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

1) To provide or obtain → insurance on or for.
2) Make certain that something is definitely so. Same as make sure and ensure.

Variant of → ensure.

1) Bimé kardan, from bimé, → insurance, + kardan "to do, make," → -ize.
2) Dartenzidan, from dar-, → in-, + tenz, → sure, + -idan infinitive suffix, → -ize.

The pressure exerted by a magnetic field on the material that contains the field.

→ magnetic; → pressure.

1) A unit or standard of → measurement; the act or process of ascertaining the extent, dimensions, or quantity of something; measurement; the quantity obtained by such a process.
2) To use standard units to determine the magnitude, extent, size, etc. of something. The quantity obtained by such a process.

From O.Fr. mesurer, from L.L. mensurare "to measure," from L. mensura "a measuring, a thing to measure by," from mensus, p.p. of metiri "to measure," → meter.

1) Andâzé "measure," from Mid.Pers. andâzag, handâcak "measure," handâxtan, handâz- "to measure," Manichean Mid.Pers. hnds- "to measure," Proto-Iranian *hamdas-, from ham-, → com-, + *das- "to heap, amass;" cf. Ossetic dasun/dast "to heap up;" Arm. loanword dasel "to arrange (a crowd, people)," das "order, arrangement."
2) Andâzé gereftan, compound verb, literally "to take measure," from andâzé, as above, + gereftan "to take, seize" (Mid.Pers. griftan; Av./O.Pers. grab- "to take, seize;" cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab;" from P.Gmc. *grab; E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

1) The act of measuring; a measured quantity.
2) The determination of the magnitude or amount of a quantity by comparison (direct or indirect) with the prototype standards of the system of units employed (IEEE Standard Dictionary of Electrical and Electronics Terms). → absolute measurement, → measurement uncertainty, → Roemer's measurement.

Verbal noun of → measure.

The interval within which lies the actually measured value of a physical quantity and the true value of the same physical quantity.

→ measurement; uncertainty, from negation prefix un- + → certainty.

The division of a relatively long exposure into several successive shorter ones, e.g. to avoid detector saturation.

→ multiple; → exposure.

A kind of pressure that contrarily to ordinary pressure pushes inward. In contrast with the → Newtonian mechanics, in → general relativity there are situations in which pressure can be negative. Positive pressure gives rise to attractive gravity, whereas negative pressure creates → repulsive gravity.

→ negative; → pressure.

The hydrostatic pressure produced on the surface of a partially permeable membrane by osmosis.

→ osmotic; → pressure.

Excessive exposure of a detector, → over-expose.

→ over-; → exposure.

1) The state or feeling of being pleased.
2) Enjoyment or satisfaction derived from what is to one's liking; gratification; delight.
3) Worldly or frivolous enjoyment (Dictionary.com).

M.E., from O.Fr. plesir, plaisir "enjoyment, delight, desire," from plaisir "to please," from L. placere "to please, give pleasure."

Zusé, from Av. zuš- "to take pleasure;" related to O.Pers. daušta- "friend," Mid.Pers. dôš- "to love, like, choose," dôšišn "pleasure, liking;" Parthian zwš "love;" Mod.Pers. dôst, dust "friend;" cf. Skt. jos- "to like, enjoy;" Gk. geuomai "to taste;" L. gusto "I taste;" gustus "taste, enjoyment."

The force per unit area.

M.E., from O.Fr. pressure, from L. pressura "action of pressing," from pressus, p.p. of premere "to press, compress."

Fešâr "squeezing, constriction, compression," verb fešordan, fešârdan "to press, squeeze;" phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- "to exhilarate;" loaned in Arm. ôšarak, in Ar. afšaraj "juice."

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star's atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

→ pressure; → broadening.

The pressure difference between two adjacent regions of a fluid that results in a force being exerted from the high pressure region toward the low pressure region.

→ pressure; → gradient.

A force resulting from → pressure gradient that is directed from high to low pressure.

→ pressure; → gradient; → force.

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

→ pressure; → ionization.

Same as → p mode

→ pressure; → mode.

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: H_P = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

→ pressure; → scale; → height.

The → momentum carried by → photons to a surface exposed to → electromagnetic radiation. Stellar radiation pressure on big and massive objects is insignificant, but it has considerable effects on → gas and → dust particles. Radiation pressure is particularly important for → massive stars. See, for example, → Eddington limit, → radiation-driven wind , and → radiation-driven implosion. The → solar radiation pressure is also at the origin of various physical phenomena, e.g. → gas tails in → comets and → Poynting-Robertson effect.

→ radiation; → pressure.

The pressure exerted on a body moving through a → fluid medium. For example, a → meteor traveling through the Earth's atmosphere produces a → shock wave generated by the extremely rapid → compression of air in front of the → meteoroid. It is primarily this ram pressure (rather than → friction) that heats the air which in turn heats the meteoroid as it flows around the meteoroid. The ram pressure increases with → velocity according to the relation P = (1/2)ρv², where ρ is the density of the medium and v the relative velocity between the body and the medium. Similarly, → ram pressure stripping produces → jellyfish galaxies. Same as → dynamic pressure.

→ ram; → pressure.

A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 10⁷ K) and tenuous (~ 10^-4 cm^-3) gas (several 10¹³ → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).

→ ram; → pressure; → strip.