Glossary
the angular height of a celestial object above the horizon, measured in degrees from 0° at the horizon to 90° at the zenith; one of the coordinates used in the horizon system, the other being azimuth |
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point in a planet's, comet's, or asteroid's orbit around the sun when it is farthest from the sun |
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celestial body that orbits the sun and is mostly rocky in nature; most are located in a region between Mars and Jupiter; various subgroups (based on orbits) have also been identified |
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the angular measure along the horizon starting with 0° at North and measuring 90° at East, 180° at South, and 270° at West; one of the coordinates in the horizon system, the other being altitude |
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a huge cloud of dust and gas surrounding the nucleus of a comet: the coma is formed when ices in the nucleus sublimate as the comet approaches perihelion |
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celestial body that orbits the sun in an orbit that is more eccentric than the nearly circular orbits of the planets and consists mostly of various ices; these bodies consist of three major parts: the nucleus, coma and tail |
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celestial coordinate similar to latitude and used in the equatorial system along with RA; measured from 0° at the celestial equator to ±90° at the celestial poles |
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the plane of the earth's orbit; the plane of the solar system; the apparent path of the sun through the sky |
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coordinates, similar to latitude and longitude, used to describe the position of stars, planets and other celestial objects;these coordinates are independent of the observer |
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the line between the sky and ground |
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coordinates used to describe the position of a celestial object based on the observer |
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A very tiny piece of dust, often the dust from a comet. While in space, it is a meteoroid. When it collides with the Earth's atmosphere, it is a meteor (aka shooting star). If the piece is large enough to survive and land, it is a meteorite. |
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central core region of a comet believed to be composed primarily of various ices and dirt |
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the path of a celestial object around another object, ie, the planets' path around the sun or a moon's path around it's planet |
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point in the orbit when a planet, comet, or asteroid, is closest to the sun; similarly, perigee is when the Moon or a manmade satellite is closest to the Earth |
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right ascension, celestial coordinate similar to longitude and used in the equatorial system along with declination; measured in hours from 0 to 24; the 0 hour mark is based on the location of the Vernal Equinox |
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change of state from solid to gas without becoming a liquid |
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gas and dust that stream away from comet nucleus |
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the point in the sky directly overhead an observer |