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Astronomical Constants| Light-year (distance traveled by light in one year) | 5,880,000,000,000 mi | | Parsec (parallax of one second, or stellar distances) | 3.259 light-years | | Velocity of light | c. 186,282.4 mi/sec | | Astronomical unit (A.U.), or mean distance Earth to Sun | ca. 93,000,000 mi1 | | Mean distance, Earth to Moon | 238,860 mi | | General precession | 50',.26 | | Obliquity of the ecliptic | 23° 27'8'.26-0'.4684(t-1900)2 | | Equatorial radius of Earth | 3963.34 statute mi | | Polar radius of Earth | 3949.99 statute mi | | Earth's mean radius | 3958.89 statute mi | | Oblateness of Earth | 1/297 | | Equatorial horizontal parallax of the moon | 57'2'.70 | | Earth's mean velocity in orbit | 18.5 mi/sec | | Sidereal year | 365d.2564 | | Tropical year | 365d.2422 | | Sidereal month | 27d.3217 | | Synodic month | 29d.5306 | | Mean sidereal day | 23h56m4s.091 of mean solar time | | Mean solar day | 24h3m56s.555 of sidereal time |
1. Actual mean distance derived from radar bounces: 92,935,700 mi. The value of 92,897,400 mi (based on parallax of 8".80) is used in calculations. 2. t refers to the year in question, for example, 2003.
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