Astronomy Reference Libraries

Page 9 of about 169 Articles
White Dwarf
2004-10-19 04:45:43

White Dwarf -- A white dwarf is a a star supported by electron degeneracy. A star like our Sun will become a white dwarf when it has exhausted its nuclear fuel. Near the end of its nuclear burning stage, such a star goes through a red giant phase and then expels most of its outer material (creating a planetary nebula) until only the hot (T > 100,000 K) core remains, which then settles...

Variable Star
2004-10-19 04:45:43

Variable Star -- Most stars are of nearly constant luminosity. Our own Sun is a good example which goes through practically no measurable variation in brightness. There are, however, stars which do vary in brightness, called variable stars. They fall into two main groups: Intrinsic variables These are stars which have intrinsic variations in brightness, that is the star itself gets...

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

Triple Star -- A triple star system consists of three gravitationally bound stars. The stars are in orbits around a common center of mass, usually so that two of the stars form a close binary star and the third is further away. This configuration is often called a hierarchical triple star. Multiple stars containing more than three stars can usually be decomposed to binaries and...

Terrestrial Planet
2004-10-19 04:45:42

Terrestrial Planet -- A terrestrial planet is a planet that is mostly composed of silicate rocks and may or may not have a relatively thin atmosphere. The term is derived from the Greek word for Earth, so an alternate definition would be those planets that are more Earth-like than not. Terrestrial planets are very different from gas giants, which may or may not have solid surfaces and...

T Tauri
2004-10-19 04:45:42

T Tauri -- T Tauri stars are a class of stars thought to represent extremely young pre-main sequence stars, in an early stage of life. They are seen near many molecular clouds in our galaxy. The first ones were found in 1945, identified by their optical variability and strong chromospheric lines. T Tauri stars have masses and temperatures similar to the Sun, but are significantly...

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

Supernova -- A supernova is a star that increases its brightness drastically within a matter of days, making it appear as if a "new" star was born (hence "nova"). The "super" prefix distinguishes it from a mere nova, which also involves a star increasing in brightness, though to a lesser extent and through a much different mechanism. Astronomers have classified supernovae in several...

Supermassive Black Hole
2004-10-19 04:45:42

Supermassive Black Hole -- A Supermassive black hole is a black hole with a mass in the range of millions or billions solar masses. A supermassive black hole has some interesting properties differing from his low-mass cousins: -- The average density of a supermassive black hole can be very low, and actually can be lower than water's density. This happens because the black hole...

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

Supergiant Star -- A star of 15 solar masses exhausts its hydrogen in about one-thousandth the lifetime of our sun. It proceeds through the red giant phase, but when it reaches the triple-alpha process of nuclear fusion, it continues to burn for a time and expands to an even larger volume. The much brighter, but still reddened star is called a red supergiant. Betelgeuse, at the shoulder...

Stellar Evolution
2004-10-19 04:45:42

Stellar Evolution -- Stellar evolution is the process of formation, life, and death of stars. It is one of the major topics of cosmogony. Star Birth and Life A star starts out as an enormous cloud of gas and dust many light-years across. Star formation begins when the cloud begins to condense under its own gravity. The processes that initiate this contraction are not fully understood....

Word of the Day
  • In dressmaking, straps running from the belt in front over the shoulders to the belt in the back, with more or less elaboration of trimming and outline. They usually broaden at the shoulder and narrow toward the waist.
The word 'bretelles' comes from a French word meaning 'braces'.