The History of Astronomy Part 6 The Debate Heats Up Tycho and Kepler

Tycho Brahe (1546-1601) Tycho Brahe was a Danish Astronomer He made the most accurate observations ever made without the aide of a telescope. He also: Corrected Standard Astronomical Tables Studied a Supernova in Cassiopeia (1572) and determined that it must be far beyond the supposed “spheres” of the planets and stars That is: Stars are at different distances. Proposed his own Model of the Universe

Tycho Brahe’s Model Tycho rejected Copernicus for the old reason: Where’s the Parallax? So Tycho left the Earth Stationary and had the Moon & Sun Orbiting it. But he had all the other planets orbiting the Sun! With Venus and Mercury closer to the sun than Earth.

Johannes Kepler (1571-1630) Kepler was a supporter of the Copernican model of the Universe He … wrote a treatise (1596) in support suggested the Sun emitted a force that pulled on the planets. In 1600 he became Tycho Brahe’s assistant and took over when he mysteriously died in 1601 used Tycho Brahe’s data to chart Mars’ motion and showed that it and Earth both orbit the Sun… … but in ellipses!

Kepler’s Laws Kepler’s improved Copernican model had orbits that obey three laws: The Planets orbit in ellipses with the sun at one focus. The speed of the planet varies so that a line joining the sun and Planet will sweep out an equal area in an equal time. That is when closer faster and farther slower. 3. The period of revolution is related to the length of the semimajor axis by: P² = a³