Nebulae Reference Libraries

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Supernova Remnant
2004-10-19 04:45:42

Supernova Remnant -- A supernova remnant (SNR) is made up of the materials left behind by the gigantic explosion of a star in a supernova. There are two possible routes to this end: either a massive star may cease to generate fusion energy in its core, and collapse inward under the force of its own gravity, or a white dwarf star may accumulate material from a companion star until it reaches...

Star Formation
2004-10-19 04:45:42

Star Formation -- Star formation is the process by which gas in molecular clouds gets transformed into stars. In the current paradigm of star formation, cores of molecular clouds (regions of specially high density) became gravitationally unstable, and start to concentrate. Part of the gravitational energy lost in the process is radiated in the infrared, another part increases the...

Reflection Nebula
2004-10-19 04:45:42

Reflection Nebula -- In astronomy, reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. The nearby star or stars are not hot enough to cause ionization in the gas of the nebula like in emission nebulae but are bright enough to give sufficient scattering to make the dust visible. The distiction between these two types of nebulae was done by...

Planetary Nebula
2004-10-19 04:45:42

Planetary Nebula -- A planetary nebula is an astronomical object that usually appears nebulous and disk-like in low-resolution observations. Because of this appearance, similar to the appearance of planets in early observations, the "planetary" adjective was attached and has since been retained for historical consistency. According to current observations and models, planetary nebulae...

2004-10-19 04:45:42

Nebula -- in astronomy, observed manifestation of a collection of highly rarefied gas and dust in interstellar space. Prior to the 1960s this term was also applied to bodies later discovered to be galaxies, e.g., the so-called Great Nebula in the constellation Andromeda. In 1864, William Huggins confirmed William Herschel's conclusion that nebulae are not swarms of stars by determining that...

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

Molecular Cloud -- Molecular clouds are interstellar nebulae that have a density and size sufficient to permit the formation of H2, molecular hydrogen. However, this molecule is difficult to detect, and the molecule most used to trace the H2 is CO (carbon monoxide). The ratio between CO luminosity and H2 mass is roughly constant, although there are reasons to doubt this assumption in...

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

Interstellar Cloud -- Interstellar cloud is the generic name given to accumulations of gas and dust in our galaxy. Depending on the density, size and temperature of a given cloud, the hydrogen in it can be neutral (HI clouds) or molecular (molecular clouds). Chemical compositions Analysing the composition of interstellar clouds is achieved by studying electromagnetic radiation that we...

H II Region
2004-10-19 04:45:41

H II Region -- An H II region is an emission nebula associated with hot, young, blue stars, and star forming regions. H II, or singly-ionized hydrogen, is nebular gas ionized by ultraviolet light emitted by these hot, young stars of spectral type O and B. The sizes of H II regions are determined both by the amount of gas present, and by the luminosity of the O and B stars -- the more...

Emission Nebula
2004-10-19 04:45:41

Emission Nebula -- In astronomy, emission nebulae are clouds of ionized gas, emitting light of various colors. The most common source for ionization are high-energy photons emitted from a nearby young, hot star. Usually, a young star will ionize part of the same cloud from which it was born. Only big, hot stars can release the amount of energy required to ionize a significant part of a...

Trifid Nebula
2004-10-19 04:45:40

Trifid Nebula -- Discovered by Charles Messier in 1764. Charles Messier discovered this object on June 5, 1764, and described it as a cluster of stars of 8th to 9th magnitude, enveloped in nebulosity. The Trifid Nebula M20 is famous for its three-lobed appearance. This may have caused William Herschel, who normally carefully avoided to number Messier's objects in his catalog, to assign...

Word of the Day
  • One of a pair of round metal cymbals attached to the fingers and struck together for rhythm and percussion in belly dancing.
The word 'zill' comes from a Turkish word meaning "cymbals".