Chapter 2-Universe as we know it

# Chapter 2-Universe as we know it - 2.1 The Laws of...

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2.1 The Laws of planetary Motion Tycho Brahe’s Observations and Johannes Kepler The Orbit of Mars Initially Kepler began his analysis under the assumption that the orbits of planets were circles, but realized that the observations contradicted this idea. Eventually he discovered that the orbit of Mars had the shape of a somewhat flattened circle, or ellipse .

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What is an Ellipse? In an ellipse, the sum of the distances from two special points inside the ellipse to any point on the ellipse is always the same.
The two points inside the ellipse are called its foci (singular: focus ). The widest diameter of the ellipse is called its major axis . Semimajor axis - the distance from the center of the ellipse to one end, half of the major axis. The shape (roundness) of an ellipse depends on how close together the two foci are, compared with the major axis. The ratio of the distance between the foci to the length of the major axis is called the eccentricity of the ellipse.

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Laws of Planetary Motion Kepler generalized his observations of the elliptical motion of Mars in his first law and said that the orbits of all the planets are ellipses.
1. Kepler's First Law Each planet moves about the Sun in an orbit that is

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## This note was uploaded on 09/12/2011 for the course RELIGION 101 taught by Professor Staff during the Fall '10 term at Temple.

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Chapter 2-Universe as we know it - 2.1 The Laws of...

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