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Finding Greenwich time while at sea using a lunar distance. The lunar distance is the angle between the Moon and a star (or the Sun). In the above illustration the star Regulus is used. The altitudes of the two bodies are used to make corrections and determine the time. In celestial navigation, lunar distance, also called a lunar, is the ...
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 .
A scroll in the lower left panel of the map is inscribed with instructions on how to use the map and a lunar distance measurement to calculate longitude: it states that by observing the edge of the Moon's disc in relation to a known star, or a lunar eclipse, it is possible to calculate longitude at the point of observation by calculating local ...
The modeling problem involves two aspects: an accurate computation of the lunar orbit and lunar orientation, and an accurate model for the time of flight from an observing station to a retroreflector and back to the station. Modern Lunar Laser Ranging data can be fit with a 1 cm weighted rms residual.
A diagram of a typical nautical sextant, a tool used in celestial navigation to measure the angle between two objects viewed by means of its optical sight. Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the ...
Sunrise occurs at the prime meridian when the Lunar phase reaches First Quarter, after one fourth of a lunar day. At this location the selenographic colongitude at sunrise is defined as 0°. Thus, by the time of the Full Moon the colongitude increases to 90°; at Last Quarter it is 180°, and at the New Moon the colongitude reaches 270°.
The poles are located at ±90° from the fundamental plane. The primary direction is the starting point of the longitudinal coordinates. The origin is the zero distance point, the "center of the celestial sphere", although the definition of celestial sphere is ambiguous about the definition of its center point.
This north-south variation of the point along the horizon is bookended by two lunar standstills or turnarounds, the directions of which are sometimes depicted in archaeoastronomical constructions. [4] It takes 18.6 years for the Moon to traverse this variation viewed from a vantage point on Earth.
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