Right ascension

astronomical equivalent of longitude

Right ascension (abbreviated 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. It is the celestial counterpart to longitude. The other coordinate is the declination.

The moon, planets and stars all have their own right ascension. Many of them are listed in an almanac. Using arithmetic, the object’s right ascension and declination indicate where to look in the sky to see the object.

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