Fr.: densité de flux
Flux of radiation that falls on a detector per unit surface area of the detector per unit bandwidth of the radiation per unit time.
Fr.: transition interdite
Global Positioning System (GPS)
râžmân-e nehešdâd-e jahâni
Fr.: système de positionnement par satellites
A coordinate positioning tool, using a combination of satellites that can rapidly and accurately determine the → latitude, → longitude, and the → altitude of a point on or above the Earth's surface. The GPS is based on a constellation of 24 Earth-orbiting satellites at an altitude of about 26,000 km. The system is a direct application of the thories of → special relativity and → general relativity.
H II region luminosity
tâbandegi-ye nâhiye-ye H II
Fr.: luminosité de région H II
The total number of → Lyman continuum photons emitted by an → H II region. It is usually derived using → radio continuum observations which are less affected by → interstellar extinction. The measured value is often a lower limit because of photon leakage from the H II region and absorption. See also → density-bounded H II region.
Fr.: transition hyperfine
1) The laying on of something as a burden or obligation.
dar jâ (#)
Fr.: in situ
Situated in the natural or original position or place.
Dartanuyi state, condition noun of dartanu, → intense.
intensity of a line
Fr.: intensité de raie
The height of a spectral line above the continuum base.
intensity of radiation
Fr.: intensité de rayonnement
The rate of emitted energy from unit surface area through unit solid angle. The radiation from a surface has different intensities in different directions.
Fr.: luminosité intrinsèque
The energy per second emitted by an astronomical object.
Fr.: viscosité cinématique
The ratio of the → dynamic viscosity (η) to the density (ρ) of a fluid: ν = η/ρ. The unit of kinematic viscosity in the → SI system is m2s-1. In the → cgs system, cm2s-1, equal to 10-4 m2s-1, is called the → stokes (st).
Fr.: densité lagrangienne
A quantity, denoted Ld, describing a continuous system in the
→ Lagrangian formalism, and defined as the
→ Lagrangian per unit volume.
It is related to the Lagrangian L by:
Fr.: intensité de raie
A measure of the total effect of an absorption or emission line. The line intensity is equal to the integration of the absorption coefficient over the entire shape of the absorption line.
local position invariance
nâvartâyi-ye neheš-e mahali
Fr.: invariance de position locale
The → total → brightness
of a star or other astronomical object.
It is expressed in watts and represents the total amount of
→ energy that the object radiates each
→ second over all
wavelength regions of the → electromagnetic spectrum.
Because this quantity is independent of distance, it is an
→ intrinsic brightness.
Verbal noun of → luminous.
rade-ye tâbandegi (#)
Fr.: classe de luminosité
A classification of stellar spectra according to luminosity for a given → spectral type. The luminosity class is an indication of a star's → surface gravity. It is shown by a Roman numeral as follows: I (→ supergiants), II (bright → giants), III (normal giants), IV (→ subgiants), and V (→ dwarf stars, or → main-sequence stars). Luminosity classes VI (→ subdwarfs) and VII (→ white dwarfs) are rarely used. Subclasses a, b, and c are especially used for supergiants, while the most luminous → hypergiants are assigned luminosity class Ia-0.
Fr.: distance de luminosité
1) Distance derived by comparison of → observed and
→ intrinsic luminosities.
If an object has a known luminosity L, and the observed flux is
S, the luminosity distance is defined by
DL = (L/4πS)1/2.
Fr.: fonction de luminosité
Number → distribution of → stars or galaxies (→ galaxy) with respect to their → absolute magnitudes. The luminosity function shows the → number of stars of a given intrinsic luminosity (or the number of galaxies per integrated magnitude band) in a given → volume of space.