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Meridian (astronomy) The meridian on the celestial sphere. An observer's upper meridian, a semicircle contains their zenith and both celestial poles; the observer's local meridian is the semicircle that passes through their zenith and the north and south points of their horizon. In astronomy, the meridian is the great circle passing through the ...
Meridian altitude is the simplest calculation of celestial navigation, in which an observer determines his latitude by measuring the altitude of an astronomical object at the time of its meridian contact. A meridian contact is the moment when the object contacts the observer's meridian, i.e. the imaginary line running north–south and through ...
The central meridian is the meridian going through the sub-Earth point. [2] Because of the body's rotation and orbital alignment with the observer the central meridian changes with time, as it is based on the observer's point of view. For example, consider the Earth as seen from the Moon. There will be a meridian going through the centre of the ...
In astronomy, the altitude in the horizontal coordinate system and the zenith angle are complementary angles, with the horizon perpendicular to the zenith. The astronomical meridian is also determined by the zenith, and is defined as a circle on the celestial sphere that passes through the zenith, nadir, and the celestial poles.
Astronomical coordinate systems. A star 's galactic, ecliptic, and equatorial coordinates, as projected on the celestial sphere. Ecliptic and equatorial coordinates share the March equinox as the primary direction, and galactic coordinates are referred to the galactic center. The origin of coordinates (the "center of the sphere") is ambiguous ...
The meridian passage is the moment when a celestial object passes the meridian of longitude of the observer. At this point, the celestial object is at its highest point. When the Sun passes two times an altitude while rising and setting can be averaged to give the time of meridian passage.
The Greenwich meridian is a prime meridian, a geographical reference line that passes through the Royal Observatory, Greenwich, in London, England. [ 1] From 1884 to 1974, the Greenwich meridian was the international standard prime meridian, used worldwide for timekeeping and navigation. The modern standard, the IERS Reference Meridian, is ...
Longitude by chronometer is a method, in navigation, of determining longitude using a marine chronometer, which was developed by John Harrison during the first half of the eighteenth century. It is an astronomical method of calculating the longitude at which a position line, drawn from a sight by sextant of any celestial body, crosses the ...