Fr.: anneau B
One of → Saturn's rings, lying beyond the → C ring and before the → A ring, extending from 92,000 to 117,300 km (width 25,300 km) from the center of Saturn. The B ring is bounded by the → Huygens Division.
setâre-ye B (#)
Fr.: étoile B
A star of → spectral type B, whose spectrum is marked by absorption lines of hydrogen; also known as B-type star. B-type optical spectra are characterized by the presence of neutral He lines (mainly He I 4471 Å) at about type B9. He I strengthens up to about B2, then decreases. Ionized helium (mainly He II 4541 Å) first appears at about B0. Most metallic lines are absent or weak, except some absorption lines for the higher ionization states of → silicon, → oxygen, → carbon, and → magnesium. These are hot stars with → effective temperatures ranging from about 10,000 K at B9 to nearly 30,000 K at B0. They are between 3 and 20 → solar masses. Some famous examples include: → Rigel, → Achernar, → Hadar.
qotbeš-e tarz-e B
Fr.: polarisation en mode B
A → polarization component in the → cosmic microwave background radiation that depends only on → curl, is independent of → gradient, and has → handedness that distinguishes left from right. The B-mode is due to only → vector perturbations or → tensor perturbations. It has two types, the first type, which constitutes the majority of the B-mode polarization, results from → lensing by galaxies that twist the → E-mode polarized light on its journey from the other side of the → observable Universe. The second type can be produced only by → gravitational waves, not by density perturbations. This type of B-mode is incredibly faint, producing temperature variations of about 0.4 microK and accounting for just one part in 10 million in the CMB temperature distribution. It is expected to be generated during cosmic → inflation shortly after the → Big Bang. The → BICEP2 team announced in March 2014 that they had detected the second type of B-modes, consistent with inflation and gravitational waves in the → early Universe. The detected degree scale B-mode polarization has a tensor-to-scalar ratio, r = 0.2 (+0.07, -0.05), which is a measure of the amplitude of the primordial gravitational waves.
sayyârak-e gune-ye B
Fr.: astéroïde de type B
A division of → C-type asteroids whose members have relatively low albedos (0.04 to 0.08) and the → ultraviolet absorption below 0.5 μm is small or absent. Examples include → 2 Pallas, 379 Huenna (diameter 62 km), and → 101955 Bennu.
setâre-ye gune-ye B
Fr.: étoile de type B
Same as → B star.
Fr.: fenêtre de Baade
An area of the sky with relatively low amounts of → interstellar dust along the → line of sight, occurring toward the → constellation of → Sagittarius, near the → globular cluster NGC 6522. The window, through which stars in the → Galactic bulge are visible, lies 3.9 degrees south of the → Galactic center, corresponding to a line of sight that passes within 1,800 → light-years of the → Milky Way's core. It is named after Walter Baade, who used it to observe → RR Lyrae stars in the → Galactic bulge region.
raveš-e Bâdé-Veselink (#)
Fr.: méthode de Baade-Wesselink
A method used to determine the size of certain types of pulsating stars, including Cepheids, from their magnitude variations (photometry) and the corresponding radial velocities (spectroscopy).
Baade, from Walter (Wilhelm Heinrich) Baade (1893-1960), German/American astronomer, who made important contributions to the research on variable stars; Wesselink, from Adriaan J. Wesselink (1909-1995), Dutch/American astronomer, the originator of the method. → method.
Fr.: compensateur de Babinet
A crystal device made of two → quartz → prisms with equal acute angles assembled in a rhombus that is used in analyzing → polarized light. The wedge-shaped prisms are placed against each other and can be displaced along their plane of contact by a → micrometer. Thus they form a parallel plate of variable thickness allowing the optical retardation to be adjusted.
Jacques Babinet (1794-1872), French physicist; → compensator.
Fr.: point de Babinet
Fr.: principe de Babinet
pas (#), pošt (#)
Fr.: dos, arrière
1) General: Related to or located at the back
"the side or surface opposite the front or face."
Back, from M.E., from O.E. bæc; akin to O.H.G. bah "back."
Pas-, from pas "behind" (e.g.: pas-e pardé
"behind the curtain"); Mid.Pers. pas "behind, before, after;"
O.Pers. pasā "after;" Av. pasca "behind (of space);
then, afterwards (of time);" cf.
Skt. paścā "behind, after, later;" L. post "behind,
in the rear; after, afterwards;"
O.C.S. po "behind, after;" Lith. pas "at, by;"
PIE *pos-, *posko-.
In a radiotelescope, the unit forming the end part of the reception chain. It generally consists of a spectrometer and performs frequency analysis of the signals. → front-end.
Back-end, from → back + end, from M.E., O.E. ende (cf. Du. einde, O.H.G. enti "top, forehead, end," Ger. ende, Goth. andeis "end"), originally "the opposite side," from PIE *antjo "end, boundary," from base *anta-/*anti- "opposite, in front of, before."
Pas-tah, from pas, → back, + tah "end," Mid.Pers. tah "bottom." The origin of this term is not clear. It may be related to Gk. tenagos "bottom, swamp," Latvian tigas<*tingas < *tenegos "depth," PIE *tenegos "water bottom."
paszaminé, zaminé (#)
General: That part of a view or scene that serves as a setting
for the main objects, persons, etc.
Background, from → back + ground, from M.E., from O.E. grund; akin to O.H.G. grunt "ground."
nufe-ye paszaminé, ~ zaminé
Fr.: bruit du fond
An unwanted signal in a system which is producing or recording a signal. For instance, a randomly fluctuating signal superimposed on the signal from a cosmic radio source.
tâbeš-e paszaminé, ~ zaminé
Fr.: rayonnement du fond
1) pas-parâkandan; 2), 3) pas-parâkaneš
1) (v.tr.) To deflect photons or particles in a direction opposite
to their initial path.
Fr.: lumière rétrodiffusée
The light that has undergone → backscattering.
Scattering of radiation or particles through angles greater than 90° with respect to the original direction of motion.
A copy of computer files that is stored separately from the original in order to protect against loss of data.
Backup "substitute, support," from → back + up.
Poštvân "prop, support, help" from pošt, → back, + -vân suffix denting protection, variant of -bân.
barnâme-ye yadaki (#)
Fr.: programme de remplacement
An auxiliary observing program to be carried out at telescope in case the atmospheric conditions make the main program unfeasible.
Barnâmé, → program; yadaki "reserve, substitute," from yadak "a led horse."