redshift
The frequency of a simple light wave is directly related to its colour (cf. spectrum). For the lowest frequencies of visible light, that colour is red, light of the highest frequencies appears blue. If the frequency of a light wave is shifted towards lower ...
redshift, gravitational
In general relativity, light moving away from a mass or other source of gravity experiences a shift towards lower frequencies. This is called the gravitational redshift; on the other hand, light falling towards a mass is blueshifted. Both ...
recombination
In the early universe as described by the big bang models: transition that occurs at cosmic time around 380 000 years. At this point, the universe has cooled down sufficiently for atomic nuclei and electrons to form atoms - without immediately being ripped ...
radio waves
Variety of electromagnetic radiation with frequencies of a few thousand to a few billion oscillations per second, corresponding to wave-lengths of a few kilometres to a few centimetres. True to their name, these are the electromagnetic waves that bring radio ...
radio telescope
Any antenna used for radio astronomy, for instance to observe pulsars or radio
radio galaxy
One variety of the active galactic nuclei of young galaxies, whose central region radiates extremely great amounts of energy. Radio galaxies are distinguished by radiating off extremely high energies in the form of radio waves (more than 1035 Watts), from ...
radio astronomy
Branch of astronomy dedicated to the detection and evaluation of radio waves from outer space. Such observations have led to the discoveries of radio galaxies, quasars and ...
