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Astronomy Reference Libraries

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Active Galaxy
2004-10-19 04:45:41

Active Galaxy -- An active galaxy is a galaxy where a significant fraction of the energy output is not emitted from normal stellar populations or interstellar gas. This energy, depending on the active galaxy type, can be emitted across most of the electromagnetic spectrum, as infrared, radio waves, UV, X-ray and gamma rays. Frequently, the abbreviation AGN (Active Galactic Nuclei) is...

Accretion Disk
2004-10-19 04:45:41

Accretion Disk -- An accretion disk is a structure formed by material falling into a gravitational source. Conservation of angular momentum requires that, as a large cloud of material collapses inward, any small rotation it may have will increase. Centrifugal force causes the rotating cloud to collapse into a disk, and tidal effects will tend to align this disk's rotation with the rotation...

Accelerating Universe
2004-10-19 04:45:41

Accelerating universe -- In the late 1990s, observations of type I supernova produced the unexpected result that the expansion of the universe appears to be accelerating. These observations appear more firm as new data has appeared. This means that the speed with which a distant galaxy recedes from us increases over time. If this trend continues, eventually we won't be able to see any...

Van Allen Radiation Belt
2004-10-19 04:45:41

Van Allen Radiation Belt -- The Van Allen radiation belt is a torus of energetic charged particles around Earth, trapped by Earth's magnetic field. The presence of a radiation belt had been theorized prior to the Space Age and the belt's presence was confirmed by the Explorer I on January 31, 1958 and Explorer III missions, under Doctor James Van Allen. The trapped radiation was first mapped...

Solar System
2012-10-22 06:09:41

The Solar System refers to the area in space that is dominated by our own Sun. It is comprised of the Sun and its associated astronomical objects that are held in its gravitational orbit. The Solar System was formed as a result of the collapse of a giant molecular cloud approximately 4.6 billion years ago. The mass of this system is located almost entirely in the Sun. Apart from the Sun, a high...

Solar Eclipse
2004-10-19 04:45:41

Solar Eclipse -- A solar eclipse occurs when Sun, Moon and Earth are on a single line, the Moon being in the middle. Seen from the Earth, the Moon is in front of the Sun and thus part or all of the light of the Sun is hidden by the Moon. Thus it may seem that a piece has been taken out of the Sun, or that it has suddenly disappeared. There are three types of solar eclipses: -- A partial...

Oort Cloud
2004-10-19 04:45:41

Oort Cloud -- The Oort cloud is a postulated cloud of comets situated about 50,000 to 100,000 AU from the sun. Although no direct observations have been made of such a cloud, it is believed to be the source of most or all comets entering the inner solar system (some short-period comets may come from the Kuiper belt), based on observations of the orbits of comets. The Oort cloud was...

Kuiper Belt
2004-10-19 04:45:41

Kuiper Belt -- The Kuiper belt is an area of the solar system extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. The largest of the objects in the Kuiper belt are the planet Pluto and its moon Charon. A new Kuiper belt object, currently called 2001 KX76, has been found that is about the size of Charon, and larger than Ceres. Another such object, Quaoar, discovered in 2002,...

Asteroid Belt
2004-10-19 04:45:41

Asteroid Belt -- The Asteroid belt is a region of the solar system falling roughly between the planets Mars and Jupiter where the greatest concentration of asteroid orbits can be found. It is believed that, during the first million years of the solar system history, planets formed by accretion of planetesimals. Ripetute collisions led to the familiar rocky planets and to the gas giant's...

Pluto
2004-10-19 04:45:41

Planet Pluto -- Pluto is the ninth and smallest planet of our solar system. It was discovered by the astronomer Clyde Tombaugh at the Lowell Observatory in Arizona on February 18, 1930 (although the body was first photographed on March 19, 1915). Tombaugh was searching for a "Planet X" to explain the orbit of Neptune; further analysis, with seven decades more data about Neptune's position,...

Word of the Day
megalophonous
  • Having a loud voice; vociferous; clamorous.
  • Of grand or imposing sound.
The word 'megalophonous' comes from Greek roots meaning 'big' and 'sound'.