Index :

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z .

radiation

Energy radiated in the form of waves or particles; photons.

radiationbelt

Regions of charged particles in a magnetosphere.

red giant

A star that has low surface temperature and a diameter that is large relative to the Sun.

regio

Region.

regolith

The layer of rocky debris and dust made by metoritic impact that forms the uppermost surface of planets, satellites and asteroids.

relativity, Theory of

More accurately describes the motions of bodies in strong gravitational fields or at near the speed of light than newtonian mechanics. All experiments done to date agree with relativity's predictions to a high degree of accuracy. (Curiously, Einstein received the Nobel prize in 1921 not for Relativity but rather for his 1905 work on the photoelectric effect.)

resolution

The amount of small detail visible in an image; low resolution shows only large features, high resolution shows many small details.

resonance

A relationship in which the orbital period of one body is related to that of another by a simple integer fraction, such as 1/2, 2/3, 3/5.

retrograde

The rotation or orbital motion of an object in a clockwise direction when viewed from the north pole of the ecliptic; moving in the opposite sense from the great majority of solar system bodies.

revolution

A complete rotation of a body around a central point or axis.

rhyolite

Fine-grained extrusive igneous rock, commonly with phenocrysts of quartz and feldspar in a glassy groundmass.

rhyolite

Fine-grained extrusive igneous rock, commonly with phenocrysts of quartz and feldspar in a glassy groundmass.

rift

A fracture or crack in a planet's surface caused by extension. On some volcanoes, subsurface intrusions are concentrated in certain directions; this causes tension at the surface and also means that there will be more eruptions in these "rift zones."

rift valley

An elongated valley formed by the depression of a block of the planet's crust between two faults or groups of faults of approximately parallel strike.

rima

A fissure.

Roche limit

The closest a fluid body can orbit to its parent planet without being pulled apart by tidal forces.

rupes

The term applied to scarps on planetary surfaces; many scarps are thought to be the surface expression of faults within the crust of the planetary object.

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