An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

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Number of Results: 12960 Search : far
cylindrical
  استوانه‌ای   
ostovâne-yi (#)

Fr.: cylindrique   

Of, pertaining to, or having the form of a cylinder.

From L. cylindricus, from Gk. kylindrikos, see → cylinder; → -ic; → -al.

cylindrical coordinates
  هماراهای ِ استوانه‌ای   
hamârâhâ-ye ostovâne-yi (#)

Fr.: coordonnées cylindriques   

A coordinate system for a point in space, using an origin (O) and three perpendicular axes (Ox, Oy, Oz), in which a point (P) in space is specified by three numbers ρ, φ, z. The two first numbers, ρ and φ, are → polar coordinates for the vertical projection of P on the xy-plane, and z is the vertical distance of P from the xy-plane.

cylindrical; → coordinate.

cylindrical lens
  عدسی ِ استوانه‌ای   
adasi-ye ostovâneyi (#)

Fr.: lentille cylindrique   

A lens in which at least one surface is formed like a portion of a cylinder. Also called astigmatic lens.

cylinder; → lens.

Cynthian
  ماهی، مانگی   
mâhi (#), mângi (#)

Fr.: cynthien   

Referring to the Moon.

From L. Cynthia "the Moon," from Gk. Kynthia "woman from Kynthos." Kynthos was the mountain on Delos on which she and her twin brother Apollo were born.

Mâhi, mângi referring to mâh, mâng, → moon.

Cytherean
  ناهیدی   
Nâhidi (#)

Fr.: cythérien   

Referring to the planet Venus.

From Cythera, in Gk. mythology another name of Aphrodite (Roman equivalent Venus), goddess of love and beauty, since she was believed to emerge from the Mediterranean island Cythera.

Nâhidi referring to Nâhid, planet Venus, Mid.Pers. Anahid "immaculate, unstained," goddess of pure waters and fertility, from Av. arədvi-sûra-anâhita, from arədvi- "increasing, rising," + sûra- "strong, powerful" (Skt. śūra- "valient, courageous") + anâhita "unstained," from an- negation prefix + âhita "spotted."

D line
  خط ِ D   
xatt-e D

Fr.: raie D   

One of the pair of yellow lines in emission spectra of neutral sodium (Na I). D1 has a wavelength of 5895.94 Å and D2 is 5889.97 Å. This sodium doublet is one of the strongest absorption features in the spectra of late-type stars.

Labelled D in a sequence of alphabetical letters first used by Joseph von Fraunhofer to designate spectral features in the solar spectrum, → Fraunhofer line.

D ring
  حلقه‌ی ِ D   
halqe-ye D

Fr.: anneau D   

The inner → Saturn's rings, with a width of 7,500 km, lying before the → C ring, at 66,900 km from the center of Saturn.

ring.

d'Alembert's paradox
  پارادخش ِ دالامبر   
pârâdaxš-e d'Alembert

Fr.: paradoxe de d'Alembert   

A hydrodynamical paradox arising from the neglect of → viscosity in the → steady flow of a fluid around a submerged solid body. According to this paradox, the submerged body would offer no resistance to the flow of an → inviscid fluid and the pressure on the surface of the body would be symmetrically distributed about the body. This paradox may be traced to the neglect of the viscous forces, which are indirectly responsible for fluid resistance by modifying the velocity field close to a solid body (Meteorology Glossary, American Meteorological Society).

d'Alembert's principle; → paradox.

d'Alembert's principle
  پروز ِ دالامبر   
parvaz-e d'Alembert

Fr.: principe de d'Alembert   

The statement that a moving body can be brought to a → static equilibrium by applying an imaginary inertia force of the same magnitude as that of the accelerating force but in the opposite direction. More specifically, when a body of mass m is moving with a uniform acceleration a under the action of an external force F, we can write: F = m . a, according to Newton's second law. This equation can also be written as: F - ma = 0. Therefore, by applying the force -ma, the body will be considered in equilibrium as the sum of all forces acting on it is zero. Such equilibrium is called → dynamic equilibrium. Owing to this principle, dynamical problems can be treated as if they were statical.

Named after the French mathematician and philosopher Jean le Rond d'Alembert (1717-1783), who introduced the principle in his Traité de dynamique (1743).

d'Alembert-Lagrange principle
  پروز ِ دالامبر-لاگرانژ   
parvaz-e d'Alembert-Lagrange

Fr.: principe d'Alembert-Lagrange   

d'Alembert's principle.

d'Alembert's principle; → Lagrangian.

d'Alembertian operator
  آپارگر ِ دالامبر   
âpârgar-e d'Alembert

Fr.: d'alembertien   

A second order, → partial differential operator in space-time, defined as: ▫2 = ∂2/∂x2 + ∂2/∂y2 + ∂2/∂z2 - (1/c2)∂2/∂t2, or ▫2 = ∇2 - (1/c2)(∂2/∂t2), where ∇2 is the → Laplacian and c is the → speed of light. This operator is the square of the → four-dimensional operator  ▫, which is Lorentz invariant.

d'Alembert's principle; → operator.

D-type ionization front
  پیشان ِ یونش ِ گونه‌ی ِ D   
pišân-e yoneš-e gune-ye D

Fr.: front d'ionisation de type D   

An → ionization front of → H II regions whose expansion speed is comparable to the → sound speed in the gas (~ 10 km/sec for hydrogen at 104 K). A D-type ionization front results from → R-type ionization front when its propagation speed decreases as the volume of gas ahead of the ionization front grows. If front velocity is equal to a lower limit (C12 / 2C2, where C1 and C2 are the sound speed ahead and behind the front respectively), the front is called D critical.

D referring to a dense gas; → type; → ionization; → front.

D3 line
  خط ِ D3   
xatt-e D3

Fr.: raie D3   

The → neutral → helium  → spectral line at 5876 Å.

D3, because of confusion with the sodium → D lines. When Joseph N. Lockyer first observed this line in the solar spectrum at the eclipse of 1868, helium was not yet isolated on Earth. Initially, this line was thought to be the third member of the D1 and D2 line family of sodium which lie in the same yellow part of the spectrum; → line.

DA white dwarf
  سفید‌کوتوله‌ی ِ DA   
sefid kutule-ye DA

Fr.: naine blanche DA   

A → white dwarf whose spectrum shows the → Balmer lines of hydrogen only, with no helium or metals.

D short for → dwarf; A a convention; → white.

Dalton minimum
  کمینه‌ی ِ دالتون   
kamine-ye Dalton

Fr.: minimum de Dalton   

A 40-year period of unusually low → solar activity, from about 1790 to 1830. See also the → Maunder minimum.

Named after John Dalton (1766-1844), British meteorologist; → minimum.

damping
  میرایی   
mirâyi (#)

Fr.: amortissement   

Of an oscillating system, the progressive decrease with time in the amplitude of the oscillation, due to friction (internal or external) or other resistance.

M.E. damp "black damp, a poison gas occurring in a mine," from Mid.Du. or Mid. Low German; akin to O.H.G. damph "vapor."

Mirâyi, noun from mirâ "getting extinguished, going out, expiring, dying," from mordan, present tense stem mir- "to die," Mid.Pers. murdan "to die," O.Pers. mrt- "to die," amriyta "dies," martiya- "(mortal) man" (Mod.Pers. mard "man"), Av. mərəta- "died," Skt. mar- "to die," mrti- "death;" PIE base *mor-/*mr- "to die." Cognates in other IE languages: Gk. emorten "died," ambrotos "immortal," L. morior "I die," mortuus "dead" (Fr. mourir "to die," mort "dead"), Arm. merani- "to die," O.C.S. mrutvu "dead," O.Ir. marb, Welsh marw "died," O.E. morþ "murder," Lith. mirtis "man."

dance
  ۱) وشت؛ ۲) وشتن، وشتیدن   
1) vašt (#); 2) vaštan (#), vaštidan

Fr.: 1) danse; 2) danser   

1a) A successive group of rhythmical steps or bodily motions, or both, usually executed to music.
1b) An act or round of dancing.
2a) To move one's feet or body, or both, rhythmically in a pattern of steps, especially to the accompaniment of music.
2b) To leap, skip, etc., as from excitement or emotion; move nimbly or quickly (Dictionary.com).

M.E. da(u)ncen "to dance," from O.Fr. dancier of unknown origin, perhaps related to O.H.G. *dansjan "to lead (someone) to a dance."

Vašt, variant of gašt, gardidan, gel, gelidan "to turn," → revolve, cf. Eastern Gilâni gilâr "dance."

dancer
  وشتار، وشتنده، وشتگر   
vaštâr, vaštande, vaštgar

Fr.: danseur, danseuse   

1) A person who dances.
2) A person who dances professionally, as on the stage (Dictionary.com).

dance; → -er.

Vaštâr, from vašt "dnace," + agent noun suffix -âr, as in parastâr, padidâr; vaštande, vaštgar with agent noun suffixes, -ande and -gar, → -or.

danger
  خطر   
xatar (#)

Fr.: danger   

1) Liability or exposure to harm or injury; risk; peril.
2) An instance or cause of peril; menace (Dictionary.com).

M.E. daunger, from O.Fr. dangier "power, power to harm, authority, control," alteration of dongier, from V.L. *dominarium "power of a lord," from L. dominus "lord, master," → domain.

Xatar "danger," loan from Ar.

Danjon astrolabe
  اسطرلاب ِ دانژون   
ostorlab-e Danjon

Fr.: astrolabe de Danjon   

A modern unportable astrolabe which is used for high precision measuring of stellar and geographical coordinates. The instrument uses the simultaneous observations of two images of the same star, one of the images formed directly by the lower face of a prism and the other by the light rays reflected first from a mercury bath and then by the upper face of the prism. The images coincide when the zenithal distance of the star attains a prefixed value (Gauss method of equal altitudes, → almucantar). Apart from astrometry, the Danjon astrolabe was used for studying the Earth's rotation and is currently used for solar radius measurements.

After André Danjon (1890-1967), French astronomer, who developed the instrument at the Strasbourg Observatory before the Second World War and at the Paris Observatory in 1948. The concept of prism astrolabe was initially invented by the French Auguste Claude (1858-1938) around 1900 and was later modified in collaboration with Ludovic Driencourt (1861-1940); → astrolabe.

<< < -es -iv -ti 21- A r abe abs abs acc acc acc act act ada adi adu aff age alc Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app aps arc Arg ari art ass ast ast ast atm ato att aur aut axi B r bac Bal Bar Bar Bay bec Ber Bet Bie bij bin bio bis bla bla blu blu bol Bor bou Bra bre bro Bug C-s cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che cho cir cir cir cla clo clo clu co- cod coh col col col com com com com com com com com com con con con con con con con con con con con coo cop cor cor Cor cos cos Cou cou Cra Cre cri cro cub cur cya cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dog Dop dou dra dua dus dwa dyn E-E Ear ech eco edu eig Ein ela ele ele ele ele elo emi emp ene eni ent epi equ equ erg est Euc eva evo exa exc exe exo exp exp ext ext F r fac fam fas fee Fer Fib fig fin fir fix fle flu foc For for for fov fre fre Fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo gig glo gov gra gra gra gra gre gro Gum Hab hal han har Hay hea hel hel hem Her het hig Hil hol hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp inc inc ind ind inf inf inf inf inj ins ins int int int int int int int int inv Io ion iro isl iso iso Jal JHK Jul jur Kel Kep kin kne L2 Lag lam Lap lar lat law Lec len Lep lib lig lin lin lin liq lit loc log lon los low lum lun lux Lyr mac mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil min mir mix mod mol mom Moo mos Mu mul mus nad nas nat neb neg net neu New New nig Noe non non non Nor nuc nuc nul nut obe obl obs occ oct off Olb one ope opp opt opt orb orb org Ori ort oth out Owl P-s pal par par par par Pas pat pej peo per per per per per pha Phe pho pho pho phy pin pla pla pla pla pla plu poi pol pol Pol pol pos pos pot pra pre pre pre pre pri pri pro pro pro pro pro pro pro pse pul Pup Qua qua qua qua que rac rad rad rad rad rad rad ran rap ray rea rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot rur Sac sal sat sca sca Sch sci Scu sec sec Sed sel sem sen Ser Sey Sha she sho sid sig sim sin sip ske sli smo soc sol sol sol sol sol sou spa spa spe spe spe spe sph spi spo Squ sta sta sta sta ste ste ste sto str str str sub sub sub sum sup sup sup sup sur sus sym syn T d tap tec tem ten tes the the the the thi thr tid tim tip ton tor tow tra tra tra tra tri tri tru tub tur two Typ ult un- und uni uni unp upp urg V20 Van var veg vel ver vib vio vir vis vol vul war wat wav WC5 wea Wer whi WIM wis WO wor X-r yie Zan Zet > >>