An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 214
Bâdbân (#)

Fr.: Voile   

The Sail. A part of the constellation Argo in the Southern hemisphere, which was later divided into three parts, the others being Carina and Puppis. Vela is situated at about 10h right ascension, -50° declination. Abbreviation: Vel; Genitive: Velorum.

From L. vela, plural of velum "sail, curtain, covering," velare "to cover, veil."

Bâdbân "sail," literally "wind keeper," from bâdwind + -bân a suffix denoting "keeper, guard," sometimes forming agent nouns or indicating relation, → host.

Vela pulsar
  پولسار ِ بادبان، تپار ِ ~   
pulsâr-e Bâdbân, tapâr-e ~

Fr.: pulsar du Voile   

A pulsar with a short period (89 milliseconds) associated with the → Vela supernova remnant. It is approximately 1500 light-years distant. The Vela pulsar is one of the few pulsars detectable optically. Its optical flashes, of visual magnitude 26, were detected in 1977. Also named PSR 0833-45.

Vela; → pulsar.

Vela supernova remnant
  بازمانده‌ی ِ اَبَر-نو‌اَختر ِ بادبان   
bâzmânde-ye abar-now-axtar-e Bâdbân

Fr.: reste de supernova du Voile   

A → supernova remnant located in the southern Milky Way in the constellation → Vela. It has a large angular diameter of about 8° and lies 250 ± 30 pc away (Cha et al. 1999, ApJ 515, L25). Its overall emission is dominated by the interaction of the → supernova blast wave with the → interstellar medium. This SNR is also notable for a number of protrusions extending well beyond its rim, which were suggested to be fragments of ejecta from the supernova explosion. X-ray spectroscopy has since confirmed several of these protrusions to indeed be strongly enriched with ejecta. The age of the SNR is estimated to be ~11,000 years, based on the spin-down rate of the associated → Vela pulsar, but ages as large as 20,000-30,000 years have also been argued.

Vela; → supernova remnant.

Vela X
  بادبان X   
Bâdbân X

Fr.: Vela X   

A compact radio source about 1500 light-years distant associated with the Vela supernova remnant. It has a nonthermal radio spectrum and is about 20 percent polarized. It is associated with the Gum Nebula, the Vela pulsar, and the X-ray source 2U 0832-45.

Vela; X for → X ray.


Fr.: vitesse   

The time rate of change of position in a given direction, measured as length per unit time. → speed.

L. velocitatem (nominative velocitas) "swiftness, speed," from velox (genitive velocis) "swift."

Tondâ, from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat") + noun suffix .

velocity curve
  خم ِ تندا   
xam-e tondâ

Fr.: courbe de vitesse   

A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines.

velocity; → curve.

velocity dispersion
  پاشش ِ تندا   
pâšeš-e tondâ

Fr.: dispersion de vitesses   

The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.

velocity; → dispersion.

velocity gradient
  زینه‌ی ِ تندا   
zine-ye tondâ

Fr.: gradient de vitesse   

Fluid Mechanics: The rate at which the velocity changes with the distance across the flow. When a fluid flows past a stationary wall, the fluid right close to the wall does not move. However, away from the wall the flow speed is not zero. Therefore a velocity gradient exists, which is due to adhesive, cohesive, and frictional forces. The amount of the velocity gradient is characteristic of the fluid.

velocity; → gradient.

velocity law
  قانون ِ تندا   
qânun-e tondâ

Fr.: loi de vitesse   

In the theory of → radiation-driven winds, an equation that describes the behavior of the → wind velocity of → hot stars as a function of distance from the star. This velocity β-law is given by the expression: v(r) = v(1 - R*/r)β, where v is the → terminal velocity, R* is the stellar radius, and r the distance from the center. For → O-type stars, the exponent is estimated to be β = 0.8.

velocity; → law.

velocity of light
  تندی ِ نور، تندای ِ ~   
tondi-ye nur, tondâ-ye ~

Fr.: vitesse de la lumière   

A → physical constant which represents the ultimate speed limit for anything moving through space, according to the theory of → special relativity. It is the speed of propagation of → electromagnetic waves in a vacuum, equal to 299,792.458 km/s (nearly 3 x 108 m/s). The velocity of light appears as the connecting link between mass and energy in the → mass-energy relation. Usually denoted by c, from L. celeritas "swiftness," from celer "swift," → acceleration.

velocity; → speed; → light.

velocity pressure
  فشار ِ توانیک   
fešâr-e tavânik

Fr.: pression dynamique   

dynamic pressure.

velocity; → pressure.

velocity profile
  فراپال ِ تندا   
farâpâl-e tondâ

Fr.: profil de vitesse   

A plot of the fluid velocity as a function of position.

velocity; → profile.

velocity space
  فضای ِ تندا، ~ تنداها   
fazâ-ye tondâyi, ~ tondâhâ

Fr.: espace de vitesses   

Of a dynamical system, a three-dimensional space which consists of the set of values that the velocity can take (vx, vy, vz). → phase space.

velocity; → space.

velocity-distance relation
  باز‌آنش ِ تندا-دورا   
bâzâneš-e tondâ-durâ

Fr.: relation vitesse-distance   

The linear relation wherein all galaxies are moving away from one another, with velocities that are greater with increasing distance of the galaxy. Same as → Hubble's law.

velocity; → distance; → relation.

vena contracta
  شاره‌گذر ِ ترنگیده   
šâre-gozar-e terengidé

Fr.: veine contractée   

The location in a → fluid stream where the → cross section of the → stream is at a minimum, and fluid velocity is the highest, such as in the case of a → jet issuing out of a → nozzle.

L. vena "channel;" contracta, "contracted," → contract.

Šâre-gozar "fluid passage," → fluid; → passage, terengidé, → contracted.

Venn diagram
  نمودار ِ وِن   
nemudâr-e Venn (#)

Fr.: diagramme de Venn   

A schematic diagram using circles to represent sets and the relationships between them. Each circle represents one set. Two or more may be overlapped. The areas of overlap indicate subsets.

Named after John Venn (1834-1923), a British logician and philosopher, who introduced the diagram; → diagram.

dudkaš (#)

Fr.: cheminée   

The subterranean conduit from the underlying → magma chamber through which a volcano ejects igneous material. Same as volcanic vent.

M.E. venten "to furnish (a vessel) with a vent," from O.Fr. esventer "to air," from es-, → ex-, + venter, from vent, from L. ventus "wind."

Dudkaš "chimney," literally "smoke extractor," from dud, → smoke, + kaš "to extract, to draw," present stem of kešidan/kašidan "to carry, draw, protract, trail, drag" (Mid.Pers. kešidan "to draw, pull;" Av. karš- "to draw; to plow," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base kwels- "to plow").

Venturi tube
  لوله‌ی ِ ونتوری   
lule-ye Venturi

Fr.: débitmètre de Venturi, tube de ~   

A → device used to → measure the → quantity of → fluid  → flowing through a → pipe.

Named after Italian physicist Giovanni Battista Venturi (1746-1822); → tube

Nâhid (#)

Fr.: Vénus   

The second → planet from the → Sun, at a mean distance of roughly 108.21 × 106 km (0.72 → astronomical units). Venus has the most circular orbit of any planet in the solar system. Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass). Its chemical composition and density are comparable to those of the Earth. It takes Venus just under 224.401 days to orbit the Sun, compared to the 365 day → orbital period of the Earth. Venus' rotation is → retrograde, that is it actually rotates from east to west, as opposed to west to east (→ prograde) which is the common rotating direction of most other planets. Seen from Venus, the sun would rise in the west and set in the east. Moreover, it takes about 244 Earth days for Venus to rotate once (→ sidereal rotation). This is longer than its orbital period. The length of its → solar day is about 117 Earth days. → Venus rotation. Its axial tilt is only three degrees, so there are no seasons on Venus. The → atmosphere on the surface of Venus consists mostly of → carbon dioxide, with a small trace of → nitrogen. Venus has a surface pressure about 90 times that of the Earth. → Venus visibility, → transit of Venus.

O.E., from L. Venus, the goddess of beauty and love in ancient Roman mythology, from venus "love, sexual desire, beauty, charm;" PIE base *wen- "to desire, love, wish;" cf. Av. vāunuš "lovingly," vantā- "beloved one, wife;" Skt. van- "to love, desire," vanánā- "desire," vanitā- "beloved one, wife;" O.H.G. wunsc(h) "wish," wunsken "to wish."

Nâhid, planet Venus, Mid.Pers. Anahid; O.Pers. anāhita- "immaculate, unstained," goddess of pure waters and fertility, from Av. arədvī-sūra-anāhita "valient and unsustained lord of waters," from arədvī- (Skt. Saravastī) probably "she who possesses water," + sūra- "strong, powerful" (Skt. śūra- "valiant, courageous") + anāhita- "unstained," from an- negation prefix + āhita "spotted."

Venus rotation
  چرخش ِ ناهید   
carxeš-e nâhid

Fr.: rotation de Vénus   

The → sidereal rotation period of Venus, or its → sidereal day, is 243.025 Earth days (retrograde). The length of a → solar day on Venus (that is one entire day-night period) is 116.75 Earth days, that is significantly shorter than the sidereal day because of the retrograde rotation. One Venusian year is about 1.92 Venusian solar days.

Venus; → rotation.

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