What is "lunar distance"

Lunar \Lu"nar\ (l[=u]"n[~e]r), a. [L. lunaris, fr. luna the moon. See Luna, and cf. Lunary.]

1. Of or pertaining to the moon; as, lunar observations.

2. Resembling the moon; orbed.
   --Dryden.

3. Measured by the revolutions of the moon; as, a lunar month.

4. Influenced by the moon, as in growth, character, or properties; as, lunar herbs. --Bacon. Lunar caustic (Med. Chem.), silver nitrate prepared to be used as a cautery; -- so named because silver was called luna by the ancient alchemists. Lunar cycle. Same as Metonic cycle. See under Cycle. Lunar distance, the angular distance of the moon from the sun, a star, or a planet, employed for determining longitude by the lunar method. Lunar method, the method of finding a ship's longitude by comparing the local time of taking (by means of a sextant or circle) a given lunar distance, with the Greenwich time corresponding to the same distance as ascertained from a nautical almanac, the difference of these times being the longitude. Lunar month. See Month. Lunar observation, an observation of a lunar distance by means of a sextant or circle, with the altitudes of the bodies, and the time, for the purpose of computing the longitude. Lunar tables.

   1. (Astron.) Tables of the moon's motions, arranged for computing the moon's true place at any time past or future.

   2. (Navigation) Tables for correcting an observed lunar distance on account of refraction and parallax.

      Lunar year, the period of twelve lunar months, or 354 days, 8 hours, 48 minutes, and 34.38 seconds.

Distance \Dis"tance\, n. [F. distance, L. distantia.]

1. The space between two objects; the length of a line, especially the shortest line joining two points or things that are separate; measure of separation in place.

   Every particle attracts every other with a force . . . inversely proportioned to the square of the distance.
   --Sir I. Newton.

2. Remoteness of place; a remote place.

   Easily managed from a distance.
   --W. Irving.

   'T is distance lends enchantment to the view.
   --T. Campbell.

   [He] waits at distance till he hears from Cato.
   --Addison.

3. (Racing) A space marked out in the last part of a race course.

   The horse that ran the whole field out of distance.
   --L'Estrange.

   Note: In trotting matches under the rules of the American Association, the distance varies with the conditions of the race, being 80 yards in races of mile heats, best two in three, and 150 yards in races of two-mile heats. At that distance from the winning post is placed the distance post. If any horse has not reached this distance post before the first horse in that heat has reached the winning post, such horse is distanced, and disqualified for running again during that race.

4. (Mil.) Relative space, between troops in ranks, measured from front to rear; -- contrasted with interval, which is measured from right to left. ``Distance between companies in close column is twelve yards.''
   --Farrow.

5. Space between two antagonists in fencing.
   --Shak.

6. (Painting) The part of a picture which contains the representation of those objects which are the farthest away, esp. in a landscape.

   Note: In a picture, the

   Middle distance is the central portion between the foreground and the distance or the extreme distance. In a perspective drawing, the

   Point of distance is the point where the visual rays meet.

7. Ideal disjunction; discrepancy; contrariety.
   --Locke.

8. Length or interval of time; period, past or future, between two eras or events.

   Ten years' distance between one and the other.
   --Prior.

   The writings of Euclid at the distance of two thousand years.
   --Playfair.

9. The remoteness or reserve which respect requires; hence, respect; ceremoniousness.

   I hope your modesty Will know what distance to the crown is due.
   --Dryden.

   'T is by respect and distance that authority is upheld.
   --Atterbury.

10. A withholding of intimacy; alienation; coldness; disagreement; variance; restraint; reserve.

    Setting them [factions] at distance, or at least distrust amongst themselves.
    --Bacon.

    On the part of Heaven, Now alienated, distance and distaste.
    --Milton.

11. Remoteness in succession or relation; as, the distance between a descendant and his ancestor.

12. (Mus.) The interval between two notes; as, the distance of a fourth or seventh.

    Angular distance, the distance made at the eye by lines drawn from the eye to two objects.

    Lunar distance. See under Lunar.

    North polar distance (Astron.), the distance on the heavens of a heavenly body from the north pole. It is the complement of the declination.

    Zenith distance (Astron.), the arc on the heavens from a heavenly body to the zenith of the observer. It is the complement of the altitude.

    To keep one's distance, to stand aloof; to refrain from familiarity.

    If a man makes me keep my distance, the comfort is he keeps his at the same time.
    --Swift.

n. (context astronomy English) A measurement of the distance from the Earth to the Moon.

Lunar distance may refer to:

• Lunar distance (astronomy), the distance between the Earth and the Moon.
• Lunar distance (navigation), a measurement used in the calculation of longitude.

Lunar distance is as a unit of measure in astronomy. It is the average distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the geocentric lunar orbit. It may also refer to the time-averaged distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth-Moon distance.

Lunar distance is also called Earth-Moon distance, Earth–Moon characteristic distance, or distance to the Moon, and commonly indicated with LD or Δ. The mean semi-major axis has a value of . The time-averaged distance between Earth and Moon centers is . The actual distance varies over the course of the orbit of the Moon, from at the perigee to at apogee, resulting in a differential range of .

Lunar distance is commonly used to express the distance to near-Earth object encounters. Lunar distance is also an important astronomical datum; the precision of this measurement to a few part in a trillion has useful implications for testing gravitational theories such as general relativity, and for refining other astronomical values such as Earth mass, Earth radius, and Earth's rotation. The measurement is also useful in characterizing the lunar radius, the mass of the Sun and the distance to the Sun.

Millimeter- precision measurements of the lunar distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon.

The Moon is spiraling away from the Earth at an average rate of per year, as detected by the Lunar Laser Ranging Experiment. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also .

In celestial navigation, lunar distance is the angle between the Moon and another celestial body. The lunar distances method uses this angle, also called a lunar, and a nautical almanac to calculate Greenwich time. By comparing that calculated time to the measured local time, the navigator can determine longitude. The method was used for some time during the 18th century, before the introduction of the marine chronometer. A similar method uses the positions of the Galilean moons of Jupiter.