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| the particular appearance presented by the moon or a planet at a given time |
| the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km) |
| parsec (pär'sěk') Pronunciation Key
A unit of astronomical length equal to 3.26 light-years. It is based on the distance from Earth at which a star would have a parallax of one second of arc. Its metric equivalent is about 30.8 trillion km (19.1 trillion mi). It is used in measuring distances in interstellar and intergalactic space. The closest star to Earth, Alpha Centauri, is about 1.3 parsecs away. Compare astronomical unit, light-year. |
| parsec parallax second |