Astronomy Glossary
There are currently 3 names in this directory beginning with the letter R.
R
red supergiant
A supergiant with spectral type M. Red supergiants are the largest stars in the universe: if put in place of the Sun, some would touch Saturn. The two brightest red supergiants in Earth's sky are Betelgeuse and Antares.
retrograde motion
Orbital or rotational motion of an object in the direction opposite the rotation of the object's primary. The direction of rotation is determined by an inertial frame of reference such as the fixed stars. Contrast prograde motion.
right ascension
In the equatorial coordinate system, the celestial equivalent of terrestrial longitude. It divides the celestial equator into 24 hours, each of 60 minutes.
Angular distance on the celestial sphere measured eastward along the celestial equator from the equinox to the hour circle passing through the celestial object. Right ascension is usually given in combination with declination.
Angular distance on the celestial sphere measured eastward along the celestial equator from the equinox to the hour circle passing through the celestial object. Right ascension is usually given in combination with declination.
