right ascension (R.A.) One of two coordinates commonly used to define the position of an object in the sky, the other being declination. Right ascension is the equivalent of longitude on Earth but is measured in hours, minutes, and seconds from an arbitrary point which is taken as the intersection of the celestial equator with the ecliptic. Related entry equatorial coordinates Related category • CELESTIAL MECHANICS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |