Welcome to the Astronomy Dictionary Page. As you begin learning about Astronomy, you'll find words and terms you don't know. If you find a word or term on this site that's new to you, just come back to this Astronomy Dictionary Page and look it up.
Ablation - The burning away of the surface of an object. When a meteorite enters the Earth's atmosphere, ablation occurs.
Absolute Magnitude - The absolute magnitude of a star is the apparent magnitude of that object if it were 10 parsecs away
Absorption Spectrum - An electromagnetic spectrum, broken by a pattern of lines when radiation passes through a particular medium.
Aperture - An adjustable opening in a telescope that limits the light that can pass through the lense or mirror.
Asterism - A grouping of stars smaller than a constellation.
Asteroid Belt -The region between Mars and Jupiter that contains mostly asteroids.
Astronomy -The study of the position and movements of celestial objects in space.
Astronomical Unit - Unit of measure used to measure distance in the Solar System. Approximately 93 million miles.
Astronaut - A highly trained person who travels in a spacecraft.
Atmosphere - The gases that surround a celestial body such as Earth.
Axis - An imagined straight line about which a planet rotates.
Binary Star - A system of two stars which revolve around one another.
Black Hole - An area of outer space with an extremely high gravitational field caused by a collapsed star.
Calendar - Various systems of timekeeping that track the beginning, length, and divisions of a year.
Comet - A small celestial body made of ice, dirt, and other particles that travels in an elliptical orbit around the Sun.
Constellation - A grouping of stars which form a pattern in the sky.
Cosmology - The study of the universe as a whole and its origins.
Eclipse - When one celestial body obscures the view of another.
Ellipse - A closed plane curve which comes from the intersection of a cone and a plane which cuts though it.
Emission Nebula - Nebula which absorbs the ultraviolet radiation of nearby stars and emits it as light.
Equatorial Mount - A telescope mount with two perpendicular axes, one is parallel to the Earth's rotation axis.
Escape Velocity -The velocity an object has to reach to break the gravitational field of a celestial body.
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Facula - An area on the visible surface of the Sun that is brighter than the surrounding area.
Galaxy - A cluster of gas, dust, and, stars which is thousands of parsecs across.
Greenhouse Effect - The trapping of infrared radiation from the surface of a planet by a dense atmosphere.
Heliocentric - The theory that puts the Sun at the center of our Solar System.
Ion - An atom or group of atoms which by either gaining or losing an electron, becomes either positively or negatively charged.
Kepler Laws - Three laws of planetary motion. (a) The orbit of a planet is an ellipse with the Sun at one focus. (b) The line joining the position of a planet to the Sun sweeps out equal areas at equal times. (c) The squares of the orbital periods of the planets are proportional to the cube of their mean distances to the Sun.
Light Year - A measure of distance equal to the distance that light travels in one year.
Meteor - The streak of light seen in the night sky when a meteorite burns up in the Earth's atmosphere.
Milky Way - A faint band of light that can be seen stretching across the celestial plane. This area contains the stars that are in the center plane of our galaxy.
Orbit - The path followed by one celestial object around another because of mutual gravitational attraction.
Solar System - The Sun and all the planets.
Universe - All of space and matter in existence.
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This Astronomy Dictionary Page should give you a basic understanding of some of the common Astronomy terms people use. Once again, if you come upon a term on this site you dont know, just come back to the Astronomy Dictionary Page.