Lunar distance (astronomy)
In astronomy, a lunar distance (LD) is a measurement of the distance from the Earth to the Moon. The average distance from Earth to the Moon is 384,400 km (238,900 mi). The actual distance varies over the course of the orbit of the moon, from 356,700 km (221,600 mi) at the perigee and 406,300 km (252,500 mi) at apogee.
The Moon is spiraling away from Earth at an average rate of 3.8 cm (1.5 in) per year, as detected by the Lunar Laser Ranging Experiment. The recession rate is considered anomalously high. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also 3.8 cm (1.5 in).
The tidal dissipation rate varied in the Earth geological history.
The first person to measure the distance to the Moon was the 2nd-century-BC astronomer and geographer Hipparchus, who exploited the lunar parallax using simple trigonometry. He was approximately 26,000 km (16,000 mi) off the actual distance, an error of about 6.8%.
The NASA Near Earth Object Catalog includes the distances of asteroids and comets measured in Lunar Distances.
See also 
- NASA Staff (10 May 2011). "Solar System Exploration - Earth's Moon: Facts & Figures". NASA. Retrieved 2011-11-06.
- http://curious.astro.cornell.edu/question.php?number=124 Is the Moon moving away from the Earth?
- C.D. Murray & S.F. Dermott (1999). Solar System Dynamics. Cambridge University Press. p. 184.
- Dickinson, Terence (1993). From the Big Bang to Planet X. Camden East, Ontario: Camden House. pp. 79–81. ISBN 0-921820-71-2.
- Bills, B.G., and Ray, R.D. (1999), "Lunar Orbital Evolution: A Synthesis of Recent Results", Geophysical Research Letters 26 (19): 3045–3048, doi:10.1029/1999GL008348
- http://isotope.colorado.edu/~geol5700/Bills_1999.pdf - Lunar orbital evolution
- NEO Earth Close Approaches
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