An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 40 Search : cloud
intergalactic cloud
  ابر ِ اندرکهکشانی   
abr-e andarkahkešâni

Fr.: nuage intergalactique   

Intergalactic matter in the form of clouds.

intergalactic; → cloud.

interstellar cloud
  ابر ِ اندر‌اختری   
abr-e andaraxtari

Fr.: nuage interstellaire   

An aggregation of gas and dust in the → interstellar medium containing large quantities of atoms, molecules, and dust. There are several types of interstellar clouds, such as → diffuse interstellar clouds, → dark clouds, → molecular clouds.

diffuse; → cloud.

Large Magellanic Cloud (LMC)
  ابر ِ بزرگ ِ ماژلان   
Abr-e Bozorg-e Magellan (#)

Fr.: Grand Nuage de Magellan   

The larger of the two Magellanic Cloud galaxies visible in the southern hemisphere at about 22 degrees from the South Celestial Pole. It is approximately on the border between the constellations → Dorado and → Mensa in a region of faint stars. The center of the LMC is approximately RA: 5h 23m 35s, dec: -69° 45' 22''. The LMC shines with a total → apparent visual magnitude of approximately zero. It spans an area of the sky about 9 by 11 degrees, corresponding to about 30,000 → light-years across in the longest dimension, for a distance of some 162,000 light-years. It has a visible mass of about one-tenth that of our own Galaxy (1010 Msun). The LMC and its twin, the → Small Magellanic Cloud, are two of our most prominent Galactic neighbors. The LMC is classified as a disrupted → barred spiral galaxy of type SBm, the prototype of a class of → Magellanic spirals. The galaxy is characterized by a prominent offset → stellar bar located near its center with the dominant → spiral arm to the north with two "embryonic" arms situated to the south. The → metallicity in the LMC is known to be lower than in the solar neighborhood by a factor 2 or more. Based on 20 → eclipsing binary systems, the distance to the LMC is measured to one percent precision to be 49.59±0.09 (statistical) ±0.54 (systematic) kpc (Pietrzynski et al., 2019, Nature 567, 200).

large; → Magellanic; → cloud.

local interstellar cloud
  ابر ِ اندر-اختری ِ محلی   
abr-e andar-axtari-ye mahali

Fr.: nuage interstellaire local   

An → interstellar cloud that surrounds the → heliosphere.

local; → interstellar; → cloud.

Lupus dark cloud
  ابر ِ تاریک ِ گرگ   
abr-e târik-e Gorg

Fr.: nuage sombre du Loup   

Any of the several → dark clouds lying in the direction of the constellation → Lupus between → Galactic longitudes 334° < l < 352° and → Galactic latitudes +5° < b < +25°. In terms of angular extent the whole group is one of the largest low-mass star forming complexes on the sky, and it also contains one of the richest associations of → T Tauri stars. An average distance of about 150 pc places it among the nearest star forming regions, together with those in Corona Australis, Ophiuchus, Taurus-Auriga, and Chamaeleon (Comeron, 2008, in Handbook of Star Forming Regions Vol. II, PASP, Reipurth, ed.).

Lupus; → dark; → cloud.

Magellanic Clouds
  ابرهای ِ ماژلان   
Abrhâ-ye Magellan

Fr.: Nuage de Magellan   

Two irregular satellite galaxies of our own Galaxy which are visible from the Southern Hemisphere as misty patches in the night sky. → Large Magellanic Cloud; → Small Magellanic Cloud.

Magellanic; → cloud.

magnetic cloud
  ابر ِ مغناتیسی   
abr-e meqnâtisi

Fr.: nuage magnétique   

A transient ejection in the → solar wind having an enhanced field, a large and smooth change in field direction, and a low → proton temperature compared to the ambient proton temperature (L. F. Burlaga, 1995, Interplanetary Magnetohydrodynamics, Oxford Univ. Press, 89-114).

magnetic; → cloud.

molecular cloud
  ابر ِ مولکولی   
abr-e molekuli (#)

Fr.: nuage moléculaire   

A relatively dense, cold region of interstellar matter where the atoms are primarily bound together as molecules rather than free atoms or ionized particles. Molecular clouds represent the coldest and densest phase of the → interstellar medium. They consist primarily of → molecular hydrogen (H2), with temperatures in the range 10-100 K. Molecular hydrogen is not directly observable under most conditions in molecular clouds. Therefore, almost all current knowledge about the properties of molecular clouds has been deduced from observations of molecules such as → carbon monoxide (CO), which have strong emission lines mainly in the → millimeter portion of the → electromagnetic spectrum. So far 129 molecular species have been detected in molecular clouds, among which complex organic molecules. → Dust grains in molecular clouds play a crucial role in the formation of molecules. Molecular clouds are the principal sites where stars form. → giant molecular cloud; → Orion molecular cloud.

molecular; → cloud.

noctilucent cloud
  ابر ِ شب‌تاب   
abr-e šabtâb

Fr.: nuage nocturne lumineux   

The highest clouds in the Earth's atmosphere, at altitudes between 75 and 90 km. They resemble thin cirrus clouds with a bluish or silverish color, and are visible only during twilight.

From nocti- combining form of L. nox, → night, + L. lucent p.p. of lucere "to shine," from luxlight; → cloud.

Abr, → cloud, + šabtâb "noctilucent," from šab, → night, + tâb present stem of tâbidan "to shine," → luminous.

Oort cloud
  ابرِ اورت   
abr-e Ort (#)

Fr.: nuage de Oort   

A huge theoretical cloud of → comets surrounding the Sun between about 50,000 and 100,000 → astronomical units and thought to be the reservoir of → long-period comets entering the inner solar system.

Named after Jan Hendrik Oort (1900-1992), a Dutch astronomer who proposed its existence in 1950. He also made major contributions to our knowledge of the structure and rotation of the Milky Way Galaxy; → cloud.

Orion molecular cloud
  ابرِ مولکولی ِ شکارگر، ~ ~ ا ُریون   
abr-e molekuli-ye Šekârgar, ~ ~ Orion

Fr.: nuage moléculaire d'Orion   

A giant cloud, or complex of clouds, of interstellar gas and dust associated with the Orion nebula (M42). It is about 1,500 light-years away and measures about 240 light-years across. Besides M42 and M43 it contains a number of famous objects, including Barnard's Loop, the Horsehead Nebula, and the reflection nebulae around M78. Within this cloud, stars have formed recently, and are still in the process of formation.

Orion; → molecular cloud.

parent cloud
  ابر ِ پرمار   
abr-e permâr

Fr.: nuage parent   

Usually of a newborn star, the molecular cloud in which the star has formed.

parent; → cloud.

passive cloud
  ابر ِ اکار   
abr-e akâr

Fr.: nuage passif   

A cumulus cloud that is no longer dynamically connected with the atmospheric boundary layer via updrafts or downdrafts.

passive; → cloud.

rain cloud

Fr.: nuage de pluie   

Any cloud from which rain falls.

rain; → cloud.

Zafâk "rain cloud" (Dehxodâ); Mid.Pers. zafâ.

Rho Ophiuchi Cloud
  ابر ِ رو-مارافسا   
abr-e rho Mâr-afsâ

Fr.: Nuage de rho Ophiuchi   

A complex region of molecular and dust clouds containing emission and reflection nebulae near the star ρ Oph in the constellation → Ophiuchus. It is one of the closest star forming regions, some 400 light-years distant. Recent studies using the latest X-ray and infrared observations reveal more than 300 young stellar objects within the large central cloud. Their median age is only 300,000 years.

Rho, Gk. letter; → Ophiuchus; → cloud.

roll cloud
  ابر ِ لوله‌وار   
abr-e lule-vâr

Fr.: nuage en rouleau   

A low, horizontal, tube-shaped, and relatively rare type of → arcus cloud.

M.E. scroll, inscribed scroll, register, cylindrical object < OF ro(u)lle M.E. rolle, from O.Fr. roule, rolle, from M.L. rotulus "a roll of paper," from L. rotula "small wheel," diminutive of rota "wheel;" → cloud.

Abr, → cloud; lule-vâr "tube like," from lulé "tube, pipe," related to lulidan "to roll, rotate; to stir, vibrate" + -vâr suffix of resemblance.

Small Magellanic Cloud (SMC)
  ابر ِ کوچک ِ ماژلان   
Abr-e Kucak-e Magellan (#)

Fr.: Petit Nuage de Magellan   

An irregular galaxy, the smaller of the two → Magellanic Clouds that are satellites of our own Galaxy, lying in the southern constellation → Tucana about 20 degrees from the → south celestial pole. The SMC covers an area roughly 3 by 5 degrees in dimension and has an overall → visual magnitude about +2.7. The SMC is about 10,000 → light-years in diameter and some 210,000 light-years (61 → kpc) away. It has a visible mass of about 1/50-th that of our Galaxy and 1/10-th of that of the → Large Magellanic Cloud (LMC). Its → heavy element content is about a factor 5 smaller than that of the Galaxy. The SMC is the third-nearest external galaxy after the → Sagittarius Dwarf Elliptical Galaxy and the LMC.

small; → Magellanic; → cloud.

Smith's cloud
  ابر ِ اسمیت   
abr-e Smith

Fr.: nuage de Smith   

A huge, → high-velocity cloud of hydrogen gas that measures some 9,800 × 3,300 → light-years. It is located between 36,000 and 45,000 light-years away from Earth in the northern constellation of → Aquila. It has a mass of at least 106 → solar masses. It is now moving toward the disk of the → Milky Way at 73 ± 26 km/s and is expected to hit the disk of our Galaxy in about 27 million years, at an angle of approximately 45° at a point in the → Perseus Arm, one of two major → spiral arms of the Galaxy.

Named after Gail Bieger, née Smith, who discovered the cloud in 1963, when she was an astronomy student at Leiden University in the Netherlands; → cloud.

translucent cloud
  ابر ِ تراتاب   
abr-e tarâtâb

Fr.: nuage translucide   

A type of → interstellar medium cloud where → carbon (C), in → ionized atomic form and protected from → interstellar radiation, transforms into neutral atomic or molecular form. The chemistry in this regime is qualitatively different than in the → diffuse molecular clouds, both because of the decreasing electron fraction and because of the abundance of the highly reactive C atoms. The translucent cloud regime is the least well understood of all the cloud types. This is partly because of a relative lack of observational data, but also because theoretical models do not all agree on the chemical behavior in this transition region. In some models, there is a zone where the abundance of C exceeds that of C+ and CO; in others the peak abundance of C falls below that of C+ and CO. To cope with this uncertainty, Snow & McCall (2006) propose a working definition of translucent cloud material as gas with C+ fraction < 0.5 and CO fraction < 0.9. This definition reflects the fact that C+ is no longer the dominant form of carbon as it converts to neutral or molecular form, but also excludes the → dense molecular clouds, where carbon is almost exclusively CO (Snow & McCall, 2006, ARA&A 44, 367).

translucent; → cloud.

warm intercloud medium
  مدیم ِ اندر-ابری ِ گرم   
madim-e andarabri-ye garm

Fr.: milieu internuage chaud   

A component of the → interstellar medium consisting of an extremely tenuous (density 0.1 to 10 cm-3) and relatively warm gas (temperature about 8,000 K) filling the space between denser neutral and ionized gas. Hydrogen is partly ionized, partly atomic and observed by the → 21-centimeter line in emission.

warm; → intercloud medium.

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