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Last updated on April 17, 2014 at 12:17 EDT

Universe

Ring Galaxy -- A subclass of interacting galaxies, ring galaxies, provides a unique laboratory for studying unusually large bursts of non-nuclear star formation. The rings in these systems are often large (10s of kiloparsecs) and contain what appea...

Seyfert Galaxy -- Seyfert galaxies are spiral or irregular galaxies containing an extremely bright nucleus, most likely caused by a supermassive black hole, that can sometimes outshine the surrounding galaxy. The light from the central nucleus vari...

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 suggeste...

Space -- The definition of space in physics is contentious. Various concepts used to try to define space have included: -- the structure defined by the set of "spatial relationships" between objects -- a manifold defined by a coordinate system ...

Spacetime -- In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional manifold called spacetime (alternatively, space-time; see below). A point in spacetime may be referred to ...

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 ma...

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 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 tog...

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...

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 frequ...

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, ...

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...

Strange Matter -- Strange matter (also known as quark matter) is an ultra-dense phase of matter that is theorized to form inside particularly massive neutron stars (which are then known as "strange stars" or "quark stars"). It's theorized that when...

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 ...

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 ...

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 incr...

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 c...

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 op...

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 plan...

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 configurati...