An Etymological Dictionary of Astronomy and Astrophysics
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The theory developed since the 1970s, which is based on the theories and discoveries since the 1930s, and aims at explaining the fundamental structure of matter. According to the standard model, everything in the universe is made from a few basic building blocks called fundamental particles, governed by four fundamental forces. The particles occur in two basic types, called quarks and leptons. Three of the four fundamental forces (except gravity) and their carrier particles are included in the Standard Model. The Standard Model has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time and through many experiments, the Standard Model has become established as a well-tested physics theory.

→ standard; → model; → particle; → physics.

Mechanics: The condition of a body or system at rest.

→ stationary; → phase.

The branch of physics that applies methods of → probability theory and → statistics to the behavior of large numbers of microscopic particles (such as molecules, atoms, or subatomic particles) in order to explain and predict the overall properties of the system composed of such particles.

→ statistical; → physics.

The field of → astrophysics concerned with the study of the physical characteristics of stars, more specifically their → internal structure, physical processes taking place in their interiors, atmospheres, → stellar winds, → mass loss, interaction with the → interstellar medium, as well as the physical laws governing → star formation. Same as → stellar physics and → stellar astronomy.

→ stellar; → astrophysics.

The outer envelope of gas and plasma that surrounds a star; characterized by pressure, temperature, density, chemical composition, and opacity at varying altitudes.

→ stellar; → atmosphere.

A model that computes the radiation field crossing the boundary layers of a star at all frequencies. The parameters used for the characterization of a stellar atmosphere model are: → effective temperature, → surface gravity, and → metallicity.

→ stellar; → atmosphere; → model.

The precise measurement of a star's brightness, usually through several specific wavelength bands.

→ stellar; → photometry.

Same as → stellar astrophysics.

→ stellar; → physics.

A group of five closely grouped galaxies (NGC 7317, 7318A, 7318B, 7319 and 7320) in the constellation → Pegasus. Four of the galaxies show essentially the same → redshift, suggesting that they are at the same distance from us. The fifth galaxy (NGC 7320) has a smaller redshift than the others, indicating it is much closer. This one is probably a foreground galaxy which happens to lie along the line of sight. The four distant galaxies seem to be colliding, showing serious distortions due to gravitational → tidal forces. The NASA → Spitzer Space Telescope has revealed the presence of a huge intergalactic → shock wave. Collisions play an important role in the life cycles of galaxies. → merging galaxies.

Named after the French astronomer Edouard Stéphan (1837-1923), who discovered the group in 1877 at Marseilles Observatory, using the → Foucault's reflector; → quintet.

Of, relating to, or being a delineation of the form of a solid body on a plane.

→ stereography; → -ic

A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.

→ stereographic; → projection

The process or art of depicting solid objects on a plane surface.

→ stereo- + → -graphy

Of, relating to, or determined by → stratigraphy.

→ stratum; → -graphic.

The study of → sedimentary rock units, including their geographic extent, age, classification, characteristics and formation.

→ stratum; → -graphy; → -logy.

The second major layer of Earth's atmosphere, just above the → troposphere and below the → mesosphere, extending from about 20 km to 90 km above the Earth. It is characterized by little vertical increase in temperature.

From Fr. stratosphère, literally "sphere of layers," coined by Fr. meteorologist Léon-Philippe Teisserenc de Bort (1855-1913) from L. stratus "a spreading out" (from p.p. stem of sternere "to spread out") + -sphère (→ sphere), as in atmosphère.

Cine-sepehr, from Ciné, → stratum, + sepehr, → sphere.

Of, relating to, or characteristic of the stratosphere.

→ stratosphere; → -ic.

A partnership of NASA and the German Aerospace Center, consisting of an extensively modified Boeing 747SP aircraft carrying a reflecting telescope with an effective diameter of 2.5 m. NASA Ames Research Center manages SOFIA's science and mission operations in cooperation with the Universities Space Research Association and the German SOFIA Institute. SOFIA is the largest airborne observatory in the world, with a planned 20-year lifetime.

→ stratospheric; → observatory; → infrared; → astronomy.

A theoretical sphere of → ionized hydrogen created by energetic → ultraviolet→ photons of a hot, → massive star embedded in a uniform interstellar → molecular cloud and lying at the center of the sphere. → H II region.

Named after Bengt Strömgren (1908-1987), a Danish astrophysicist, who put forward the first and simplest version of the model in 1939; → sphere.

A general term for materials of all types and sizes that are ejected by volcanic eruptions. It includes particles as tiny as volcanic ash and as large as bombs and blocks.

From Gk. tephra "ashes."

An astrophysical study or research group mainly concerned with theory rather than observation.

→ theoretical; → astrophysics.