MAA Glossary

R


Radiant:
The point on the celestial sphere from which meteors of a given shower appear to radiate. The effect is due to perspective.

Retrograde motion:
Westward or backward drift of a planet resulting from the forward motion of the earth as it passes the planet.

Revolution:
The orbital motion of a body around its primary.

Rift:
An apparent division of the Milky Way caused by dark clouds of superposed dust.

Right ascension (RA):
Angle, measured eastward, from the vernal equinox to the footof a star's hour circle.

Rotation:
Turning of an object on its axis.