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Explore the clash between Brahe's geocentric model and Kepler's heliocentric system. Learn how Kepler's laws transformed our understanding of planetary motion in this captivating historical account.
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The History of Astronomy Part 4 The Debate Heats Up: Brache and Kepler
Copernicus's “Simple Heliocentric Model” caused a great stir in intellectual circles of Europe. • At first it met opposition and even ridicule from such great astronomers as Tycho Brahe. But some agreed and went further with even more “ridiculous” proposals…
Both the Engish astronomer Thomas Diggs and Italian frair/mathematician Giordano Bruno went further than Copernicus, by proposing that the universe is infinite, containing infinitely many stars.
Tycho Brahe (1546-1601) • Tycho Brahe was a Danish aristocrat whose patrons included King Frederick II of Denmark and Rudolf II, Holy Roman Emporer. • He recorded the most accurate observations ever made (including today) without the aid 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. THEREFORE: Stars are at different distances.
Tycho Brahe’s Model • Tycho rejected Copernicus’s heliocentric system for the same old reason: • Where’s the Parallax? So… • Tycho left the Earth stationary with the Moon & Sun orbiting it. • But then he had all the other planets orbiting the Sun, with Venus and Mercury closer to the sun than Earth.
Johannes Kepler (1571-1630) • Johannes Kepler, a German mathema-tician and astro-nomer, was a supporter of the Copernican model of the Universe. • Kepler was also the first scientist to combine astronomy and physics.
Kepler: • wrote a treatise (1596) in support of the heliocentric system. • suggested the Sun emitted a force that pulled on the planets. x
…became Tycho Brahe’s assistant and took over when Brache mysteriously died in 1601.
Used Brahe’s data to chart Mars’ motion and showed that both it and Earth 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.
Law #2: 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…faster when closer, and slower when farther away.
The 3rd Law of Planetary Motion • The square of a planet's orbital period is proportional to the cube of the semimajor axis of the orbit. • Expressed Mathematically: P2=a3 • where P is the planet's orbital period measured in years, and a is the semimajor axis of the planet's orbit measured in AUs.