AstroGlossary - K
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Kelvin
A unit of temperature equal in magnitude to Celsius (1 K = 1 degree C) and abbreviated with K. Zero degrees Celsius, the freezing point of water, equals 273.15 K. Absolute Zero is defined as 0 K. The surface of the Sun is about 6000 K, while nuclear fusion reactions deep in the center of the Sun raise the temperature to about 15 million K. Kepler's Laws
Kepler summarized planetary motion with three rules, or laws. Kepler's First Law, the Law of Ellipses: A planetary orbit is an ellipse with the Sun at one focus. Kepler's Second Law, the Law of Equal Areas: As a planet orbits the Sun, it sweeps out equal areas of the ellipse in equal times. This behavior means that the planet's orbital velocity varies with distance from the Sun. At perihelion, the planet is at maximum speed and at aphelion the planet crawls along at minimum speed. Kepler's Third Law, the Harmonic Law: Even though the orbital velocity of a planet changes constantly, one relationship does remain constant. The orbital period is directly related to the average distance between the planet and the Sun. This law implies that planetary orbital velocity decreases with increasing distance from the Sun. For instance, the orbital velocity of Mercury (47.9 km/s) is far greater than Pluto (4.7 km/s). See also: Kepler, JohannesKepler, Johannes
A German mathematician and astronomer who lived from 1571 - 1630. Kepler was the first person to model planetary orbits as ellipses instead of circles. He tested his theory of elliptical orbits using Danish astronomer Tycho Brahe's observations of planetary motion in the sky. In 1609, he published his findings in a book called Astronomia nova or The New Astronomy, where he summarized planetary motion with three rules, or laws. See also: ellipse, Kepler's LawsKuiper Belt
A ring of small, icy objects that surrounds the solar system beyond the orbit of Neptune. Postulated by American astronomer Gerard P. Kuiper in 1952, it may be the birthplace of comets whose periods are less than 200 years, such as Halley's Comet.
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