An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 17 Search : sky
all-sky survey
  بردید ِ همه-آسمان   
bardid-e hame-âsmân

Fr.: relevé sur tout le ciel   

A → survey that collects data on the whole sky. For example the infrared → Two Micron All Sky Survey (2MASS) and the X-ray → ROSAT All-Sky Survey.

all; → sky; → survey.

blue sky
  آسمان ِ آبی   
âsmân-e âbi (#)

Fr.: ciel bleu   

A phenomenon which results from → Rayleigh scattering of sunlight by → atmospheric molecules. → Nitrogen and → oxygen molecules that compose about 78% and 21% of the air, respectively, are small compared to the light → wavelengths, and thus more effective at scattering shorter wavelengths of light (blue and violet). The → selective scattering by these → molecules is responsible for producing the blue skies on a clear sunny day. The sky over the horizon appears much paler in color, because the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Hence, less blue light reaches the observer's eyes.

blue; → sky.

Einstein-Podolsky-Rosen paradox
  پارادخش ِ اینشتین-پودولسکی-روزن   
pârâdaxš-e Einstein-Podolsky-Rosen

Fr.: paradoxe Einstein-Podolsky-Rosen   

EPR paradox.

A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Phys. Rev. 41, 777 (15 May 1935); → paradox.

fractional sky coverage
  پوشش ِ برخه‌ای ِ آسمان   
pušeš-e barxe-yi-ye âsmân

Fr.: couverture partielle du ciel   

The portion of the 4π → steradians of the sky that a radiotelescope can observe from a given location on Earth over a 24-hour time interval.

fractional; → sky; → coverage.

jansky (Jy)
jansky (#)

Fr.: jansky   

The unit of → radio flux density in → radio astronomy, equivalent to 10-26watts per square meter per → hertz.

Named in 1973 by the International Astronomical Union in honor of Karl Guthe Jansky (1905-1950), an American engineer of Czech descent who first identified radio waves from beyond the Solar System.

Palomar Observatory Sky Survey (POSS)
  بردید ِ آسمان ِ نپاهشگاه ِ پالومار   
bardid-e âsmân-e nepâhešgâh-e Palomar

Fr.: Palomar Observatory Sky Survey   

A photographic atlas of the northern hemisphere and a portion of the southern hemisphere created at Mount → Palomar Observatory in southern California. The original survey was completed in 1954 using the 48-in Schmidt (Oschin) Telescope. The square photographic plates were 35.5 cm (14-inch) on a side, each encompassing roughly 6 × 6 degrees of the sky. The survey was originally intended to cover the entire sky from +90 degrees declination down to -24 degrees (plate centers) in 879 regions, using both red and blue sensitive emulsions, and including stars to magnitude +22. Ultimately the survey was extended to -30 degrees (both red and blue), an additional 57 regions. Finally, the Whiteoak Southern Extension was added in 1962 (red plates only), with another 100 plates which extended the set down to a declination of -42 degrees plate center.

Palomar Observatory; → sky; → survey.

plane of the sky
  هامن ِ آسمان   
hâmon-e âsmân

Fr.: plan du ciel   

An imaginary plane that is perpendicular to the → line of sight.

plane; → sky.

âsmân (#)

Fr.: ciel   

The area high above the ground, buildings, landscape, or horizon.
The heavens or firmament, appearing as a great arch or vault.

M.E. from O.N. sky "cloud;" cf. O.E. sceo, O.S. scio "cloud;" O.H.G. scuwo, O.N. skuggi "shadow;" Goth. skuggwa "mirror;" PIE base *(s)keu- "to cover, conceal."

Âsmân "sky;" Mid.Pers. âsmân "sky, heaven;" O.Pers. asman- "heaven;" Av. asman- "stone, sling-stone; heaven;" cf. Skt. áśman- "stone, rock, thunderbolt;" Gk. akmon "heaven, meteor, anvil;" Akmon was the father of Ouranos (Uranus), god of sky; Lith. akmuo "stone;" Rus. kamen; PIE base *akmon- "stone, sky." The link between the "stone" and "sky" concepts indicates that the sky had once been conceived as a stone vault by prehistoric Indo-Europeans.

sky background
  پس‌زمینه‌ی ِ آسمان   
paszamine-ye âsmân

Fr.: fond du ciel   

The emission of a part of the night sky that does not contain any detectable objects. Sky background results from the combined radiation from faint, unresolved stars and other emitting astronomical objects. The mean brightness of night sky background measured at the → Cerro Tololo Inter-American Observatory (CTIO) for the period 1992 to 2006 are: U = 22.12, B = 22.82, V = 21.79, R = 21.19, and I = 19.85 mag arcsec-2 ( → rms ~ 0.2 mag arcsec-2). See also → sky brightness.

sky; → background..

sky brightness
  درخشندگی ِ آسمان   
deraxšandegi-ye âsmân

Fr.: brillance du ciel   

Atmospheric (→ airglow, → auroral emission, → artificial light) or extraterrestrial (→ scattered  → sunlight from Moon, scattered → starlight, → interplanetary dust) foreground light that → interferes with → observations.

sky; → brightness.

sky subtraction
  زیرکرشش ِ آسمان   
zirkaršeš-e âsmân

Fr.: soustraction de ciel   

The act or instance of removing the contribution of non-related, intervening foreground light to the object.

sky; → subtraction.

sky survey
  بردید ِ آسمان   
bardid-e âsmân

Fr.: relevé du ciel   

The observation and recording of large extents of the sky with a particular instrument using one or more wavelengths in the same spectral domain. → survey.

sky; → survey.

  نور ِ شهر، فروغ ِ آسمان   
nur-e šahr, foruq-e âsmân

Fr.: illumination du ciel   

The illumination of the night sky in urban areas caused by wasted light shining upward scattered off dust, humidity, and air. Skyglow is a type of → light pollution that results from light fixtures emitting a portion of their light directly upward into the sky. Light scattered in the atmosphere creates an orange-yellow glow above a city or town. Skyglow interferes with sensitive astronomical instruments designed to capture light from distant stars, nebulae, and galaxies. Skyglow can often be detected hundreds of kilometers away.

sky; → glow.

Nur, → light; foruq, → glow; šahr, → city; âsmân, → sky.

  نور ِ آسمان   
nur-e âsmân-e

Fr.: lumière du ciel   

Solar radiation which reaches the observer from the general sky. It is sunlight which has undergone multiple scattering events with the molecules of the Earth's atmosphere (Rayleigh scattering) or with clouds or other aerosols in the atmosphere. High levels of skylight reduce the contrast of a shadow. Also known as diffuse skylight, diffuse sky radiation.

sky; → light.

transient sky
  آسمان ِگذرا   
âsmân-e gozarâ

Fr.: ciel transitoire   

A general term for all events of astronomical nature occurring in the sky and lasting only for a relatively short duration, such as → supernova explosions, → gamma-ray bursts, → flare stars, → luminous red novae, eclipsing brown dwarfs, → tidal disruption events, etc.

transient; → sky.

Two Micron All Sky Survey (2MASS)

Fr.: 2MASS   

An astronomical → survey conducted from 1997 to 2001 of the entire sky in near-infrared J, H, and K bands (wavelengths 1.25, 1.65, and 2.17 microns respectively). The aim was to detect and characterize point sources brighter than about 1 → mJy in each band, with → signal-to-noise ratio greater than 10, using a pixel size of 2".0. Two automated 1.3-m telescopes were used, one at Mt. Hopkins, AZ, and one at CTIO, Chile. 2MASS is currently producing the following data products: 1) A digital atlas of the sky comprising approximately 4 million 8' × 16' images, having about 4" spatial resolution in each of the wavelength bands. 2) A point source catalog containing accurate positions and fluxes for 300 million stars and other unresolved objects. 3) An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and nebulae.

two; → micron; → all-sky survey.

Yarkovsky effect
  اُسکر ِ یارکوفسکی   
oskar-e Yarkovsky

Fr.: effet Yarkovski   

A phenomenon that causes a slow variation of the orbital elements of asteroids and meteoroids. It takes place because the surface thermal conductivity of these bodies is not negligible and the rotation of the body about its axis shifts the warmest region from midday to the object's afternoon hemisphere. Consequently the temperature distribution is asymmetric with respect to the Sun direction, and the momentum carried off by the photons emitted in the infrared has a net component along the orbital velocity of the asteroid. This causes a decrease or increase of its orbital energy depending on whether the rotation is prograde or retrograde. The bodies therefore spiral either sunward or outward. The secular drift of the semi-major axis of the orbit is estimated to be of the order of 10-4 A.U. per million years for a → near-Earth object with a diameter of 1 km. The effect is unimportant for bodies larger than a few km because of their very large mass per unit area (106 g cm-2 or more) and is especially unimportant for comets that spend little time under intense illumination close to the Sun. Compare with the → Poynting-Robertson effect, which is isotropic. See also → YORP effect.

Named after Ivan Osipovich Yarkovsky (1844-1902), a Russian-Polish civil engineer. Yarkovsky knew nothing of photons and based his reasoning on the → ether concept, but his idea survives the translation to modern physics; → effect.