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.
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).
calcium break index
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).
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.
A conventional notation for decimal exponent, which converts the number after it into its common antilogarithm; for example, dex (2.35) = 102.35.
From decimal + exponent.
Fr.: dextro-, dextr-
A combining form meaning "right" and "turning clockwise," used in the formation of compound words, e.g. → dextrorotatory, dextrocardia, dextrocular, etc. The variant dextr- occurs before vowels. Compare → levo-.
From L. dextr-, from dexter "right, right-hand;" cf. Gk. dexios "right," dexiteros "located on the right side;" Av. dašina- "right; south" ( Mid.Pers. dašn "right hand; " Ossetic dæsni "skillful, dexterous"); Skt. dáksina- "right; southern;" Goth. taihswo "right hand;" O.Ir. dess "on the right hand, southern;" PIE base *deks- "right;" + epenthetic vowel -o-; see also → south.
Râst- from râst, → right.
Adj. related to → dextrorotation.
Fr.: indice de dispersion
The reciprocal of the → dispersive power.
dastnevešt-e Dresden (#)
Fr.: codex de Dresden
A pre-Colombian Maya manuscript consisting of numerous calendar and astronomical data, probably dating from the 12th century. It seems that it is an updated copy of a document from the period of the old Maya Empire (4th-9th centuries). It contains a table which covers over 32 years, grouping 45 successive → lunations, divided into 69 groups of 5 or 6 lunations. The data are calculated in days and correspond remarkably to the intervals in an eclipse table: each group ends at the probable date of a solar eclipse (M.S.: SDE).
Dresden refers to the Dresden Library where the original document is preserved. It was bought in 1739 by the library director, Johann Christian Götze, who found it in a private library in Vienna. Its earlier history is unknown; codex, from L. codex earlier caudex "book, book of laws," literally "tree-trunk, book (formed originally from wooden tablets)."
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.
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.
Index Catalogue (IC)
Fr.: Index Catalogue
Either of two catalogues of non-stellar objects, which serve as supplements to the → New General Catalogue.
index of refraction
Fr.: indice de réfraction
Same as → refractive index.
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.
Fr.: index polytropique
A number appearing in the equation describing a → polytropic process.
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).
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.
relative refractive index
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.
Fr.: indice spectral
1) The → exponent
of the → frequency on which depends
the intensity of the → continuum emission, that is:
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.
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.