Astronomy Reference Libraries

Page 10 of about 169 Articles
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...

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

Star Catalogue -- In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Most of the recent catalogues are available in electronic format and can be freely downloaded from NASA's Astronomical...

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

Star Designation -- The International Astronomical Union (IAU) is the internationally recognised authority for assigning designations to stars (and other celestial bodies). Many of the star names in use today were inherited from the time before the IAU existed. Other names, mainly for variable stars (including novae and supernovae), are being added all the time. Most stars, however,...

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

Star Cluster -- Star clusters are physically bound systems of stars. In order of low compactness to high compactness (and in some sense also age) they range from stellar associations to open clusters to globular clusters. Star clusters are held together by the gravitation of their members. Due to both external (encounters with massive objects, influence of the host galaxy) and internal...

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...

Spiral Galaxy
2004-10-19 04:45:42

Spiral Galaxy -- Among the galaxies, there are apparently three main categories, according to their appearance: the disk galaxies (`cosmic frisbies' according to P. Murdin, D. Allen, and D. Malin), consisting of a huge disk of stars and interstellar matter, which may form interesting patterns, the elliptical galaxies (`cosmic footballs') which are uniformly looking, ellipsoidal agglomerations...

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

Solar Nebula -- In astronomy, the solar nebula is the gaseous cloud from which, in the so-called nebular hypothesis of the origin of the solar system, the Sun and planets formed by condensation. In 1755 the German philosopher Immanuel Kant suggested that a nebula in slow rotation, gradually pulled together by its own gravitational force and flattened into a spinning disk, gave birth to the...

2004-10-19 04:45:42

Photosphere -- The photosphere of an astronomical object is the region at which the optical depth becomes one. In other words, the photosphere is the place where an object stops being transparent. It is typically used to describe the Sun or another star. Because stars are large balls of gas, they have no solid surface. However, there is a depth at which the gas stops being transparent to...

Gas Giant
2004-10-19 04:45:41

Gas Giant -- A gas giant is a generic astronomical term invented by the science fiction writer James Blish to describe any large planet that is not composed mostly of rock or other solid matter. Gas giants may still have a solid core - in fact, it is expected that such a core is probably required for a gas giant to form - but the majority of its mass is in the form of gas (or gas compressed...

Extrasolar Planet
2004-10-19 04:45:41

Extrasolar Planet -- An extrasolar planet is a planet orbiting around a star other than the Sun. Extrasolar planets were first discovered in the 1990s as a result of improved telescope technology, CCD and computer-based image processing which allowed far more accurate measurements of stellar motions. The first extrasolar planets were reported by the astronomer Aleksander Wolszczan in 1993,...

Word of the Day
  • A serpent whose bite was fabled to produce intense thirst.
The word 'dipsas' comes from a Greek word meaning 'thirst'.