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In contrast, the Lunar distance (LD or ), or Earth–Moon characteristic distance, is a unit of measure in astronomy. More technically, it is the semi-major axis of the geocentric lunar orbit . The average lunar distance is approximately 385,000 km (239,000 mi), or 1.28 light-seconds ; this is roughly 30 times Earth's diameter .
In celestial navigation, lunar distance, also called a lunar, is the angular distance between the Moon and another celestial body. The lunar distances method uses this angle and a nautical almanac to calculate Greenwich time if so desired, or by extension any other time. That calculated time can be used in solving a spherical triangle.
A radar map of the distances ( ) and positions ( ) of all known stellar bodies or systems within 9 light years (ly) (for within 12 ly see this map). Their distances are entered outward from the Sun (Sol) between concentric circles, each representing one ly, and arranged clockwise in hours of right ascension. The position marks are entered ...
The locations of lunar retroreflectors left by Apollo (A) and Luna (L) missions. Retroreflectors are devices which reflect light back to its source. Six retroreflectors were left at six sites on the Moon by three crews of the Apollo program, two by remote landers of the Lunokhod program, and one by the Chandrayaan program. [1]
Radar animation of asteroid 1998 OR 2, which came within 16 lunar distances in April 2020. A list of known near-Earth asteroid close approaches less than 1 lunar distance (0.0025696 AU (384,410 km; 238,860 mi)) from Earth in 2020, based on the close approach database of the Center for Near-Earth Object Studies (CNEOS).
Lunar Laser Ranging (LLR) is the practice of measuring the distance between the surfaces of the Earth and the Moon using laser ranging. The distance can be calculated from the round-trip time of laser light pulses travelling at the speed of light , which are reflected back to Earth by the Moon's surface or by one of several retroreflectors ...
Radar animation of 2017 BQ 6 during closest approach on 7 February 2017 Radar animation of 2014 JO 25 during closest approach on 19 April 2017. An example list of near-Earth asteroids that passed or will pass more than 1 lunar distance (384,400 km or 0.00256 AU) from Earth in 2017.
The distance to which the radar can detect an object is proportional to the square root of the object's size, due to the one-over-distance-to-the-fourth dependence of echo strength. Radar could detect something ~1 km across a large fraction of an AU away, but at 8-10 AU, the distance to Saturn, we need targets at least hundreds of kilometers wide.