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

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13176 Search : in
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.

Danjon scale
  مرپل ِ دانژون   
marpel-e danjon

Fr.: échelle de Danjon   

A scale to evaluate as exactly as possible the darkening degree of a total → lunar eclipse. The five steps of the scale run from 0 (extremely dark, invisible Moon) to 4 (extremely bright, the eclipse having a very weak effect on the Moon's visibility). The darkening at a lunar eclipse is determined to a great extent by the transparency of the terrestrial atmosphere, which is affected by clouds and the dust from the volcanic eruptions (M.S.: SDE).

Named after André Danjon, who set up the scale, → Danjon astrolabe; → scale.

dare
  ۱) درشیدن؛ ۲) درشه   
1) daršidan; 2) darše

Fr.: 1) oser; 2) défi   

1) To be courageous enough to try to do something.
2) A challenge, especially to prove courage.

M.E. durren, from O.E. durran "be bold enough, have courage" (to do something); cf. O.Norse dearr, O.H.G. giturran, Gothic gadaursan, from PIE root *dhers- "bold" source also of O.Pers. darš-, as below.

Daršidan, from O.Pers. darš- "to dare," Av. darš- (prefixed *upa- in upadarəš- "to dare"); cf. Khotanese darv- "to dare;" Baluci durrit/durr- "to take courage;" Skt. dhars "to venture;" Gk. thrasus "bold;" Goth. ga-daursan "to venture;" E. "to dare;" PIE *dhers- "to attack, venture, dare" (Cheung 2007).

daring
  درشمند   
daršmand

Fr.: audacieux   

Taking or willing to take risks; audaciousness.

dare; → -ing.

dark
  تاریک   
târik (#)

Fr.: sombre, obscur, noir   

Having very little or no light.

M.E. derk, O.E. deorc, from P.Gmc. *derkaz.

Târik, Mid.Pers. târig "dark," târ "darkness," Av. taθra- "darkness," taθrya- "dark," cf. Skt. támisrâ- "darkness, dark night," L. tenebrae "darkness," Hittite taš(u)uant- "blind," O.H.G. demar "twilight."

dark adaptation
  نیاوش به تاریکی   
niyâveš bé târiki

Fr.: adaptation à l'obscurité   

The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination.

dark; → adaptation.

<< < -es -it -sc 201 951 abe abs abs aca acc acc aco act ada adh ado aer aft air Alf alg alk alp Alt alt amb ana And ang ani ann ant ant ant apo app app Apu arc arg Arn art ass ast ast ast atm ato att aur aut avo azi bac bal bar bar bat Bea Bel bet bia big bin bio Bir bla bla blo Blu bol Boo bou box bre Bri bro bur cal cal Can cap car Car cat cau cel cen cen cha Cha cha che Chi chr cir cir civ cla clo clo CMB coa coe coh col col col com com com com com com com com Com con con con con con con con con con con con con coo cor cor cor Cos cos cos cou cou cra cri cro cry cul cur cyc D l dar dat day dea dec dec dec def def deg Del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra Dsc dus dwa dyn Dys Ear ecc eco edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ eru eth Eur eve exa exc exe exi exo exp ext ext ext fab fai Fan fea fem fer fie fil fir fir fla fli flu foc for for for fra fre fre fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo Gib glo gov gra gra gra gra gre gro Gui H-a hal Ham har Hay hea hei hel Hel her het hie hig hoa hom hor hot Hub Hug hur hyd hyd hyl hyp ice ide ima ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv inv ion iro Isl iso iso Jab jet Jov Jup Kar Kep kil Kip Kra Lag Lam Lan Lar las law lea Leg Leo lev lig lim lin lin lin lit loc loc log Lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal map mas mas mat Mau mea mea med Men mer Mes Met met mic mic Mie mil min Mir mix mod mol mom Moo mor mov mul mur n-b nan nat nea neg Ner neu new New NGC noc nom non non nor nor nuc nuc nul nut obj obl obs occ oct off old one ope opp opt opt orb ord org Ori osc oth ove Owl P-s Pal par par par par Pas pat pec pen per per per per per Pha pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro pro pub pul pyc qua qua qua qua qui rad rad rad rad rad rad rai ran rar 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 S5- Sal sat sca sca Sch sci Scu sec sec sed sel sel sem seq set sha she sho sid sie sil sim sin sit sky slo sno sod sol sol sol sol son sou spa spa spe spe spe spe sph spi spo squ sta sta sta sta ste ste ste Sti sto str str sub sub sub sul sup sup sup sup sur sur syl syn sys tal Tay tel ten ter tex the the the the Tho thr tid tim Tit too Tor tra tra Tra tra Tra tri Tri tru tub tur two Typ ult ult unc uni uni uni upl ura uti val var vec vel ver Ver vie vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>