Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

September 13, 1997
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Kepler Discovers How Planets Move
Credit: Johnnes Kepler Gesammelte Werke , C. H. Beck, 1937

Explanation: Johannes Kepler used simple mathematics to describe how planets move. Kepler was an assistant to the most accurate astronomical observer of the time, Tycho Brahe. Kepler was able to use Brahe's data to show that planets move in ellipses around the Sun (Kepler's First Law), that planets move proportionally faster in their orbits when they are nearer the Sun (Kepler's Second Law), and that more distant planets take proportionally longer to orbit the Sun (Kepler's Third Law). Kepler lived from 1571 to 1630, during the time of discovery of the telescope. Kepler was one of the few vocal supporters of Galileo's discoveries and the Copernican system of planets orbiting the Sun instead of the Earth.

Tomorrow's picture: MyCn18: An Hourglass Nebula

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.