Glossaire beginning with R

Radiation pressure

Repulsive force exerted on an illuminated side of a solid, due to the transfer of part of the momentum of incident photons. It is it which, repelling the dust ejected by the comet nucleus, form their principal tail.

Radio astronomy
Branch of astronomy studying the radio emission of celestial objects. The Sun, planets, comets, some stars, the atomic, molecular or ionized interstellar gas, high-energy cosmic ray electrons, pulsars, galaxies, quasars, etc. emit radio waves.
Radio telescope
Antenna or set of antennas for radio astronomy.
Motion of a planet or comet around the Sun, or of a satellite around its planet.
Motion of a star, a planet, a satellite or a comet nucleus around its axis.