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In astronomy, the meridian is the great circle passing through the celestial poles, as well as the zenith and nadir of an observer's location. Consequently, it contains also the north and south points on the horizon , and it is perpendicular to the celestial equator and horizon.
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. A zenith telescope is a type of telescope designed to point straight up at or near the zenith, and used for precision measurement of star positions, to simplify telescope ...
Meridian altitude is the simplest calculation of celestial navigation. An observer determines their latitude by measuring the altitude of an astronomical object at the time of its meridian transit. A meridian is the imaginary plane running north–south and through the zenith, nadir, and celestial poles.
An object on the meridian to the south of the observer has A = h = 0° with this usage. However, n Astropy's AltAz, in the Large Binocular Telescope FITS file convention, in XEphem, in the IAU library Standards of Fundamental Astronomy and Section B of the Astronomical Almanac for example, the azimuth is East of North.
In astronomy and celestial navigation, the hour angle is the dihedral angle between the meridian plane (containing Earth's axis and the zenith) and the hour circle (containing Earth's axis and a given point of interest). [1] It may be given in degrees, time, or rotations depending on the application.
Right ascension is usually measured in sidereal hours, minutes and seconds instead of degrees, a result of the method of measuring right ascensions by timing the passage of objects across the meridian as the Earth rotates. There are 360° / 24 h = 15° in one hour of right ascension, and 24 h of right ascension around the entire ...
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In other words, the prime vertical is the vertical circle perpendicular to the meridian, and passes through the east and west points, zenith, and nadir of any place. [2] A heavenly body is in or on the prime vertical when it bears true east or true west—when it is at right angles to the meridian.