An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1318
Sagittarius B2
  نیم‌اسب B2   
Nimasb B2

Fr.: Sagittarius B2   

A massive (3 × 106 → solar masses), dense (up to 108 particles per cm3) → H II region and → molecular cloud complex located near the → Galactic center (about 390 → light-years from it) and about 26,000 light-years from Earth. This complex is one of the largest in the → Milky Way, spanning a region about 150 light-years across. The mean → hydrogen  → density within the cloud is 3,000 atoms per cm3, which is about 20-40 times denser than a typical molecular cloud. It is the richest molecular source in the Galaxy in which many different types of → interstellar molecule have been identified, including glycine, the simplest amino acid, and the sugar molecule glycoaldehyde.


Sagittarius Dwarf Elliptical Galaxy
  کهکشان ِ کوتوله‌ی ِ بیضی‌گون ِ نیم‌اسب   
kahkešân-e kutule-ye beyzigun-e nimasb

Fr.: galaxie naine elliptique du Sagittaire   

A satellite galaxy of the Milky Way discovered only in 1994 since most of it is obscured by the Galactic disc. At only 50,000 light years distant from our Galaxy's core, it is travelling in a polar orbit around the Galaxy. Our Galaxy is slowly devouring it, as evidenced by a filament which stretches around the Milky Way's core like a gossamer loop. It is only about 10,000 light-years in diameter, in comparison to the Milky Way's diameter of 100,000 light years. It is populated by old yellowish stars has four known globular clusters: M54, Arp 2, Terzan 7, and Terzan 8. It should not be confused with the → Sagittarius Dwarf Irregular Galaxy.

Sagittarius; → dwarf; → elliptical; → galaxy.

Sagittarius Dwarf Irregular Galaxy
  کهکشان ِ کوتوله‌ی ِ بی‌سامان ِ نیم‌اسب   
kahkešân-e kutule-ye bisâmân-e Nimasb

Fr.: galaxie naine irrégulière du Sagittaire   

A dwarf irregular galaxy, discovered in 1977, that is a member of the Local Group of galaxies. It has a diameter of 1,500 light-years and lies about 3.5 million light-years away. SagDIG contains as much as about 108 solar masses of H I gas and is one of the most metal-poor galaxies. It should not be confused with the → Sagittarius Dwarf Elliptical Galaxy.

Sagittarius; → dwarf; → irregular; → galaxy.

Sagnac effect
  اسکر ِ سنیاک   
oskar-e Sagnac

Fr.: effet Sagnac   

The → phase difference between two light waves moving in opposite directions along a closed circular loop when the loop is rotating. More specifically, consider a beam of light split into two beams which are then allowed to propagate in two opposite directions along the rim of a rotating disk. When they are recombined, a phase difference occurs between them. The position of the → interference fringes is dependent on the → angular velocity of the setup. This → relativistic effect illustrates the impossibility of synchronizing clocks situated in a rotating → reference frame, as described by Einstein in 1905. The Sagnac effect is used, for example, in optical gyroscopes installed in airplanes or in devices used for measuring the Earth rotation. The Sagnac effect is very important for the correct working of the → Global Positioning System.

Named after Georges Sagnac (1869-1928), French physicist, who discovered the phenomenon in 1913; → effect.

Saha equation
  هموگش ِ ساها   
hamugeš-e Saha

Fr.: équation de Saha   

An equation that gives the number of atoms of a given species in various stages of → ionization that exist in a gas in → thermal equilibrium as a function of the temperature, density, and ionization energies of the atoms.

Named after the Indian astrophysicist Megh Nad Saha (1894-1956), who first derived the equation in 1920; → equation.

Saint Elmo's fire
  آتش ِ سپنت المو   
âtaš-e sepant Elmo

Fr.: feu de Saint-Elme   

A blue/violet light better seen at night on a pointed object, such as the mast of a ship or the wing of an airplane, during a → thunderstorm. The mast appears to be on fire but does not burn. It occurs when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The high voltage causes the electrons and protons of the air molecules to be pulled away from each other, transforming the air into a glowing ionized gas. St. Elmo's fire is sometimes mistaken for → ball lightning. It was identified as an electrical phenomenon first by by Benjamin Franklin in 1749. Also called → corposant.

Saint Elmo the Italian rendering of St. Erasmus of Formiae (died 303) the patron saint of Mediterranean sailors; → fire.

Âtaš, → fire, sepant "saint, holy," → heiligenschein.

Saiph (κ Orionis)
Seyf (#)

Fr.: Saiph   

A → supergiant star of visual magnitude 2.06 and → spectral type B0.5 Ia marking the right knee of Orion. It is about 700 light-years away.

Saiph "sword," from Ar. as-saiph al-jabbâr (سیف الجبار) "the Sword of the Giant."

Sakharov conditions
  بوتارهای ِ ساخاروف   
butârhâ-ye Sakharov

Fr.: conditions de Sakharov   

The three conditions that are necessary for the generation of a → baryon asymmetry in the → early Universe. These conditions are:
1) The → baryon number should not be → conserved.
2) The → charge conjugation and → CP symmetry should be → violated, and
3) Departure from → thermal equilibrium.

Named after Andrei Sakharov (1921-1989), who in 1967 described these three minimum conditions (A. D. Sakharov, 1967, Zh. Eksp. Teor. Fiz. Pis'ma 5, 32; 1967, JETP Lett. 91B, 24); → condition.

Sakurai's Object (V4334 Sgr)
  بر‌آخت ِ سکورایی   
barâxt-e Sakurai

Fr.: objet de Sakurai   

A → post-asymptotic giant branch star that in 1995 underwent sudden re-brightening due to a → helium shell flash, or → very late thermal pulse (VLTP), before embarking on a → white dwarf cooling track. Such an outburst is very rare, and in this case it is the first seen in modern times. Stellar outbursts observed in 1670 (nova CK Vul) and 1918 (nova V605 Aql) may have been caused by the same phenomenon. Since 1995, Sakurai's Object has undergone observable changes on time-scales of weeks to months. Several phases of dust production followed the outburst, with a deep optical minimum beginning in early 1999, such that any changes in the central star have since been inferred from radio and infrared observations. Subsequent observations and modeling have revealed much about the dust shell formation and the outer regions of the ejecta. This object is also the central star of an extended very faint planetary nebula (→ CSPN), confirming that the latest large mass ejection during the planetary nebula phase occurred several thousands years ago (see, e.g. H. L. Worters et al. 2009, MNRAS 393, 108 and references therein).

Named after Yukio Sakurai, a Japanese amateur astronomer, who serendipitously discovered it on February 20, 1996, when searching for comets; → object.

Salpeter function
  کریای ِ سلپیتر   
karyâ-ye Salpeter

Fr.: équation de Salpeter   

The first mathematical description of the → initial mass function (IMF) of newly formed stars of solar to → intermediate-masses. It is proportional to M -2.35, where M is the stellar mass. → Salpeter slope.

Named after the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter (1924-2008); → function.

Salpeter process
  فرارَوند ِ سلپتر   
farâravand-e Salpeter

Fr.: processus de Salpeter   

An equation describing how the nuclei of helium fuse together, in the interior of giant stars, to form carbon nuclei. → triple-alpha process.

Named after the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter (1924-2008); → process.

Salpeter slope
  شیب ِ سلپیتر   
šib-e Salpeter

Fr.: pente de Salpeter   

The value of the exponent in the → initial mass function as derived by Salpeter (1955) for solar to → intermediate mass stars in the Solar neighborhood: &Gamma = 1.35 or &alpha = 2.35, or x = -1.35. Also known as Sapleter index.

Salpeter function; → slope.

namak (#)

Fr.: sel   

1) A crystalline compound, sodium chloride, NaCl, occurring as a mineral, used for food seasoning and preservation.
2) Chem.: A solid compound formed when the hydrogen of an acid has been replaced by a metal.

O.E. sealt; cf. O.N., O.Fris., Goth. salt, Du. zout, Ger. Salz from PIE *sal- "salt;" cf. Gk. hals (genitive halos) "salt, sea;" L. sal; O.Ir. salann; Welsh halen; O.C.S. sali "salt."

Namak "salt;" Mid.Pers. namak "salt."

salt finger
  انگشت ِ نمک   
angošt-e namak

Fr.: doigts de sel   

Oceanography: One of several alternating columns of rising and descending water resulting from a → mixing process that occurs when warm salty water overlies a colder and relatively fresher layer of water. If the overlying salty water loses enough heat, it sinks down into the colder, fresher water, lengthening into a finger of salty water. Becuse the finger loses heat faster than it loses salt, the salt finger will continue to sink (salty water is denser than fresh water of the same temperature). Hence the salt finger loses more heat and displaces the colder water around it, which rises up and mixes into the warm salty layer above. Salt fingers are an example of → double-diffusive convection and play an important role in oceanic mixing. See also → fingering instability, → fingering convection.

salt; → finger.

šuré (#)

Fr.: salpètre   

A chemical compound, potassium nitrate, KNO3. It is a naturally occurring mineral source of nitrogen, and is used in the manufacture of fireworks, fluxes, gunpowder, etc.

M.E. sal peter, salpetre, from O.Fr. salpetre, from M.L. sal petrae "salt of rock," from L. sal, → salt + petra "rock, stone."

Šuré, related to šur "salty;" Mid.Pers. šôr "salty," šorag "salt land;" cf. Skt. ksurá- "razor, sharp knife;" Gk. ksuron "razor;" PIE base *kseu- "to rub, whet."


Fr.: échantillon   

Statistics: A portion of the units of a population. The units are selected based on a randomized process with a known probability of selection. The sample is used to make inferences about the population by examining or measuring the units in the sample. → specimen = nemuné (نمونه).

M.E., from O.Fr. essample, from L. exemplum "a sample," literally "that which is taken out," from eximere "to take out, remove."

Nemunân, from nemun, from nemudan "to show;" Mid.Pers. nimūdan, nimây- "to show," from O.Pers./Av. ni- "down; into," → ni- (PIE), + māy- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure."

sample point
  نقطه‌ی ِ نمونان   
noqte-ye nemunân

Fr.: point de l'échantillon   

Statistics: Each possible outcome in a → sample space.

sample; → point.

sample size
  اندازه‌ی ِ نمونان   
andâze-ye nemunân

Fr.: taille de l'échantillon   

The number of sampling units which are to be included in the sample. In the case of a multi-stage sample this number refers to the number of units at the final stage in the sampling.

sample; → size.

sample space
  فضای ِ نمونان   
fazâ-ye nemunân

Fr.: espace des échantillons   

Statistics: A set which consists of all possible outcomes of a random experiment.

sample; → space.


Fr.: échantillonnage   

The act, process, or technique of selecting a number of cases from all the cases in a particular population.

sample + → -ing.

Nemunân-giri, literally "taking sample," from nemunânsample + giri verbal noun of gereftan "to take, seize, hold;" Mid.Pers. griftan, gir- "to take, hold, restrain;" O.Pers./Av. 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 *ghrebh- "to seize."

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