Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.
There are 2759 entries in this glossary.| Term | Definition |
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| Reflection Nebula |
A cool cloud of interstellar gas and dust that shines because the dust scatters the light from nearby stars; the cloud is not itself luminous. The spectrum of the scattered light is the same as that of the starlight, though blue light is scattered more extensively than red light since the effect depends on wavelength. A notable reflection nebula is that surrounding the stars of the Pleiades.
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| Reflectivity |
normal reflectivity.
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| Reflector 1 |
A reflecting telescope.
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| Reflector 2 |
An element in an optical, radio or other telescope, or any kind of instrument, the purpose of which is to reflect electromagnetic radiation or streams of particles.
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| Refracting Telescope |
A telescope in which the main light-collecting element is an objective lens.
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| Refractor |
refracting telescope.
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| Refractory |
A material that vaporizes only at high temperatures.
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| Regio Pl. Regiones |
A term, meaning region, used as part of some planetary place names.
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| Regolith |
The layer of loose, fine-grained, soil-like material on the surface of the Moon, or similar material on any other planetary body.
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| Regression Of Nodes |
The gradual westward movement of the nodes where the Moon’s orbit intersects the ecliptic. A full circuit takes 18.61 years, and the phenomenon is due to the gravitational influence of the Sun.
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| Regular Satellite |
A natural satellite of a planet in a direct rather than retrograde orbit of low or moderate eccentricity in the planet’s equatorial plane.
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| Regulus Alpha Leonis; α Leo |
The brightest star in the constellation Leo. It is a B star of magnitude 1.4; the system is at least triple, the primary having companions of seventh and thirteenth magnitudes. The name is Latin and means little king. Regulus is sometimes known as The Royal Star.
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| Relativistic |
Having a velocity close to that of light ; Special Relativity must be used in any calculations involving such velocities and physical theory. The expression ultrarelativistic does not mean faster than light; it is used for particles travelling so fast that their kinetic energy is thousands of times higher than their rest mass energy.
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| Relativity |
General Relativity, Special Relativity.
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| Remote Sensing |
The study of the Earth or other astronomical objects by observation or probing from a distance rather than direct contact and exploration. The term is used particularly for the study of the Earth, or other bodies, from orbiting satellites. Methods include both direct, high-resolution imaging and radar.
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