An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -gr alp ast atm Bon con ear exo gra hom Jos Mod Oph pha Phe pho pho pho phy pul sid sph sta the > >>

Number of Results: 474 Search : pH
Bonnor-Ebert sphere
  سپهر ِ بونور-ابرت، کره‌ی ِ ~   
epehr-e Bonnor-Ebert, kore-ye ~

Fr.: sphère de Bonnor-Ebert   

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

Bonnor-Ebert mass; → sphere.

broad-band photometry
  شیدسنجی ِ پهن-باند   
šidsanji-ye pahn-bând

Fr.: photométrie à bande large   

Photometric measurements carried out through filters with a band-width (about one-tenth the central wavelength) in the range 30-100 nm. Typical examples are Johnson photometry, Krons-Cousins RI photometry, and the six-color system.

broad; → band; → photometry.

bump Cepheid
  کِفِیءوسی ِ قوزدار، ~ زوکدار   
Kefeusi-ye quzâr, ~ zokdâr

Fr.: céphéide à bosse   

A subtype of classical → Cepheid variable stars that show a bump on the descending branch of their → light curve.

Bump "a relatively abrupt convexity or bulge on a surface," probably imitative of the sound of a blow; → Cepheid.

Quzdâr, from quz "hump," variant of kuž, → convex, + -dâr "possessing," from dâštan "to have, possess." Zokdâr, from Lori zok "a raised spot, a bulge," cf. Northern Fârs Âbâdé dialect lok " swellimg, knob;" Kefeusi, → Cepheid.

burning sphere
  گوی ِ سوزان   
guy-e suzân

Fr.: sphère ardente   

A piece of glass of roundish shape, possibly made of rock crystals or a globular container filled with water, whose use is attested in ancient civilizations. In his comedy The Clouds, the Greek playwright Aristophanes (448-380 BC) mentions globules of glass that were known as burning spheres. Several Roman writers (Pliny, Seneca, Plutarch) speak of burning glasses. In particular, Seneca specifies that small and indistinct written characters appear larger and clearer when viewed through a globular glass filled with water. See also → magnifying glass.

burning; → sphere.

Guy, → globe; suzân "burning," → burning.


Fr.: catastrophe   

A great, often sudden calamity; a complete failure; a sudden violent change in the earth's surface. → cataclysm.

From Gk. katastrophe "an overturning, ruin," from katastrephein "to overturn, ruin" from kata "down" + strephein "to turn."

Negunzâr, from negun "overturned, inverted" + -zâr suffix denoting profusion, abundance, as in kârzâr "a field of battle; combat" šurezâr "unfertile, salty ground; nitrous earth," xoškzâr "arid land," and so forth.


Fr.: catastrophisme   

The doctrine that certain vast geological changes in the Earth's history were caused by sudden, short-lived, violent events rather than gradual evolutionary processes. Catastrophism explains the differences in → fossil forms encountered in successive → stratigraphic levels. This doctrine is associated with the French naturalist Baron Georges Cuvier (1769-1832). Catastrohism is contrasted to the → uniformitarianism.

catastrophe; → -ism.

celestial sphere
  سپهر ِ آسمانی، کره‌ی ِ ~   
sepehr-e âsmân (#), kore-ye ~ (#)

Fr.: sphère céleste   

An imaginary sphere, of large but indefinite dimension, used as a basis to define the position coordinates of celestial bodies. The center can be the Earth, the observer, or any other point which plays the role of origin for a given system of coordinates. Seen from the Earth, the celestial sphere rotates around the → celestial axis every 23h 56m 04s (the → sidereal day), as a result of the Earth's rotation. Two important circles on the celestial sphere are the → celestial equator and the → ecliptic. The angle between them, about 23.40 degrees, is known as the → obliquity of the ecliptic. The celestial equator and the ecliptic intersect at two points, → vernal equinox and → autumnal equinox. The positions of the → celestial poles and therefore that of the → celestial equator move gradually on the celestial sphere, due to → precession.

celestial; → sphere.


Fr.: céphéide   

A class of luminous, → yellow supergiants that are pulsating variables and whose period of variation is a function of their → luminosity. These stars expand and contract at extremely regular periods, in the range 1-50 days. Their highest brightness and surface temperature occur when their expansion velocity is greatest. Similarly, their minima in brightness and temperature occur when they are in the contraction phase. The longer the period, the more luminous the star. The process that drives the pulsation of → Cepheid variables is the → kappa mechanism. In fact, Cepheids provide one of the most powerful tools for measuring distances to other galaxies (→ period-luminosity relation). However, this method is limited to the distance of the → Virgo cluster of galaxies (15-20 → Mpc) even with the → HST or the largest ground-based telescopes. One particularly special Cepheid is the North Star, → Polaris. See also → RR Lyrae star.

Named after the prototype → Delta Cephei discovered by John Goodricke in 1784. → Cepheus.

Cepheid variable
  ورتنده‌ی ِ کفیءوسی   
vartande-ye Kefeusi

Fr.: variable Céphée   

A → variable star belonging to the class of → Cepheids.

Cepheid; → variable.


Fr.: Céphée   

A → constellation in the Northern Hemisphere lying next to → Cassiopeia. It contains several pulsating variable stars, including the prototype → Cepheid variable Delta Cephei. Abbreviation: Cep, genitive: Cephei.

In Gk. mythology, Cepheus, king of Ethiopia, who was married to the beautiful → Cassiopeia, and was also father of princess → Andromeda.

Kefeus, from Gk. Cepheus. Arabicizd form qifâvus (قیفاووس).

  خالکودوست، مسدوست   
xâlkdust, mesdust

Fr.: élémznt chalcophilz   

chalcophile element.

chalco-; → -phile.

chalcophile element
  بن‌پار ِ خالکودوست، ~ مسدوست   
bonpâr-e xâlkdust, ~ mesdust

Fr.: élément chalcophile   

In the → Goldschmidt classification, a → chemical element that has an → affinity for sulphur, and therefore tending to be more abundant in sulphide minerals and ores than in other types of rock. This group is depleted in the silicate Earth and may be concentrated in the core. The group includes → silver (Ag), → arsenic (As), → bismuth (Bi), → cadmium (Cd), → copper (Cu), → mercury (Hg), → indium (In), → lead (Pb), → sulfur (S), → antimony (Sb), → selenium (Se), → tellurium (Te), and → thallium (Tl). As a consequence of their relatively low condensation temperatures (500-1100 K), most of these elements are depleted in terrestrial planets with respect to chondrites.

chalcophile; → element.

  فام‌سپهر، رنگین‌سپهر   
fâmsepehr (#), ranginsepehr (#)

Fr.: chromosphère   

A region of the stellar atmosphere situated above its → photosphere. The Sun's chromosphere extends from the about 500 km above the photosphere basis, up to 9,000 km, where it meets the → corona. For a plane-parallel model, the chromosphere is more or less continuous throughout the first 1,500 km, but breaks into indented spicules beyond that height. The chromosphere temperature grows from 4,400 K at 500 km to almost 6,000 K at 1,000-2,000 km. A rapid growth of coronal temperatures is registered at heights of about 2,500 km (the transition region), the exact height depending on the local magnetic field intensity. Actually, the chromosphere is made of rising and, often, falling jets called → spicules, which go up to 15,000 km. In the uppermost part of the chromosphere the density is the millionth part of its density at the base. Immediately before or after a solar → total eclipse, the chromosphere becomes visible either as a crescent or as a red → diamond ring, due to → H-alpha emission, from which it also gets its name. Moreover, the chromosphere can be seen in → H and K lines of calcium during eclipses, and in ultraviolet emission lines from space. The presence of the chromosphere around cold → dwarf stars is deduced from similar emissions (M.S.: SDE).

chromo- "color," because of the reddish-pink color of the chromosphere which is seen around the Sun during a total eclipse and is due to the dominance of the → H-alpha line; → sphere.


Fr.: chronographe   

A very accurate instrument that measures, indicates, or graphically records time intervals such as the duration of an event.

Chronograph, from Gk. khronos "time" + → -graph.

Gâhnegâr, from gâh "time" + negâr, → -graph.

circumscribed sphere
  سپهر ِ پیراوشته، کره‌ی ِ ~، گوی ِ ~   
sepehr-e pirâvešte, kore-ye ~, guy-e ~

Fr.: sphère circonscrite   

A sphere containing a polyhedron (such as a pyramid) all of whose vertices lie on the surface of the sphere. The polyhedron so contained is said to be inscribed in the sphere.

Circumscribed p.p. of → circumscribe; → sphere.

classical physics
  فیزیک ِ کلاسیک   
fizik-e kelâsik (#)

Fr.: physique classique   

Physics not taking into account → quantum mechanics or Einstein's → relativity theory. Classical physics includes the branches developed before the beginning of the 20th cantury: Mechanics, Acoustics, Optics, Thermodynamics, and Electricity and Magnetism. Most of classical physics is concerned with matter and energy on the normal scale of observation.

classical; → physics.

closure phase
  فاز ِ بندش   
fâz-e bandeš

Fr.: clôture de phase   

In astronomical interferometry, a method using triplets of telescopes in an array to calculate the phase information and get over the effects of atmospheric turbulence. The method, used in high-resolution astronomical observations, both at radio and at optical wavelengths, allows imaging of complex objects in the presence of severe aberrations.

closure; → phase.

cometary atmosphere
  جو ِ دنباله‌دار، هواسپهر ِ ~   
javv-e donbâledâr, havâsepehr-e ~

Fr.: atmosphère de comète   

The envelope of → gas and → dust around a → comet nucleus, also known as → coma. As the comet approaches the → Sun, the frozen materials → sublimate and give rise to an expanding atmosphere. The atmosphere is composed of dust, → molecules, → radicals, and molecular → ions released from the inner coma with velocities ~ 0.5 to 1 km s-1, well above the → escape velocity for the nucleus. The → chemical species observed in cometary spectra can be divided into several categories: (i) atoms and molecules related to → water (H, O, OH, OH+, H2O, H2O+), (ii) carbon and related molecules (C, C+, CO, CO+, CO2+, C2, CH, CH+, HCO, H2CO), (iii) → nitrogen and related molecules (CN, CN+, HCN, CH3CN, NH, NH2, N2+, NH3, NH4), (iv) → sulphur and related molecules (S, CS, S2, H2S+), (v) → metals (Na, K, Ca, Co, Cr, Cu, V, Fe, Mn, Ni). For a typical average comet the neutral atmosphere is first seen when the heliocentric distance is d ≤ 3 → astronomical units.

cometary; → atmosphere.

complete graph
  نگاره‌ی ِ اسپر   
negâre-ye ospor

Fr.: graphe complet   

In → graph theory, a simple graph with an → edge between every pair of → vertices.

complete; → graph.

Compton catastrophe
  نگونزار ِ کامپتون   
negunzâr-e Compton

Fr.: catastrophe de Compton   

In a compact, steady radio-source where the density of relativistic electrons and the density of synchrotron radiation due to these electrons are very large, the radio photons should be transformed into X-ray and gamma-ray photons through inelastic Compton scatterings onto the relativistic electrons. Thus the radio photons should rapidly disappear and only gamma-ray photons should be observed. This phenomenon does not take place if the radio source is in relativistic expansion.

Compton; → catastrophe.

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