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Kepler's Planets
Among his many discoveries, Johannes Kepler (1571-1630) was the first to describe planetary motion through three basic laws: 1) Planets move in an elliptical orbit with the sun at one focus, 2) Every planet passes the same amount of area in the same amount of time, 3) The square of the period of a planet is proportional to the cube of its average distance from the sun. Kepler was the inspiration and the namesake for a new NASA mission to discover planetary systems besides our own solar system.
The role of the Kepler Mission is to survey our galaxy and, over the course of about three and a half years, detect exoplanets, or planets that are similar in nature to Earth. These kinds of terrestrial planets can be found in regions which potentially support life, called habitable zones. Kepler consists of a telescopic photometer that will search an area of 105 square degrees (about the size of a hand held at arm's length). Using the transit method, Kepler will observe over 100,000 stars, hunting for exoplanets.
The transit method involves watching for a small decrease in the brightness of a star. This indicates that a planet passed in front of, or transited, the star--just like when we occasionally observe Mercury or Venus as a black dot passing in front of the sun. When scientists find an exoplanet, they can determine its orbital size based on the period and they can use Kepler's Third Law of planetary motion to calculate the star's mass. They can also use the star's temperature and the planet's orbital size to approximate the planet's temperature and determine if it could be habitable.
Kepler launched on March 6, 2009, at 10:49 p.m. EST.
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