An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 707
rišé (#)

Fr.: racine   

1) Math.: A quantity that, when multiplied by itself a certain number of times, produces a given quantity. For example, since 3 × 3 × 3 × 3 = 81, 3 is a fourth root of 81.
2) Math.: A solution to an equation f(x) = 0. We say that x0 is a root or zero of a → polynomial if f(x0) = 0. For example, the roots of the equation x2 - 9 = 0 are +3 and -3.
3) In → graph theory, a special → vertex that turns a → tree into a → rooted tree or a graph into a → rooted graph.

From M.E., from O.E. rot, from O.N. rot "root;" cf. O.H.G. wurz "plant, herb;" Ger. Wurz; cognate with L. radix, radius "staff;" Gk. rhiza "root;" Albanian rrânzë "root;" PIE base *u(e)rad- "twig, root."

Rišé "root" (dialectal Tabari rexa; Kurd. regez, riše), from Mid.Pers. rêšak "root," maybe ultimately related to PIE *u(e)rad-, as above, although the Skt. offshoot is absent.

root mean square (rms)
  ریشه‌ی ِ چاروشی ِ میانگین، ~ ِ دوم ِ ~   
riše-ye câruši-ye miyângin, ~ dovom-e ~

Fr.: valeur quadratique moyenne   

The square root of the arithmetic mean of the squares of the numbers in a given set.

root; → mean; → square.

root-mean-square error
  ایرنگ ِ ریشه‌ی ِ چاروشی ِ میانگین، ~ ~ ِ دوم ِ ~   
irang-e riše-ye câruši-ye miyângin, ~ ~ dovom-e ~


The square root of the second moment corresponding to the frequency function of a random variable.

root; → mean; → square; → error.

root-mean-square value
  ارزش ِ ریشه‌ی ِ چاروشی ِ میانگین   
arzeš-e riše-ye câruši-ye miyângin

Fr.: écart quadratique moyen, écart type   

Statistics: The square root of the arithmetic mean of the squares of the deviation of observed values from their arithmetic mean.

root; → mean; → square; → deviation.

rooted graph
  نگاره‌ی ِ ریشه‌دار   
negâre-ye rišedâr

Fr.: graphe raciné   

In → graph theory, a → graph that has one of its → vertices, called the → root, distinguished from the others.

root; → graph.

rooted tree
  درخت ِ ریشه‌دار   
deraxt-e rišedâr

Fr.: arbre raciné   

In → graph theory, a → tree in which one → vertex is distinguished from the other vertices and is called the root.

root; → tree.


Fr.: ROSAT   

A German X-ray satellite developed through a cooperative program with the United States and the United Kingdom. The satellite, launched by a Delta rocket (Cape Canaveral) on June 1, 1990, operated until February 12, 1999. ROSAT consisted of two telescopes performing in the → soft X-ray (0.1-2.4 keV) and → extreme ultraviolet (EUV) (006-0.2 keV) ranges. It carried out the first → all-sky surveys with imaging X-ray and EUV telescopes leading to the discovery of 125,000 X-ray and 479 EUV sources. In addition the diffuse Galactic X-ray emission was mapped with unprecedented angular resolution (≤ 1 arcmin). Most of the mission time was devoted to pointed observations at selected targets. ROSAT imaged everything from nearby asteroids and comets to distant quasars during its 8-year mission. The main ROSAT data centers were and are at the Max Planck Institute for Extraterrestrial Physics in Garching (X-rays) and at the University of Leicester (EUV) with mirror sites at the Goddard Space Flight Center and other research institutes.

ROSAT, short for the → ROentgen SATellite, in honor of the German physicist.


Fr.: Rosetta   

A spacecraft launched in March 2004 by the → European Space Agency to be the first man-made object to orbit a → comet's → nucleus. Rosetta will also be the first spacecraft to fly alongside a comet as it heads toward → perihelion in the inner → solar system. After a ten-year voyage across the solar system, it will reach a → periodic comet known as Comet 67P/ → Churyumov-Gerasimenko. Rosetta will remain in close proximity to the icy nucleus as it plunges toward the warmer inner reaches of the Sun's realm. Rosetta orbiter's scientific payload includes 11 different instruments, in addition to a robotic lander and 10 solar panels spanning 32 m tip to tip. In November 2014, Rosetta will launch the 100 kg lander, named Philae, onto the comet. Philae will touch down and then fire a harpoon to anchor itself and prevent it from escaping the comet's weak gravity. The lander carries 10 instruments, including a drill to take samples of subsurface material. More than a year will pass before the remarkable mission comes to an end in December 2015. By then, both the spacecraft and the comet will have circled the Sun and will be on their way out of the inner solar system. Rosetta's prime objective is to help understand the origin and evolution of the solar system. The comet's composition reflects the composition of the pre-solar nebula out of which the Sun and the planets of the solar system formed, more than 4.6 billion years ago. Therefore, an in-depth analysis of comet 67P/Churyumov-Gerasimenko by Rosetta and its lander will provide essential information to understand how the solar system formed. Before arriving at 67P/Churyumov-Gerasimenk, Rosetta flew by the → asteroids 2867 → Steins and 21 → Lutetia in 2008 and 2010, respectively, and gathered data on them.

Named for the Rosetta Stone, a black stele that was inscribed with a royal decree (196 BC) in two languages using three scripts: Egyptian hieroglyphics, Egyptian Demotic, and Greek. The Rosetta Stone was found in a small village in the Nile Delta called Rashid (Rosetta) in 1799. The spacecraft's robotic lander is called Philae, after a similarly inscribed obelisk found on an island in the Nile River. Both the stone and the obelisk were key to deciphering ancient Egyptian hieroglyphs, carried out by Jean-François Champollion (1790-1832) in 1822. Astronomers hope the Rosetta mission will provide a key to many questions about the origins of the solar system.

Rosette Nebula
  میغ ِ گلسان   
miq-e golsân

Fr.: nébuleuse de la Rosette   

A giant H II region of about 1° in diameter, lying about 5000 light-years away in the Milky Way, the constellation → Monoceros. It is ionized by the cluster NGC 2244, a group of hot young stars at the center of the nebula. Also called M16, the brighter portions of the nebula have been assigned different NGC numbers: 2237, 2238, 2239, and 2246.

Rosette "a rose-shaped ornament," from Fr. rosette, from O.Fr. rosette, diminutive of rose "rose;" L. rosa, probably from Gk. wrodon (Aeolic), then rhodon, a loan from Iranian, as below; → nebula.

Miq, → nebula; golsân "resembling rose, flower," from gol "flower, rose," variants vard (sohre-vard "red rose"), Semnâni dialect vela "rose;" Mid.Pers. *vard, gul, loaned in Arm. vard and Ar. ward; Av. varəδa- "rose;" loaned in Gk. wrodon (Aeolic), then rhodon; + -sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career").

Rossby number
  عدد ِ رسبی   
'adad-e Rossby

Fr.: nombre de Rossby   

A dimensionless number relating the ratio of inertial to Coriolis forces for a given flow of a rotating fluid. It is used in the study of atmospheric motions in planets. In case a small number is involved, cyclones and anticyclones are observed for low and high pressures. When it is large (Venus) the Coriolis force becomes negligible and atmospheric motions are barely affected by planetary rotation.

Named after Carl-Gustav Arvid Rossby (1898-1957), a Swedish-American meteorologist who first explained the large-scale motions of the atmosphere in terms of fluid mechanics; → number.

Rossby parameter
  پارامون ِ روسبی   
pârâmun-e Rossby

Fr.: paramètre de Rossby   

The northward variation of the Coriolis parameter, arising from the sphericity of the Earth.

Rossby number; → parameter.

Rossby wave
  موج ِ روسبی   
mowj-e Rossby

Fr.: onde de Rossby   

A wave on a uniform current in a two-dimensional non-divergent fluid system, rotating with varying angular speed about the local vertical.

Rossby number; → wave.

Rosseland mean opacity
  کدری ِ میانگین ِ روسلاند   
kederi-ye miyângin-e Rosseland

Fr.: opacité moyenne de Rosseland   

The → opacity of a gas of given composition, temperature, and density averaged over the various wavelengths of the radiation being absorbed and scattered. The radiation is assumed to be in → thermal equilibrium with the gas, and hence have a → blackbody spectrum. Since → monochromatic opacity in stellar plasma has a complex frequency dependence, the Rosseland mean opacity facilitates the analysis. Denoted κR, it is defined by: 1/κR = (π/4σT3) ∫(1/kν) (∂B/∂T)νdν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and kν monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507).

Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity.

Rossiter-McLaughlin effect
  اُسکر ِ راسیتر-مک‌لاکلین   
oskar-e Rossiter-McLaughlin

Fr.: effet Rossiter-McLaughlin   

A → spectroscopic phenomenon observed when either an → eclipsing binary's → secondary star or an → extrasolar planet is seen to → transit across the face of the → primary body. Because of the rotation of the star, an asymmetric distortion takes place in the → line profiles of the stellar spectrum, which changes during the transit. The measurement of this effect can be used to derive the → alignment of the → orbit of the transiting exoplanet with respect to the → rotation axis of the star.

Named after Richard Alfred Rossiter (1886-1977) and Dean Benjamin McLaughlin (1901-1965), American astronomers.

carxidan (#)

Fr.: tourner   

To turn around an axis. See also → revolve.

From L. rotare "to cause to spin, roll, move in a circle," from L. rota "wheel;" cognate with Pers. râh "way, path" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE *roto- "to run, to turn, to roll").

Carxidan "to rotate," from carx "every thing performing a circulatory motion; a wheel; a cart;" Mid.Pers. chr "wheel," Parthian cxr "wheel;" Ossetic calx "wheel;" Av. caxra- "wheel;" cognate with Skt. cakra- "wheel, circle; cycle," carati "he moves, wanders;" Gk. kyklos "circle, wheel," polos "axis of a sphere," polein "move around;" L. colere "to dwell in, to cultivate, move around," colonus "farmer, settler;" O.E. hweol "wheel;" Rus. koleso "wheel."

  چرخنده، چرخان   
carxandé, carxân

Fr.: en rotation   

Capable of or having rotation.

From → rotate + → -ing.

rotating black hole
  سیه‌چال ِ چرخان   
siyahcâl-e carxân

Fr.: trou noir en rotation   

A black hole that possesses angular momentum, as first postulated by Roy C. Kerr in 1963. Opposite of a stationary black hole. → ergosphere.

rotating; → black hole.

rotating star
  ستاره‌ی ِ چرخان، ~ چرخنده   
setâre-ye carxân, ~ carxandé

Fr.: étoile en rotation   

A star that has a non-zero → angular velocity. In a rotating star, the → centrifugal forces reduce the → effective gravity according to the latitude and also introduce deviations from sphericity. In a rotating star, the equations of stellar structure need to be modified. The usual spherical coordinates must be replaced by new coordinates characterizing the → equipotentials. See also → von Zeipel theorem.

rotating; → star.

carxeš (#)

Fr.: rotation   

The motion of a body about its axis.

Verbal noun of → rotate.

rotation axis
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation.

rotation; → axis.

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