A unit of measurement equal to 149.6 million kilometers, the mean distance from the center of the earth to the center of the sun.
- Bodies that formed from the Sun out to a distance of about 2.5 astronomical units are primarily rocky and metallic.
- Typical distances from the Sun are 10,000 astronomical units, and typical orbital periods are on the order of 1 million years.
- Today the distance between the Earth and sun, known as an astronomical unit, is accurately measured by radar.
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Syllabification: as·tro·nom·i·cal u·nit
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