Right Ascension

Right ascension (blue) and declination (green) as seen from outside the celestial sphere

• Literally: rising straight up
• Abbreviation: RA or AR (ascensio recta)

The right ascension is the angle computed from west to east on the celestial equator from the Vernal Equinox up to the intersection of the so-called Hour Circle of a celestial body with the Celestial Equator.
It is measured in time, or degrees. One hour is equivalent to 15 degrees of arc, 24 hours to 360 degrees of arc.

Together with declination the right ascension is used to determine the exact location of a celestial body. If one compares the coordinate system of the Celestial Sphere with the Earth's own coordinate system -- the former being a projection into outer space of the earth -- the right ascension is equivalent to the degree of longitude on earth.

See also

• Coordinate System

Weblinks

• Wikipedia: Right ascension