An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 16 Search : index
adiabatic index
  دیشن ِ بی‌دررو   
dišan-e bidarrow

Fr.: indice adiabatique   

Of a gas, the ratio of its → specific heat at constant pressure to its specific heat at constant volume: γ = CP/ CV.

adiabatic; → index.

braking index
  دیشن ِ لگامش   
dišan-e legâmeš

Fr.: indice de freinage   

A parameter indicating the rate at which a → pulsar slows down. Neutron stars are powered by → rotational energy and lose energy by accelerating particle → winds and by emitting → electromagnetic radiation. The → rotation frequency, Ω, thus decreases with time and this slowdown is usually described by the relation Ω. = - kΩn, where k is a positive constant which depends on the → moment of inertia and the → magnetic dipole moment of the → neutron star and n is the braking index. Conventionally, the braking index is derived by differentiation of the above equation, yielding n = ΩΩ.. / Ω.2. In a highly simplified model in which the spin-down torque arises from dipole radiation at the rotation frequency, one expects n = 3 (Johnston, S., Galloway, D., 1999, arXiv:astro-ph/9905058).

braking; → index.

calcium break index
  دیشن ِ گسست ِ کلسیوم   
dišan-e gosast-e kalsiom

Fr.: indice de la coupure de calcium   

The strength of the → calcium break, as measured from the fluxes in the intervals 3750-3950 Å and 4050-4250 Å. It is given by the expression Ca-break[%] = 100 · (fupper - flower)/fupper, where fupper and flower are the mean fluxes measured in the 3750-3950 Å and 4050-4250 Å bands, respectively, in the rest frame (Dressler & Shectman 1987, AJ 94, 899).

calcium; → break; → index.

color index
  دیشن ِ رنگ   
dišan-e rang

Fr.: indice de couleur   

The difference between the → apparent magnitude of a star measured at one standard wavelength and the apparent magnitude at another longer, standard wavelength, allowing the quantitative measure of a star's color.

color; → index.

dispersive index
  دیشن ِ پاششی   
dišan-e pâšeši

Fr.: indice de dispersion   

The reciprocal of the → dispersive power.

dispersive; → index.

  ۱، ۲، ۳) دیشن؛ ۴) فهرست   
1, 2, 3) dišan; 4) fehrest (#)

Fr.: 1, 2) indice; 3) index   

1) Math.: A number or symbol, often written as a → subscript or → superscript to a mathematical expression, that indicates an operation to be performed, an ordering relation, or a use of the associated expression.
2) Physics: A measure of a particular property; e.g. → adiabatic index; → color index; → index of refraction.
3) In some → astrolabes, the → rule.
4) A sequential arrangement of items, especially in alphabetical or numerical order. → Index Catalogue.

Index, from L. index "forefinger, pointer, sign," literally "anything which points out," from indicare "point out, show," from in- "in" + dicare "to proclaim," from stem of dicere "to speak, to say;" PIE base *deik- "to point out" (cf. Av. daēs- " to show;" Skt. dic- "to point out, show;" Gk. deiknynai "to prove;" O.H.G. zeigon; Ger. zeigen "to show;" O.E. teon "to accuse," tæcan "to teach").

1) Dišan, from diš-, simple aorist of Av. daēs- "to show," as above, + suffix -an.
2) Fehrest, from Mid.Pers. payrâstag "arranged," from payrâstan "to arrange; to adorn" (Mod.Pers. pirâstan); Proto-Ir. *pati-rāsta-, from *pati "to, at, for, in" (cf. Mid.Pers. pad "to, at, for, in;" Mod.Pers. be, beh; Old.Pers. paity; Av. paiti "to, toward, in, at;" Skt. práti; Gk. poti) + *rād- "to direct, arrange" (cf. Mod.Pers. raj "line, row," variants raž, rak, râk, rezg (Lori), ris, risé, radé, rasté, râsté, related to râst "right, true; just, upright, straight;" Mid.Pers. râst "true, straight, direct;" Sogdian rəšt "right;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" PIE base *reg- "move in a straight line," hence, "to direct, rule").

Index Catalogue (IC)
  کاتالوگ ِ فهرست   
kâtâlog-e fehrest

Fr.: Index Catalogue   

Either of two catalogues of non-stellar objects, which serve as supplements to the → New General Catalogue.

index; → catalog

index of refraction
  دیشن ِ شکست   
disšan-e šekast

Fr.: indice de réfraction   

Same as → refractive index.

index; → refraction.

multipole index
  دیشن ِ بس‌قطبه   
dišan-e basqotbé

Fr.: indice multipolaire   

A variable used in → spherical harmonic expansions. Each spherical harmonic is characterized by its multipole index l: l = 0 for a → monopole, l = 1 for a → dipole, and so on. It is used in particular to describe the → cosmic microwave background anisotropy: ΔT/T0 (θ,φ) = Σ almYlm(θ,φ), where θ and φ are the → spherical polar coordinates, Ylm is the → spherical harmonic functions, and the sum runs over l = 1, 2, ..., ∞ and m = -l, ..., l, where the multipole index l corresponds to angular scales ≅ 180°/l.

multipole; → index.

polytropic index
  دیشن ِ بُلگشت   
dišan-e bolgašt

Fr.: index polytropique   

A number appearing in the equation describing a → polytropic process.

polytropic; → index.

Q index
  دیشن ِ Q   
dišan-e Q

Fr.: indice Q   

In the Johnson → UBV system, a reddening-free parameter which is related to the → effective temperature of stars and thus provides a useful, but rough, discriminant for → spectral types. It is expressed as: Q = (U - B) - 0.72 (B - V).


refractive index
  دیشن ِ شکست   
dišan-e šekast

Fr.: indice de réfraction   

Of any optical medium, the ratio of the → speed of light in vacuum (c) to that in the medium (v): n = c/v. The refractive index for vacuum, by definition, is 1. The refractive index of air is 1.00029 at standard temperature (25 °C) and pressure (1 atm). The refractive index of a medium depends on the wavelength of refracted wave. With light waves, n increases as the wavelength decreases. → Snell's law can be used to derive n. Same as → index of refraction.

Refractive, pertaining to → refraction; → index.

relative refractive index
  دیشن ِ شکستی ِ بازانی   
dišan-e šekasti-ye bâzâni

Fr.: indice de réfraction relatif   

The ratio of the sine of the angle of incidence to the sine of the angle of refraction for a ray passing out of one of the media into the other.

relative; → refractive; → index.

spectral index
  دیشن ِ بینابی   
dišan-e binâbi

Fr.: indice spectral   

1) The → exponent of the → frequency on which depends the intensity of the → continuum emission, that is: Fν∝ να. The exponent (α) typically takes positive values from 0 to 2 for → thermal emission, while → non-thermal emission, such as → synchrotron radiation, leads to negative values of the spectral index ranging from about -0.5 to -1.5.
2) The ratio αIR = dlog(λFλ)/dlogλ, where F represents the flux and λ the wavelength, in the range 2.2 μm ≤ λ ≤ 25 μm, particularly used in the classification of → protostars (→ Class I, → Class II, and → Class III).

spectral; → index.

variability index
  دیشن ِ ورتندگی   
dišan-e vartandegi

Fr.: indice de variabilité   

A measure of variability of a star (such as Welch-Stetson variability index) which combines the information from two passbands assuming that changes in the star's luminosity occur nearly simultaneously at all optical wavelengths.

variability; → index.

volcanic explosivity index (VEI)
  دیشن ِ اسکفتندگی ِ آتشفشانی   
dišan-e oskaftandegi-ye âtašfešâni

Fr.: indice d'explosivité volcanique   

A logarithmic scale, ranging from 1 to 8, used to measure the intensity of volcano eruptions. The VEI is based on several factors: the degree of fragmentation of the volcanic products released by the eruption, the amounts of sulfur-rich gases that form stratospheric aerosols, the volume of the eruptions, their duration, and the height is reached. The largest eruptions (8) produce an amount of bulk volume of ejected → tephra of ~ 1,000 km3.

volcanic; → explosivity; → index.