Right Ascension

From Wikipedia, the free encyclopedia
Right ascension (abbreviated RA; symbol α) is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question.[1] When combined with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system.
Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the vernal equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Right ascension is measured eastward along the celestial equator from the primary direction.
An old term, right ascension (Latin, ascensio recta[2]) refers to the ascension, or the point on the celestial equator which rises with any celestial object, as seen from the Earth's equator, where the celestial equator intersects the horizon at a right angle. It is contrasted with oblique ascension, the point on the celestial equator which rises with a celestial object as seen from almost anywhere else on Earth, where the celestial equator intersects the horizon at an oblique angle.[3]

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