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

A Galactic H II region with an electron density ≥ 10³ cm^-3 and of a linear dimension ≤ 1 pc.

→ compact; → H II region.

To examine in order to note similarities and differences.

From O.Fr. comparer, from L. comparare "to match, make equal with, liken," from → com- "with" + parare "to make or esteem equal," from par "equal."

Sanjidan "to compare; to measure," from Mid.Pers. sanjidan "to weigh," from present tense stem sanj-, Av. θanj- "to draw, pull;" Proto-Iranian *θanj-. Other terms from this base in Pers.: lanjidan "to pull up," hanjidan, âhanjidan "to draw out," farhang "education, culture."

A scenario for → massive star formation whereby developing → protostars in their natal → molecular clouds compete with each other to gather mass. The protostars → accrete mass with a rate which depends on their location within the protocluster. They use the same reservoir of gas to grow. Therefore those protostars nearest the center, where the potential well is deep, and gas densities are higher, have the highest → accretion rates. The competitive accretion model explains the observational fact that the most massive stars are generally found in cluster cores. It accounts also for the distribution of stellar masses. In this model the accretion process depends on the content of the cluster. In clusters where gas dominates the potential (e.g. at initial stages of cluster formation), the accretion process is better modeled by using the → tidal radius as the accretion radius. In contrast, when the stars dominate the cluster potential and are virialized, the accretion is better modeled by → Bondi-Hoyle accretion (Bonnell et al. 1997, MNRAS 285, 201; 2001, MNRAS 323, 785).

→ competitive; → accretion; → model.

Same as → complementary screens.

→ complementary; → aperture.

Two apertures where opaque and transparent areas are inverted. If A is an aperture that has some opaque areas and some transparent ones, the complementary pattern A' is the pattern in which exactly the opposite areas are opaque and transparent. Thus, the complimentary screen of a single slit is a wire of the same size, and the complementary screen of a circular opening is a dot. A better term would be → complementary apertures.

→ complementary; → screen.

1) Grasp mentally; understand.
2) Include, comprise, or encompass.
Comprehend and understand are very often interchangeable. In fact, both words mean "grasp the meaning of," but in some cases understand stresses the final result, while comprehend stresses the process of getting there.

From L. comprehendere "to take together, to unite; include; seize," from → com- "together, with," + prehendere "to seize," → prehend.

1) The ability to → comprehend something.
2) In logic, the sum of all the essential attributes which analysis can find in a concept or term. For example, the comprehension of the term man is rational animal; the → extension of the term man, is all men and women. Comprehension and extension are inversely proportional. The greater is the comprehension of a term, the less is its extension.

Verbal noun of → comprehend.

1) Completely or broadly covering; including a large proportion of something.
2) Having or showing extensive understanding.

From M.Fr. compréhensif, from L.L. comprehensivus, from L. comprehendere, → comprehend. comprehendo.

To press together; force into less space.

From O.Fr. compresser, from L. compressare "to press together," from comprimere "to squeeze," from → com- "together" + premere "to press;" PIE *prem-/*pres- "to strike."

Tanjidan "to squeeze, press, pull together," related to tang "tight," also "horse girth, a strap for fastening a load" (Mid.Pers. tang "tight, narrow"); cf. Skt. tanákti "draws together, contracts;" cognate with E. → tight; cp. Skt. tanákti "draws together, contracts;" M.H.G. dihte "dense, thick;" Ger. dicht "dense, tight;" O.H.G. gidigan; Ger. gediegen "genuine, solid, worthy;" PIE *tenk- "to thicken, clot; thick, solid."

Pressed into less space; condensed.

Past participle of → compress.

Air whose density is increased by being subjected to a pressure greater than atmospheric pressure.

→ compressed; → air.

The ability or quality to be reduced in volume. The coefficient of compressibility of a substance is given by c = (1/V).(δV/δp), where δV is the change in the volume resulting from a change of pressure δp, the temperature remaining constant.

Noun from → compressible.

Able to be reduced in volume. → compressible flow.

Adjective from → compress + -ible, variant of -able.

Tanjidani, tanješpazir from tanjidan, → compress, + adjective suffix -i; tanješpazir from tanješ, → compression, + pazir "receiving, admitting; having, endowed with;" → -able.

A flow in which changes of the density, induced by velocities and their fluctuations, are not negligible.

→ compressible; → flow.

The act or process of compressing; the state of being compressed.

Verbal noun from → compress.

In thermodynamics, the quantity Z = pV_m/RT, in which P is the gas pressure, V_m the molar volume, R the gas constant, and T the temperature. The compression factor is a measure of the deviation of a real gas from an ideal gas. For an ideal gas the compression factor is equal to 1.

→ compression; → facteur.

A → longitudinal wave that compresses the → medium along the direction of → propagation, such as a → sound wave. Same as → compressional wave.

→ compression; → wave.

Of or relating to → compression.

→ compression; → -al.

An → elastic wave that travels through a → medium with the particles of the medium moving in the same direction as the wave propagation. The compressional wave is the wave that is primarily used in → seismic exploration. Also called P-wave, primary wave, pressure wave.

→ compressional; → wave.

The change of direction undergone by the electron in the → Compton effect. The scattered photon and the collided electron move in different directions from that of the incident photon.

→ Compton; → recoil.