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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Jablonski diagram
  نمودار ِ یابلونسکی   
nemudâr-e Jablonski

Fr.: diagram de Jablonski   

An energy schematic representing the → electronic states of a → molecule and the → transitions between them. The vertical axis shows energies whereas → energy states are grouped horizontally according to their spin → multiplicity. Radiation-less transitions are symbolized by usual arrows, while → radiative transitions are represented by wavy arrows. The vibrational ground states of each electronic state are indicated with thick lines and the higher → vibrational states with thinner lines.

Named after Aleksander Jablonski (1898-1980), a Polish physicist who was an expert in the field of luminescence and atomic optics; → diagram.

Jacobi integral
  درستال ِ یاکوبی   
dorostâl-e Jacobi

Fr.: intégrale de Jacobi   

The integral admitted by the equations of a body of infinitesimal mass moving under the → gravitational attractions of two massive bodies, which move in circles about their → center of gravity. The Jacobi integral is the only known conserved quantity for the circular → restricted three-body problem. In the co-rotating system it is expressed by the equation: (1/2) (x·2 + y·2 + z·2) = U - CJ, where the dotted coordinates represent velocities, U is potential energy, and CJ the constant of integration (→ zero-velocity surface). The Jacobi integral has been used for two different purposes: 1) to construct surfaces of zero velocity which limit the regions of space in which the small body, under given initial conditions, can move, and 2) to derive a criterion (→ Tisserand's parameter) for re-identification of a → comet whose orbit has suffered severe perturbations by a planet. Also known as Jacobi constant.

Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics; → integral.

Jacobian
  یاکوبی   
Jacobi

Fr.: jacobien   

Jacobian determinant, → Jacobian matrix.

Named after Karl Gustav Jacobi (1804-1851), a German mathematician who did important work on elliptic functions, partial differential equations, and mechanics. The "Jacobian" first appeared in an 1815 paper of the French mathematician Augustin Louis Cauchy (1789-1857), but Jacobi did write a detailed memoir about it in 1841.

Jacobian determinant
  آترمگر ِ یاکوبی   
âtarmgar-e Jacobi

Fr.: déterminant jacobien   

The determinant of a → Jacobian matrix formed by the n2 → partial derivative s of n functions of n variables.

Jacobian; → determinant.

Jacobian matrix
  ماتریس ِ یاکوبی   
mâtris-e Jacobi

Fr.: matrice jacobienne   

In → vector calculus, the matrix of all → first-order partial derivatives of a vector-valued → function.

Jacobian; → matrix.

Jalali calendar
  گاهشمار ِ جلالی   
gâhšomâr-e Jalâli (#)

Fr.: calendrier jalali   

An Iranian solar calendar, based on two successive passages of the Sun through the true → vernal equinox. It results from a reform undertaken by a group of astronomers led by Omar Khayyam (A.D. 1048-1131). The current → Iranian calendar is an improved version of the Jalali calendar.

Jalali, from the name of the ruler Jalâleddin Malek Šâh of the Saljuqid dynasty, who ordered the reform; → calendar.

James Webb Space Telescope (JWST)
  دوربین ِ فضایی ِ جیمز وب، تلسکوپ ~ ~ ~   
durbin-e fazâyi-ye James Webb, teleskop ~ ~ ~

Fr.: Télescope spatial James Webb   

A large, infrared space telescope with a mirror 6.55 m in diameter, scheduled for launch in 2018. JWST's instruments will work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range (0.6 to 28 μm). The scheduled instruments are Near IR Camera (NIRCam, field of 2.2 x 4.4 arcmin, wavelength range 0.6-5 μm), Near IR Spectrograph (NIRSpec, 3.5 x 3.5 arcmin, 0.6-5 μm, resolving powers of ~ 100, ~1000, and ~3000), Mid IR Instrument (MIRI, 1.4 x 1.9 arcmin, 5-27 μm, R ~ 3000), and Fine Guidance Sensor (FGS, 2.3 x 2.3 arcmin, 0.6-5 μm, R ~ 100). The successor to the → Hubble Space Telescope will be placed in an orbit about 1.5 million km from the Earth, at the → Lagrangian point L2. The JWST project is a → NASA-led international collaboration with the → European Space Agency and the Canadian Space Agency. The scientific goals of JWST can be grouped under four broad topics: first light after the Big Bang; galaxy formation; birth of stars and protoplanetary systems; and planetary systems and the origins of life.

Named in honor of James E. Webb (1906-1992), who headed NASA from 1961 to 1968, overseeing all the manned launches in the Mercury through Gemini programs, until before the first manned Apollo flight; → space; → telescope.

jansky (Jy)
  جنسکی   
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.

Janus
  یانوس   
Yânus (#)

Fr.: Janus   

The sixth of Saturn's known satellites. With a mean diameter of about 178 km it orbits Saturn at a distance of 150,000 km. Discovered by the French astronomer Audouin Dollfus (1924-) in 1966.

Janus was the god of gates and doorways in Roman mythology. He was also thought to represent beginnings, hence he lent his name to January, the first month of the year. He was depicted with two faces looking in opposite directions.

jasper
  یشم   
yašm (#)

Fr.: jaspe   

A colored form of natural silica, SiO2, which is a precious stone.

M.E. jaspe, jaspre, from M.Fr., O.Fr. jaspe, from L. iaspidem (nominative iaspis), from Gk. iaspis "jasper," via an Oriental language, probably an Eastern Iranian language, see below.

Yašm, variants, yasp, yasb, yašf "jasper;" Sogd. iešp "jasper," iešpênê "of jasper, crystalline."

Jeans
  جینز   
Jeans

Fr.: Jeans   

Sir James Hopwood Jeans (1877-1946), English mathematical physicist, astrophysicist, and popularizer of science. He made important contributions to theoretical astrophysics, especially to the theory of stellar formation. → Jeans escape, → Jeans instability, → Jeans length, → Jeans mass, → Jeans scale, → Rayleigh-Jeans law, → Rayleigh-Jeans spectrum, → thermal Jeans mass, → turbulent Jeans mass, → Jeans escape.

Jeans escape
  گریز ِ جینز   
goriz-e Jeans

Fr.: échappement de Jeans   

A → thermal escape process by which the atmosphere of a planet loses gases to outer space. This form of thermal escape occurs because some molecules, especially low mass ones, are within the higher-velocity end of the → Maxwell-Boltzmann distribution. The possibility for the gases to escape occurs when the thermal energy of air molecules becomes greater than the → gravitational potential energy of the planet: (3/2)kT = (1/2)mv2  >  GmM/R where v is upward velocity of a molecule of mass m, M is the mass of the planet, and R is the radius of the planet at which thermal escape occurs. The minimum velocity for which this can work is called the → escape velocity is: ve = (2MG/R)1/2. Hydrogen molecules (H2) and helium, or their ions tend to have velocities high enough so that they are not bound by Earth's gravitational field and are lost to space from the top of the atmosphere. This process is important for the loss of hydrogen, a low-mass species that more easily attains escape speed at a given temperature, because v ~ (2kT/m)1/2. As such, Jeans' escape was likely influential in the atmospheric evolution of all the early terrestrial planets. Jeans' escape currently accounts for a non-negligible fraction of hydrogen escaping from Earth, Mars, and Titan, but it is negligible for Venus because of a cold upper atmosphere combined with relatively high gravity (see, e.g., Catling, D. C. and Kasting, J. F., 2017, Escape of Atmospheres to Space, pp. 129-167. Cambridge University Press).

Jeans; → escape.

Jeans instability
  ناپایداری ِ جینز   
nâpâydâri-ye Jeans

Fr.: instabilité de Jeans   

An instability that occurs in a → self-gravitating  → interstellar cloud which is in → hydrostatic equilibrium. Density fluctuations caused by a perturbation may condense the material leading to the domination of gravitational force and the cloud collapse. The advent of instability involves a threshold called the → Jeans length or the → Jeans mass.

Jeans; → instability.

Jeans length
  درازای ِ جینز   
derâzâ-ye Jeans (#)

Fr.: longueur de Jeans   

The critical size of a homogeneous and isothermal interstellar cloud above which the cloud is unstable and must collapse under its own gravity. Below this size the cloud's internal pressure is sufficient to resist collapse. The Jeans length is defined by: λJ = (π cs2/Gρ)1/2 = 0.2 pc (T/10 K)1/2(nH2/104 cm-3)-1/2, where cs is the → sound speed, G is the → gravitational constant, ρ is the gas density, T is the gas temperature, and nH2 is the molecular hydrogen density.

Jeans; → length.

Jeans mass
  جرم ِ جینز   
jerm-e Jeans (#)

Fr.: masse de Jeans   

The → minimum mass for an → interstellar cloud below which the → thermal pressure of the gas prevents its → collapse under the force of its own → gravity. It is given by the formula MJ = (π5/2 / 6) G -3/2ρ0-1/2cs3, where G is the → gravitational constant, ρ0 the initial → density, and cs the isothermal → sound speed. It can be approximated to MJ ~ 45 (TK) 3/2 (ncm-3) -1/2 in units of solar masses, where TK is the temperature in → Kelvin, and ncm-3 the gas density per cm3. High density favors collapse, while high temperature favors larger Jeans mass. See also: → thermal Jeans mass, → turbulent Jeans mass.

Jeans; → mass.

Jeans scale
  مرپل ِ جینز   
marpel-e Jeans

Fr.: échelle de Jeans   

Same as → Jeans length.

Jeans; → scale.

jelly
  ژله   
želé (#)

Fr.: gelée   

1) A soft somewhat elastic food product made usually with gelatin or pectin; especially, a fruit product made by boiling sugar and the juice of fruit.
2) A substance resembling jelly in consistency (Merriam-Webster.com).

M.E. gely, from O.Fr. gelee "a jelly," from L. gelare "to freeze, congeal, stiffen," from PIE *gel- "cold; to freeze."

Želeh, loan from Fr., as above.

jellyfish
  مدوسا، عروس ِ دریایی   
medusâ, arus-e daryâyi

Fr.: méduse   

Any of various marine coelenterates of a soft, gelatinous structure, especially one with an umbrella like body and long, trailing tentacles; medusa (dictionary.com).

jelly; → fish.

Medusâ, from Gk. Medousa, literally "guardian," from medein "to protect, rule over."

jellyfish galaxy
  کهکشان ِ مدوسا   
kahkešên-e medusâ

Fr.: galaxie méduse   

A type of galaxy exhibiting "tentacles" (tails) of material that appear to be stripped from the main body of the galaxy, making it resemble a jellyfish. Such type of galaxies occur in → galaxy clusters and are produced by a process called → ram pressure stripping. The mutual → gravitational attraction between galaxies causes them to fall at high speed into the clusters, where they encounter a hot → intracluster medium (ICM) with dense gas. The falling galaxy feels a powerful wind, forcing tails of gas out of the galaxy's disk and triggering → starbursts within it. Jellyfish galaxies have mainly been observed in nearby clusters (e.g., Virgo, Coma, A1367, A3627, Shapley). A few examples have been identified in clusters at → redshifts z ~ 0.2-0.4, and there is accumulating evidence for a correlation between the efficiency of the stripping phenomenon and the presence of shocks and strong gradients in the X-ray → intergalactic medium (Poggianti et al., 2016, AJ 151, 78).

jellyfish; → galaxy.

jet
  ۱، ۲، ۳) اِشان، شان؛ ۴) جت   
1, 2, 3) ešân, šân; 4) jet

Fr.: jet   

1) A stream of a liquid, gas, or small solid particles forcefully shooting forth from a nozzle, orifice, etc.
2) Fountain-like formations of gas and/or dust gushing out from compact regions of some astronomical objects. → astrophysical jets.
3) Meteo.: A common abbreviation for → jet stream.
4) Shortened of → jet plane.

Jet, from M.Fr. jeter "to throw," from V.L. *jectare, alter. of L. jactare, from jac- "throw" + -t- frequentative suffix + -are infinitive suffix; PIE base *ye- "to do" (cf. Gk. hienai "to send, throw;" Hittite ijami "I make").

Ešân, from ešândan, → eject; šân contraction of ešân.

<< < -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 > >>