. Under the patronage of King Frederick II, Tycho established Uraniborg, a superb observatory on the Danish island of Hveen. Over a period of 20 years (1576–97), he and his assistants compiled the most accurate and complete astronomical observations to that time. At his death his records passed to Johannes Kepler (1571–1630), who had been his last assistant. Kepler spent nearly a decade trying to fit Tycho's observations, particularly of Mars, into an improved system of heliocentric circular motion. At last, he conceived the idea that the orbit of Mars was an ellipse with the sun at one focus. This led him to the three laws of planetary motion that bear his name (see Kepler's laws).

Sections in this article:

• Introduction
• Modern Techniques, Discoveries, and Theories
• Astrophysical Discoveries
• Galileo's Telescope
• Brahe and Kepler
• The Copernican Revolution
• The Alexandrian School and the Ptolemaic System
• Greek Innovations
• Ancient Astronomy
• Bibliography

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