Lunar distance (navigation)

lunar distance methodlunar distancemethod of lunar distanceslunar-distance methodlunar distanceslunarsdetermining longitude via eclipses of the moondistance between the moon and the sunlunar [distance]sLunar distance model
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body.wikipedia
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Celestial navigation

astronavigationnavigationcelestial
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body. In celestial navigation, knowledge of the time at Greenwich and the measured positions of one or more celestial objects allows the navigator to calculate latitude and longitude.
There are several other methods of celestial navigation that will also provide position-finding using sextant observations, such as the noon sight, and the more archaic lunar distance method.

Greenwich Mean Time

GMTGMT+4UTC±00:00
The lunar distances method uses this angle, also called a lunar, and a nautical almanac to calculate Greenwich time.
But this practice, combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, led to GMT being used worldwide as a standard time independent of location.

Marine chronometer

chronometerchronometersChronoscope
The method was published in 1763 and used until about 1850 when it was superseded by the marine chronometer.
The lunar distances method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer.

Longitude

WestlongitudinalE
In celestial navigation, knowledge of the time at Greenwich and the measured positions of one or more celestial objects allows the navigator to calculate latitude and longitude.
See Lunar distance (navigation).

Sextant

sextantsadjusting a sextantArtificial horizon sextant
Using a sextant, the navigator precisely measures the angle between the moon and another body.
A sextant can also be used to measure the lunar distance between the moon and another celestial object (such as a star or planet) in order to determine Greenwich Mean Time and hence longitude.

Nevil Maskelyne

MaskelyneMaskelyne, NevilNeville Maskelyne
After the method was first published in 1763 by British astronomer royal Nevil Maskelyne, based on pioneering work by Tobias Mayer, for about a hundred years (until about 1850) mariners lacking a chronometer used the method of lunar distances to determine Greenwich time as a key step in determining longitude.
Bad weather prevented observation of the transit, but Maskelyne used his journey to trial a method of determining longitude using the position of the moon, which became known as the lunar distance method.

Tobias Mayer

Johann MayerJohann Tobias MayerT. Mayer
After the method was first published in 1763 by British astronomer royal Nevil Maskelyne, based on pioneering work by Tobias Mayer, for about a hundred years (until about 1850) mariners lacking a chronometer used the method of lunar distances to determine Greenwich time as a key step in determining longitude.
He found these to be sufficiently accurate to determine the Moon's position to 5", and consequently the longitude at sea to about half a degree. An improved set was later published in London (1770), as also the theory (Theoria lunae juxta systema Newtonianum, 1767) upon which the tables are based. His widow, with whom they were sent to England, received in consideration from the British government a grant of £3,000 . Appended to the London edition of the solar and lunar tables are two short tracts, one on determining longitude by lunar distances, together with a description of the reflecting circle (invented by Mayer in 1752), the other on a formula for atmospheric refraction, which applies a remarkably accurate correction for temperature.

Greenwich

Greenwich, LondonGreenwich, EnglandEast Greenwich
In celestial navigation, knowledge of the time at Greenwich and the measured positions of one or more celestial objects allows the navigator to calculate latitude and longitude.
But this practice, combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, eventually led to GMT being used worldwide as a reference time independent of location.

Dead reckoning

Dead-reckonedPedestrian Dead ReckoningAutomotive dead reckoning
Captain Joshua Slocum, in making the first solo circumnavigation in 1895–1898, somewhat anachronistically used the lunar method along with dead reckoning in his navigation.
Before the 18th-century development of the marine chronometer by John Harrison and the lunar distance method, dead reckoning was the primary method of determining longitude available to mariners such as Christopher Columbus and John Cabot on their trans-Atlantic voyages.

Navigation

nauticalnavigatenavigational
Captain Joshua Slocum, in making the first solo circumnavigation in 1895–1898, somewhat anachronistically used the lunar method along with dead reckoning in his navigation.
Lacking that, one can use a sextant to take a lunar distance (also called the lunar observation, or "lunar" for short) that, with a nautical almanac, can be used to calculate the time at zero longitude (see Greenwich Mean Time).

Board of Longitude

Discovery of Longitude at Sea Act 1713Commissioner for the discovery of longitudeCommissioners for the discovery of longitude at sea
The lunar distance method was used by mariners either in conjunction with or instead of the marine chronometer.

Joshua Slocum

Capt. Joshua SlocumSlocumSlocum, Captain Joshua
Captain Joshua Slocum, in making the first solo circumnavigation in 1895–1898, somewhat anachronistically used the lunar method along with dead reckoning in his navigation.
On one long passage in the Pacific, Slocum also famously shot a lunar distance observation, decades after these observations had ceased to be commonly employed, which allowed him to check his longitude independently.

John Harrison

H-4H4H4 and H5
Many scientists, including Isaac Newton and Christiaan Huygens, doubted that such a clock could ever be built and favoured other methods for reckoning longitude, such as the method of lunar distances.

Josef de Mendoza y Ríos

José de Mendoza y Ríosde Mendoza y Ríos, JosefJosef de Mendoza y '''Ríos

Henry Raper

Lieutenant H. Raper
Amongst his achievements was his quantification of the unreliability of a key longitudinal measurement, lunar distance, when taken at different times.

Bowditch's American Practical Navigator

American Practical NavigatorThe New American Practical NavigatorBowditch
Much of Bowditch’s original content, including his methods for clearing lunar distance observations, were dropped in 1880 (though a new method for clearing lunars remained in an appendix until the early 20th century).

Angular distance

angular separationapparent distanceangular separations
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body.

Moon

lunarthe MoonLuna
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body.

Nautical almanac

almanacnavigational almanacsNavigational ephemeris tables
The lunar distances method uses this angle, also called a lunar, and a nautical almanac to calculate Greenwich time.

Galilean moons

Galilean satellitesGalilean moonmoons of Jupiter
A similar method uses the positions of the Galilean moons of Jupiter.

Jupiter

JovianGioveplanet Jupiter
A similar method uses the positions of the Galilean moons of Jupiter.

Astronomical object

celestial bodiescelestial bodycelestial object
In celestial navigation, lunar distance is the angular distance between the Moon and another celestial body. In celestial navigation, knowledge of the time at Greenwich and the measured positions of one or more celestial objects allows the navigator to calculate latitude and longitude. Using a sextant, the navigator precisely measures the angle between the moon and another body.

Latitude

latitudesSouthlatitudinal
In celestial navigation, knowledge of the time at Greenwich and the measured positions of one or more celestial objects allows the navigator to calculate latitude and longitude.

Month

calendar monthmonthssynodic month
The method relies on the relatively quick movement of the moon across the background sky, completing a circuit of 360 degrees in 27.3 days (the sidereal month), or 13.2 degrees per day.