An Etymological Dictionary of Astronomy and Astrophysics
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A listing of stars usually ordered by right ascension with observational data elements such as coordinates, magnitude, distance, proper motion, and so on.

→ star; → catalog.

A chart or map showing the relative apparent positions of the stars as viewed from the Earth.

→ star; chart, from M.Fr. charte "card, map," from L. charta "leaf of paper, tablet," from Gk. khartes "layer of papyrus."

Negâré, from negâr "picture, figure," from negâštan→ Pictor; setâregân plural of setâré→ star.

1) A group of stars held together by the mutual → gravitational attraction of its members, which are physically related through common origin. They are of two types: → open clusters and → globular clusters.
2) A → bound stellar agglomeration for which the age of the stars exceeds the → crossing time (Giels & Portegies Zwart, 2010, MNRAS Letters, astro-ph/1010.1720). See also → stellar association

→ star; → cluster.

The number of stars that appear in a given region of sky, usually counted on a photographic plate or CCD image.

→ star; → count.

The relative motion of two groups of stars in the Galaxy moving in opposite directions.

→ star; → drift.

The process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy, star formation includes the study of the interstellar medium and molecular clouds as precursors to the star formation process as well as the study of young stellar objects.

→ star; → formation.

The degree to which stars form in a system, such as a → molecular cloud or a → galaxy. It is given by the ratio of the total mass of stars to the initial gas mass: ε_SFE = M_stars / (M_stars + M_gas).

→ star formation; → efficiency.

The → star formation rate as a function of time.

→ star; → formation; → history.

The premature termination of star formation process in some galaxies. The ultimate quenching of star formation is caused by stripping of the gas reservoir which will finally turn into stars. A wide variety of mechanisms have been proposed to provide quenching. For example, → major mergers can transform spiral galaxies into ellipticals, and may also quench future star formation by ejecting the → interstellar medium from the galaxy via starburst, → active galactic nucleus, or shock-driven winds. In rich clusters, where merging is less efficient because of the large relative velocities of galaxies, rapid encounters or fly-bys may cause the formation of a bar and growth of a spheroidal component instead of larger scale star formation. Also, cold gas can be stripped out of the galaxy both by tidal forces and ram pressure in the intracluster medium. Similarly, the hot halo that provides future fuel for cooling and star formation may be efficiently stripped in dense environments, thus quenching further star formation (see, e.g., Kimm et al., 2009, MNRAS 394, 1131, arXiv:0810.2794).

→ star; → formation; → quench.

The rate at which a molecular cloud or a galaxy is currently converting gas into stars. It is given by the ratio of the number of stars to the star formation time-scale.

→ star formation; → rate.

A region in the → interstellar medium where processes of → star formation are going on or have occurred in the past.

→ star; → formation; → region.

The time necessary for a star to form. It depends inversely on the stellar mass.

→ star formation; → time scale.

A → main sequence→ B-type star that orbits the → supermassive black hole candidate → Sgr A* in the → Galactic center. The star S2, which is bright enough for making detailed measurements, has a highly elliptical, 16-year-period orbit around Sgr A*. Near → pericenter at 120 → astronomical units, ~ 1400 → Schwarzschild radii, the star has an orbital speed of ~ 7650 km s^-1, such that the first-order effects of → special relativity and → general relativity have become detectable with current capabilities (Auber et al., 2018, A&A 615, L15).

→ star.

Same as → stellar system.

→ stellar; → system.

A curved → path left by a star on an → imaging detector attached to a → telescope when the telescope does not keep up with the → rotation of the → Earth.

→ star; → trail.

A galaxy that is located on the → galaxy main sequence in the plane relating → star formation rates to total stellar masses.

→ star; → formation; → galaxy.

A region in which → star formation is going on.

→ star; → formation; → region.

Simultaneous formation of a large number of stars in a region of a galaxy at an exceptionally high rate, compared to the usual star formation rates seen in most galaxies.

→ star; → burst.

A galaxy showing a short-lived intense period of star formation that is unsustainable over the → Hubble time due to the limited supply of gas within a galaxy. Starburst galaxies were first classified by Searle & Sargent (1972) and Searle et al. (1973), based on the blue colors produced by the → massive stars formed during the burst. In the local Universe, starbursts create approximately 10% of the radiant energy and 20% of the massive stars. At z = 1, starburst characteristics are found in 15% of galaxies, presumably attributable to the greater amounts of gas typically present in young galaxies and increased galactic interactions. The starburst's impact on a galaxy and the surrounding → intergalactic medium is primarily due to the consumption of gas that fuels the burst and the feedback from massive stars formed in the burst (McQuinn et al. 2010, astro-ph/1008.1589).

→ starburst; → galaxy.

The → splitting of spectral lines of atoms and molecules due to the presence of an external electric field, which slightly changes the → energy levels of the atom. → Zeeman effect.

Named after Johannes Stark (1874-1957), a German physicist, and Physics Nobel Prize laureate (1919); → effect.