Astro Glossary

  • Kepler Mission

    Kepler is a roughly 1-meter-diameter telescope that is staring at 150,000 Sun-like stars in the constellations Cygnus and Lyra. It will watch those stars for about three and a half years continuously, without ever closing its eyes. Kepler will look for events called transits, in which a planet briefly passes in front of its parent star, blocking a little bit of the star’s light.The goal is to find Earth-size planets around Sun-like stars.

  • Kepler, Johannes

    A German mathematician and astronomer who lived from 1571 to 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 (The New Astronomy), in which he summarized planetary motion with three laws.

  • 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).

  • Kuiper Belt

    A wide belt beyond the orbit of Neptune, the most distant planet from the Sun, that is theorized to contain tens of millions of icy bodies. The most famous member of the belt is Pluto, but it also includes three other objects that have been classified as dwarf planets. Most of the Kuiper Belt’s members are leftover “building blocks” from the birth of the planets. They were thrown into distant orbits by gravitational interactions with the giant outer planets.

  • Kukulkan

    An ancient Mayan god whose temple’s structure relates to the Mayan calendar. Each of the four faces incorporates a broad, steep staircase consisting of 91 steps that ascend to the top platform. Counting the top platform as an additional step gives a total of 365 steps: one step for each day of the year.

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