An Etymological Dictionary of Astronomy and Astrophysics
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Same as the → Shapley supercluster.

→ Shapley's wing; → concentration

A rotation mode in which internal rotation of a star depends essentially on depth and little on latitude: Ω(r,θ) = Ω(r), where r is the mean distance to the stellar center of the considered level surface (or → isobar). This particular mode was introduced by J.-P. Zahn (1992, A&A 265, 115) to simplify the treatment of rotational → mixing, but also on more physical grounds. Indeed differential rotation tends to be smoothed out in latitude through → shear turbulence. See also → von Zeipel theorem; → meridional circulation .

Shellular, the structure of this term is not clear; it may be a combination of → shell (referring to star's assumed division in differentially rotating concentric shells) + (circ)ular, → circular. The first bibliographic occurrence of shellular is seemingly in Ghosal & Spiegel (1991, On the Thermonuclear Convection: I. Shellular Instability, Geophys. Astrophys. Fluid Dyn. 61, 161). However, surprisingly the term appears only in the title, and nowhere in the body of the article; → rotation.

Carxeš, → rotation; puste-yi, adj. of pusté, → shell.

The time taken by a planet or satellite to complete one revolution about its primary with respect to stars. For Earth, same as → sidereal year. Sidereal periods of the solar system planets, interms of the sidereal year, are as follows: Mercury 0.240846 (87.9691 days); Venus 0.615 (225 days); Earth 1 (365.25636 solar days); Mars 1.881; Jupiter 11.86; Satrurn 29.46; Uranus 84.01; and Neptune 164.8. That of the Moon is 0.0748 (27.32 days) and for → Sedna 12050.

→ sidereal; → revolution; → period.

The rotation period of a celestial body with respect to fixed stars. For Earth, same as → sidereal day.

→ sidereal; → rotation; → period.

1) Something that is signified, → meaning, sense.
2) The act of signifying. → significance, → significant, → level of significance.

Verbal noun of → signify.

1) A transformation that preserves angles and changes all distances in the same ratio.
2) A transformation of the form B = X^-1AX relating two → square matrices A and B.

→ similarity; → transformation.

A fraction in which the → numerator and → denominator are positive → integer numbers. Compare → compound fraction.

→ simple; → fraction.

The motion of a body subjected to a restraining force which is directly proportional to the displacement from a fixed point in the line of motion. The equation of simple harmonic motion is given by x = A sin(ωt + θ₀), where x is the body's displacement from equilibrium position, A is the → amplitude, or the magnitude of harmonic oscillations, ω is the → angular frequency, t is the time elapsed, and θ₀ is the → initial phase angle.

→ simple; → harmonic; → motion.

A set of stars resulting from a spatially (≤ few pc) and temporally (≤ Myr) correlated star formation event.

→ simple; → population.

The act of simplifying, or the fact of being simplified.

Verbal noun of → simplify.

The construction of a mathematical model to reproduce the characteristics of a phenomenon, system, or process, often using a computer, in order to infer information or solve problems.

Verbal noun of → simulate.

A radio astronomical observation which uses only one antenna, in contrast to interferometric observations.

→ single; → dish; → observation.

An atom that has lost one electron and has become a positive ion.

→ single; → ionized; → atom.

A carbon atom → singly ionized by a photon of energy 11.3 eV. The ion C⁺ emits a → fine-structure line (²P_3/2→ ²P_1/2) at 157.7 μm when excitation conditions are satisfied (critical density ~ 3 x 10³ cm^-3). In → photodissociation regions, [C II] 157.7 μm is a major cooling line for regions exposed to significant → far ultraviolet (FUV) photon fluxes. In Galactic → H II regions, as well as in the central regions of external galaxies, the luminosity of the [C II] line is typically ~ 0.05-0.5% of the FUV luminosity and correlates well with → carbon monoxide (CO) line intensities.

→ single; → ionized; → carbon.

Of partial differential equations, the solution which cannot be obtained from the general solution by particular choice of arbitrary functions. → general solution; → particular solution.

→ singular; → solution.

The process of choosing a site for an astronomical observatory based on meteorology, seeing conditions, and access to the site.

→ site; → selection.

1) The manner of being placed with respect to surroundings.
2) Momentary state; a set of circumstances.

Verbal noun of → situate.

The act or instance of removing the contribution of non-related, intervening foreground light to the object.

→ sky; → subtraction.

An asteroid taxonomy built on the → Tholen classification but based on the presence or absence of → absorption features in the visible part of the spectrum. In many cases the two classifications are the same, but the Tholen C and S classes are subdivided in the SMASS classification.

SMASS stands for the Small Main-belt Asteroid Spectroscopic Survey, → small; → main belt; → asteroid; → spectroscopic; → survey; → classification.

A method allowing for a simplified solution to the → radiative transfer equation at frequencies of spectral lines in media moving with a high velocity gradient. This method assumes that the macroscopic velocity gradients are more important than local random variations of thermal line width: dv/dr > v_th/l, where dv/dr is the velocity gradient, v_th is the thermal broadening of the line, and l the length scale. The Sobolev approximation is only valid if the conditions of the gas do not change over the → Sobolev length. Under the Sobolev approximation, each point in the medium is isolated from other points, and the → radiative transfer problem becomes a local one and therefore much easier to solve.

Named after the Russian astronomer Viktor Viktorovich Sobolev, Moving Envelopes of Stars [in Russian], Leningr. Gos. Univ., Leningrad (1947) [translated by S. Gaposchkin, Harvard Univ. Press, Cambridge, Mass. (1960)]; → approximation.