Nebula 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...

2004-10-19 04:45:42

Star -- A star is a self-gravitating sphere of plasma in hydrostatic equilibrium that generates energy in its interior through the process of nuclear fusion. Energy from this process radiates into space as electromagnetic radiation and neutrinos. Star formation and evolution As learned by star formation astronomers, stars are born in molecular clouds, regions of higher density of...

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...

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...

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

Saturn Nebula -- The layers of the Saturn Nebula give a complex picture of how this planetary nebula was created. The above picture, taken in April 1996 and released last week, allows a better understanding of the mysterious process that transformed a low-mass star into a white dwarf star. A computer model indicates that the central star of NGC 7009 first expelled the green gas that now...

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

Rosette Nebula -- Discovered by John Flamsteed about 1690. The Rosetta Nebula is a vast cloud of dust and gas, extending over an area of more than 1 degree across, or about 5 times the area covered by the full moon. Its parts have been assigned different NGC numbers: 2237, 2238, 2239, and 2246. Within the nebula, open star cluster NGC 2244 is situated, consisted of the young stars which...

Word of the Day
  • A person in a secondary role, specifically the second most important character (after the protagonist).
The word 'deuteragonist' comes from a Greek word meaning 'an actor of second-class parts'.