Astronomy and related astronomical terms

A mysterious, "quasistellar", or star-like, object in a galaxy's core which is very small, very bright, and very distant: Most quasars are strong sources of radio energy.

A quasar is an exceptionally powerful, yet very compact extragalactic object, whose exact nature is still uncertain.

Observations suggest that quasars may be the hyperactive nuclei of galaxies, while theory indicates that the high luminosity which is 100 to 1,000 times that of normal galaxies, could be associated with a supermassive black hole.

Radio signals transmitted to and bounced back from an object: Radars are used especially for spotting and locating certain features on a planet.

RADAR is an acronym for RAdio Detecting And Ranging.

The bouncing of radio waves off objects in the solar system, with reception and analysis of the "echoes".

By the way of radar astronomy, radar contact with the Moon was first made in 1945 and with Venus in 1961. The travel time to radio reflections allows the distances of objects to be determined accurately.

Analysis of the reflected beam reveals the rotation period and allows the object's surface to be mapped. The rotation periods of Venus and Mercury were first determined by radar. Radar maps of Venus were obtained first by earth-based radar and subsequently by orbiting space probes.

The apparent point on the celestial sphere from which meteors making up a shower seem to emerge, as a result of a perspective effect: A radiant is the source of a meteor shower seen in the sky at night.

Energy transmitted through space as waves or particles: Two examples of radiation can be heat radiation or the splitting up of light rays.

A subfield of astronomy that deals with celestial objects at radio frequencies; a frequency that is useful for radio transmission, usually between 10 kHz and 300,000 MHz: Radio astronomy uses radio telescopes to study the celestial bodies in the sky.

In addition to celestial bodies that radiate visible light, the universe contains many objects that emit radiation of various non-visible wavelengths, such as radio waves.

Some astronomical objects emit very little light or even none at all, however they may radiate relatively large amounts of energy at non-visible wavelengths.

Radio observations of celestial objects can be made from the Earth's surface during the day and at night, both in cloudy and clear weather.

An instrument used to make observations of celestial bodies at radio wavelengths: The radio telescope usually consists of an aerial which collects the radiation and feeds it to a processing computer.

A form of electromagnetic radiation traveling at the speed of light whose frequency lies between about 10 kilohertz and about 100,000 megahertz: Radio waves are low frequency and, therefore, long wavelength electromagnetic radiations.

The radio part of the electromagnetic spectrum lies beyond the infrared region and comprises all radiation with a frequency lower than about 300,000 million hertz (300,000 MHz) or with a wavelength longer than about one millimeter.

Movement of a celestial object away from the observer: Recession can also be defined as the withdrawal of one stellar body from another celestial object.

A small, relatively cool star with low luminosity: A red dwarf is an old and cool star that is rather small compared to other stars, but it is still bigger than Jupiter, for example.

A large red colored star with a relatively low surface temperature, a few thousand degrees at most, and a radius between 10 and 100 times that of the Sun: Such red giants are representative of stars at the end of their evolutionary life.

The observed shift of the characteristic spectral lines of a galaxy, for example, toward the red, longer-wavelength, end of the spectrum as a result of the galaxy's recession from the earth: The red shift is the lengthening of the wavelengths of light from an object as a result of the object's motion away from the Earth.

It is an example of the Doppler effect. The red shift in light from galaxies is evidence that the universe is expanding.

A nebula that shines as the result of the scattering of the light of a star or group of stars nearby: A reflection nebula reflects starlight and looks blue in photographs.

Such scattering is usually caused by dust within the nebula.

A telescope that uses lenses to gather light from faint objects: The front objective lens of the refractor telescope is usually made of two or more components, with the eyepiece at the other end being the point at which the observer sees the image of the object.

The topmost layer of the Moon and arth-like planets, which has been broken up by meteoric bombardment: The regolith consists of loose rocks, dust, sand, and / or soil and is found on the bedrock or surface layer of most dry land on the Earth, Moon and other celestial objects.