Right ascension (abbrev. RA; symbol α) is the astronomical word for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.
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How right ascension got its name. Ancient astronomy was very concerned with the rise and set of celestial objects. The ascension was the point on the celestial equator (red) which rose or set at the same time as an object (green) on the celestial sphere. As seen from the equator, both were on a great circle from pole to pole (left, sphaera recta or right sphere). From almost anywhere else, they were not (center, sphaera obliqua or oblique sphere). At the poles, objects did not rise or set (right, sphaera parallela or parallel sphere). An object's right ascension was its ascension on a right sphere.
See also
In Spanish: Ascensión recta para niños
