An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Variously colored → sedimentary rock composed mainly of sand-like quartz grains cemented by calcite, clay, or iron oxide. The sand accumulated originally underwater in shallow seas or lakes, or on the ground along shorelines or in desert regions.

→ sand; → stone.

A strong wind carrying sand through the air.

→ sand; → storm.

A deep → objective prism survey of the → Large Magellanic Cloud carried out with the Curtis Schmidt telescope on Cerro Tololo in Chile. A total of 1272 stars, generally brighter than → photographic magnitude ~ 14, are listed in the catalog as proven or probable LMC members. The stars are identified on the charts in the LMC Atlas of Hodge & Wright (1967).

By Nicholas Sanduleak (1933-1990), American astronomer, published in 1970 as Contribution No. 89 of the Cerro Tololo Inter-American Observatory; → catalog.

During the → main sequence stage, a star burns the hydrogen in its core and transforms it into helium. When the helium mass amounts to about 10% of the initial stellar mass, the star can no longer maintain the → hydrostatic equilibrium in its core; the star increases its volume and leaves the main sequence in order to become a → red giant.

Named after the Brazilian astrophysicist Mario Schönberg (1914-1990) and Subramahmanyan Chandrasekhar, → Chandrasekhar limit, who were the first to point out this limit and derive it (1942, ApJ 96, 161).

Faint wavy lines of alternating light and dark that sometimes can be seen on flat, light-colored surfaces just before and just after a total solar eclipse. The phenomenon results from sunlight distortion by irregularities in the Earth's atmosphere.

→ shadow; → band.

Either of the two bands of frequencies, one just above (upper side) and one just below (lower side) a carrier frequency, that result from modulation of a carrier wave.

→ side; → band.

Bând, → band; kenâr "side," variant karân "edge, limit;" Mid.Pers. karân, karânak, kenâr "edge, limit, boundary;" Av. karana- "side, boundary, end."

Same as → Alpheratz.

Sirah, contraction of Ar. As-Surrat al-Faras (السره‌الفرس) "The Horse's Navel," from surrat (سره) "navel" + faras (فرس) "horse." The name refers to the location of the star in the figure of → Pegasus. However, the star is now considered to belong to the constellation → Andromeda.

Ra's-ol-Mosalsalé, from Ar. Ar-Ra's al-Mar'ah al-Musalsalah "The head of the chained woman," from Ra's "head" + Mar'ah "woman" + Musalsalah "chained".

A criterion for → convective stability in → massive stars. The Solberg-Høiland stability criterion corresponds to the inclusion of the effect of → rotation (variation of → centrifugal force) in the convective stability criterion. It is a combination of → Ledoux's criterion (or possibly → Schwarzschild's criterion) and → Rayleigh's criterion. Both the dynamical shear and Solberg-Høiland instabilities occur in the case of a very large → angular velocity decrease outwards. Therefore, in a → rotating star the Ledoux or Schwarzschild criteria for convective instability should be replaced by the Solberg-Høiland criterion. More specifically, this criterion accounts for the difference of the centrifugal force for an adiabatically displaced fluid element. It is also known as the axisymmetric baroclinic instability. It arises when the net force (gravity + buoyancy + centrifugal force) applied to a fluid parcel in an adiabatical displacement has components only in the direction of the displacement (A. Maeder, Physics, Formation and Evolution of Rotating Stars, 2009, Springer).

E. Høiland, 1939, On the Interpretation and Application of the Circulation Theorems of V. Bjerknes. Archiv for mathematik og naturvidenskab. B. XLII. Nr. 5. Oslo.
H. Solberg, 1936 (reprint), Le mouvement d'inertie de l'atmosphere stable et son rôle dans la théorie des cyclones.
H. Solberg, 1941, On the Stability of the Circular Vortex. Avhandl. utg. av Det Norske Videnskaps-Akademi i Oslo. I. Mat-Naturv. Klasse. No. 11.
Wasiutynski, J. 1946, Astrophysica Norvegica, 4, 1.

To have or maintain an upright position, supported by one's feet; rise to one's feet (OxfordDictionaries.com).

M.E. standen, from O.En. standan "occupy a place; stand firm; stay, be, exist; oppose, resist attack; stand up, be on one's feet;" cognate with O.Norse standa, O.Saxon and Gothic standan, O.H.G. stantan, Du. staan, Ger. stehen, cognate with Pers. istâdan, as below.

Istâdan "to stand," from Mid.Pers. êstâtan; O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to stand."

Any set of conditions that describe the normal, desired, or ideal state of something, and that serves a basis for representing or evaluating actual examples of this thing.

M.E., from O.Fr. estandart "banner, standard," probably from Frankish *standord; cf. Ger. Standort "standing-point," from standan "to stand," cognate with Pers. istâdan, as below, with the second component conformed to -ard.

Estândé, literally "made stand, fixed," p.p. istândan transitive verb of istâdan, "to → stand."

A hypothetical vertical distribution of atmospheric temperature, pressure, and density that, by international agreement, is taken to be representative of the atmosphere for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and missile design, ballistic tables, etc.

→ standard; → atmosphere.

An astronomical object, belonging to some class, that has a known luminosity. In principle, by comparing the known luminosity to the observed brightness, the distance to the object can be derived. The four major primary distance indicators are Cepheids, supernovae, novae, and RR Lyrae variables. The secondary distance indicators include H II regions, globular clusters, brightest red and blue stars. → primary calibrator; → secondary calibrator.

→ standard; → candle.

The conventional → Big Bang model, which is based on two assumptions: the → cosmological principle of homogeneity and isotropy leading to the → Robertson-Walker metric, and → Einstein's field equations of general relativity along with familiar properties of matter. This model is a remarkably successful operating hypothesis describing the evolution of the Universe from 1/100 second after the initial event through to the present day. It provides explanations for several basic problems such as: → Hubble's law of recession of galaxies, interpreted in terms of the expansion of the Universe; the abundances of the → light elements, in excellent agreement with the predictions of → primordial nucleosynthesis; and the thermal spectrum and angular isotropy of the → cosmic microwave background (CMB) radiation, as expected from a hot, dense early phase of expansion. For a non-standard model, see → ekpyrotic Universe.

→ standard; → cosmology.

The most widely used measure of dispersion of a frequency distribution. It is equal to the positive square root of the → variance. Same as → standard error. Not to be confused with the → root mean square error.

→ standard; → deviation.

A particular date and time that specifies the reference system to which celestial coordinates are referred. From 1984 the → Julian year is used, as denoted by the prefix J, e.g. J2000.0.

→ standard; → epoch.

Same as → standard deviation.

→ standard; → error.

The accepted but possibly incomplete theoretical framework which usually describes a set of phenomena. For example, the model that describes the origin of the Universe, or the model concerned with the processes in the interior of the Sun.

→ standard; → model.

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.

Stars for which accurate color indices and/or magnitudes exist, defining a standard system.

→ standard; → star.

Photometric system used as a reference.

→ standard; → system.