Glossary R

Radiant: The point in the sky from which the tracks of meteors that are members of a particular shower appear to radiate.

Radio Telescope: An instrument that is designed to detect radio waves from astronomical sources.

Red-Dwarf Star: A cool, red, low luminosity star.

Red-Giant Star: A large, highly luminous star with a low surface temperature and a reddish colour.

Red Shift: The displacement of spectral lines to longer wavelengths that is observed when a light source is receding from an observer.

Red Supergiant Star: A extremely large star of very high luminosity and low surface temperature.

Reflecting Telescope: A telescope that uses a concave mirror to collect light, reflect light rays to a focus and form an image of a distant object.

Refracting Telescope: A telescope that uses a lens to refract (bend) light rays in order to bring them to a focus and form an image of a distant object.

Rocky Planet: A planet (also called a terrestrial planet) that is composed mainly of rocks and has similar basic characteristics to Earth.