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In astronomy, there is also a heliocentric rectangular variant of equatorial coordinates, designated x, y, z, which has: The origin at the centre of the Sun. The fundamental plane in the plane of the Earth's equator. The primary direction (the x axis) toward the March equinox.
The equatorial describes the sky as seen from the Solar System, and modern star maps almost exclusively use equatorial coordinates. The equatorial system is the normal coordinate system for most professional and many amateur astronomers having an equatorial mount that follows the movement of the sky during the night. Celestial objects are found ...
When paired with declination, these astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system. An old term, right ascension ( Latin : ascensio recta ) [ 2 ] refers to the ascension , or the point on the celestial equator that rises with any celestial object as seen from Earth 's equator ...
Similar definitions exist for satellites around other planets (see planetary coordinate systems). For heliocentric orbits, the ecliptic as the reference plane, and the FPA as the origin of longitude. The angle is measured counterclockwise (as seen from north of the ecliptic) from the First Point of Aries to the node. [2]
The equatorial coordinate system on the celestial sphere. Star position is the apparent angular position of any given star in the sky, which seems fixed onto an arbitrary sphere centered on Earth. The location is defined by a pair of angular coordinates relative to the celestial equator: right ascension (α) and declination (δ).
In astronomy and celestial navigational, 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.
Celestial coordinate systems most commonly used in astronomy are equatorial coordinates and ecliptic coordinates. These are defined relative to the (moving) vernal equinox position, which itself is determined by the orientations of the Earth 's rotation axis and orbit around the Sun .
Ecliptic coordinates are convenient for specifying positions of Solar System objects, as most of the planets' orbits have small inclinations to the ecliptic, and therefore always appear relatively close to it on the sky. Because Earth's orbit, and hence the ecliptic, moves very little, it is a relatively fixed reference with respect to the stars.