Kepler2 - eccentricity . The eccentricity of the ellipses...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Kepler's Laws of Planetary Motion Planet orbits have small eccentricities (nearly circular orbits) which is why astronomers before Kepler thought the orbits were exactly circular. This slight error in the orbit shape accumulated into a large error in planet positions after a few hundred years. Only very accurate and precise observations can show the elliptical character of the orbits. Tycho's observations, therefore, played a key role in Kepler's discovery and is an example of a fundamental breakthrough in our understanding of the universe being possible only from greatly improved observations of the universe. Most comet orbits have large eccentricities (some are so eccentric that the aphelion is around 100,000 AU while the perihelion is less than 1 AU!). The figure above illustrates how the shape of an ellipse depends on the semi-major axis and the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: eccentricity . The eccentricity of the ellipses increases from top left to bottom left in a counter-clockwise direction in the figure but the semi-major axis remains the same. Notice where the Sun is for each of the orbits. As the eccentricity increases, the Sun's position is closer to one side of the elliptical orbit, but the semi-major axis remains the same. To account for the planets' motion (particularly Mars') among the stars, Kepler found that the planets must move around the Sun at a variable speed. When the planet is close to perihelion, it moves quickly; when it is close to aphelion, it moves slowly. This was another break with the Pythagorean paradigm of uniform motion! Kepler discovered another rule of planet orbits: a line between the planet and the Sun sweeps out equal areas in equal times. This is now known as Kepler's 2nd law ....
View Full Document

This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

Page1 / 2

Kepler2 - eccentricity . The eccentricity of the ellipses...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online