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Planet

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A celestial body moving in an elliptical orbit around a star.

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Solar System

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The collection of eight planets and their moons in orbit around the sun, together with smaller bodies such as asteroids, meteoroids, and comets.

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Astronomical Unit

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A unit of measurement equal to 149.6 million kilometers (93 million miles) the distance from the center of the earth to the center of the sun.

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Asteroid

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A small rocky body orbiting the sun, found mainly between the orbits of Mars and Jupiter.

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Comet

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A celestial object consisting of a nucleus of ice and dust. When near the sun, a 'tail' of gas and dust particles pointing away from the sun is visible.

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Meteoroid

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A small body moving in the solar system that would become a meteor if it entered the earth's atmosphere.

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Meteor

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A small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.

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Meteorite

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A meteor that survives its passage through the earth's atmosphere such that part of it strikes the ground.

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Scale Model

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A physical representation of an object, which maintains accurate relationships between all important aspects of the model, but is smaller or larger than the object it represents.

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Dwarf Planet

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A celestial body resembling a small planet but lacking certain technical criteria that are required for it to be classed as such.