Right ascension (abbreviated RA; symbol α) is the astronomical term for one of the two direction coordinates of a point on the celestial sphere in the equatorial coordinate system, usually combined with declination. Right ascension's angular distance is measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question.
An old term, right ascension (Latin, ascensio recta) 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.
Other articles related to "right ascension":
... The concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC ... became widely adopted for observation, the equatorial coordinate system, which includes right ascension, was adopted at the same time for simplicity ... accurately pointed at objects with known right ascension and declination by the use of setting circles ...