An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < abs act att clu com dif fac gal gal imp int opt qua ref str vul > >>

Number of Results: 307 Search : act
kahkešâni (#)

Fr.: galactique   

1) Of or pertaining to a → galaxy.
2) Usually with capital G, pertaining to our galaxy, the → Milky Way.

Adjective of → galaxy.

Galactic anticenter
  پادمرکز ِ کهکشان   
pâdmarkaz-e kahkešân

Fr.: anticentre galactique   

The point in the → Galactic plane that lies directly opposite the → Galactic center. It lies in the constellation → Auriga at approximately R.A. 05h 46m, Dec. +28° 56'.

galactic; → anticenter.

galactic bar
  میله‌ی ِ کهکشانی   
mile-ye kahkešâni

Fr.: barre galactique   

An elongated bar-shaped structure composed of stars present in some spiral galaxies. About two-third of such galaxies contain bars that cross their centers. Bars, like → spiral arms, result from a → density wave in which stars take very elliptical orbits. They form when the → galactic disk dominates the → galactic bulge, → Ostriker-Peebles criterion. Bars play an extremely important role in a galaxy's evolution. The gravity from a bar is the mechanism that drives → interstellar gas from the outer parts of a → spiral galaxy inward toward the central regions, and into the galactic nucleus itself. This causes tremendous bursts of star formation. Therefore, a majority of massive stars are born in such starbursts in the nuclei of galaxies. Bars may also channel the material that falls into black holes within active galactic nuclei, releasing enormous power in radiation and particles from tiny regions at the centers of some galaxies. Bars disappear as galactic centers grow more massive (after some 2 to 8 Gyr).

galactic; → bar.

Galactic bulge
  کوژ ِ کهکشان   
kuž-e kakhašân

Fr.: bulbe de la Galaxie   

The central → galaxy bulge of the → Milky Way.

galactic; → bulge.

Galactic Center
  مرکز ِ کهکشان   
markaz-e kahkešân (#)

Fr.: centre galactique   

1) The rotational center of the → Milky Way galaxy located in the direction of the → Sagittarius constellation at a distance of 7.62 ± 0.32 kpc (2005, ApJ 628, 246). Its equatorial coordinates (J2000 epoch) are: R.A. 17h45m40.04s, Dec. -29° 00' 28.1''. The Sun orbits around the Galactic center once every 200 million years at a speed of 220 km per second. It is believed that there is a → supermassive black hole at the Galactic center.
2) The innermost region of a → spiral galaxy characterized by high number of stars per unit volume. The center may contain a → supermassive black hole.

galactic; → center.

Galactic center cluster
  خوشه‌ی ِ مرکز ِ کهکشان   
xuše-ye markaz-e kahkešân

Fr.: amas du centre galactique   

One of the three massive clusters located toward the → Galactic center: → Quintuplet cluster, → Arches cluster, → Central cluster. Heavily extinguished by the presence of dust clouds and only accessible at infrared (and longer) wavelengths or in X-rays, each of these clusters has a population of more than a hundred → massive stars. The three clusters are similar in most respects, each containing about 104 solar masses in stars. The Arches cluster is younger than the two others.

galactic; → center; → cluster.

galactic cluster
  خوشه‌ی ِ کهکشانی، ~ کهکشانها   
xuše-ye kahkešâni, ~ kahkešânhâ

Fr.: amas galactique   

1) Same as → open cluster.
2) same as → cluster of galaxies.

galactic; → cluster.

Galactic coordinates
  هماراهای ِ کهکشانی   
hamârâhâ-ye kahkešâni

Fr.: coordonnées galactiques   

A system of astronomical coordinates using → latitude (bII) measured north and south from the → Galactic equator and → longitude (lII), measured from the → Galactic Center in the sense of increasing → right ascension from 0 to 360 degrees. In the old system (lI,bI), the Galactic center was at lI = 327°41'. Same as → galactic system.

galactic; → coordinate.

galactic disk
  گرده‌ی ِ کهکشان   
gerde-ye kahkešân

Fr.: disque galactique   

The flattened component of a → spiral galaxy which is composed of stars and concentrations of dust and molecules. → Star formation takes place mainly in the disk.

galactic; → disk.

galactic dynamics
  دینامیک ِ کهکشانی   
tavânik-e kakhešâni

Fr.: dynamique galactique   

The study of the → motions of the → stars, → gas, and → dark matter in a → galaxy to explain the main → morphological and → kinematical features of the galaxy.

galactic; → dynamics.

Galactic equator
  هموگار ِ کهکشان   
hamugâr-e kahkešân

Fr.: équateur galactique   

The great circle in the sky defined by the place of the → Galactic plane or the → Milky Way. At an angle of about 62°, the Galactic equator intersects the celestial equator at two points located in the constellations → Monoceros and → Aquila.

galactic; → equator.

Galactic habitable zone
  زنار ِ زیست‌پذیر ِ کهکشان   
zonâr-e zistpazir-e kahkešân

Fr.: zone habitable galactique   

A region of the Galaxy whose boundaries are set by its calm and safe environment and access to the chemical materials necessary for building terrestrial planets similar to the Earth. → circumstellar habitable zone; → habitable zone.

galactic, → habitable; → zone.

Galactic halo
  هاله‌ی ِ کهکشان   
hâle-ye kahkešân

Fr.: halo galactique   

A roughly spherical aggregation of → globular clusters, as well as the oldest stars and unseen mass that surrounds the Galaxy.

galactic, → halo.

Galactic latitude
  ورونای ِ کهکشانی   
varunâ-ye kahkešâni

Fr.: latitude galactique   

In the → Galactic coordinate system, the angle between the line of sight to an object and the → Galactic equator. Galactic latitude, usually represented by the symbol bII, ranges from +90 degrees to -90 degrees.

galactic; → latitude.

Galactic longitude
  درژنا‌ی ِ کهکشانی   
derežnâ-ye kahkešâni

Fr.: longitude galactique   

In the → Galactic coordinate system, the angle between the → Galactic Center and the projection of the object on the → Galactic plane. Galactic longitude, usually represented by the symbol lII, ranges from 0 degrees to 360 degrees.

galactic; → longitude.

galactic nucleus
  هسته‌ی ِ کهکشان   
haste-ye kahkešân

Fr.: noyau de galaxie   

A concentration of stars and gas in the innermost region of a galaxy, sometimes extending over thousands of light-years from the center of the galaxy.

galactic; → nucleus.

galactic outflow
  استچان ِ کهکشانی   
ostacân-e kahkešâni

Fr.: flot galactique   

galactic-scale outflow.

galactic; → outflow.

galactic plane
  هامن ِ کهکشان   
hâmon-e kahkešân

Fr.: plan galactique   

The plane in which the → disk of a → spiral galaxy, such as our → Milky Way, lies.

galactic; → plane.

galactic pole
  قطب ِ کهکشان   
qotb-e kahkešân

Fr.: pôle galactique   

The point on the sky, north or south, at which the galaxy's rotation axis would meet the celestial sphere.

galactic; → pole.

Galactic radio noise
  نوفه‌ی ِ رادیویی ِ کهکشان   
nufe-ye râdioi-ye kahkešân

Fr.: bruit radio de la Galaxie   

A diffuse radio signal that originates outside the solar system. It is strongest in the direction of the Galactic plane.

galactic; → radio; → noise.

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