Fr.: lune bleue
The second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month. Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month. This happens every two and a half years, on average.
The folkloric term blue Moon for the calendrical event is new, and apparently goes back to the Maine Farmers' Almanac for 1937. But its original meaning in that work was the third full Moon in a season when there were four full Moons in that season. Some have related the term to the much older English expression moon is blue, which goes back to a couplet from 1528, interpreting it as "something that occurs rarely." However in that poem the expression had a meaning of "something that was absurd." Alternatively, the term blue Moon may have been borrowed from the Chinese lunar calendar particularly in its usage among American Chinese community. In fact in that calendar when there are two full Moons in a month they use the term "blue Moon" and add a thirteenth intercalary month. → blue; → moon.
Fr.: région bleue
The portion of the → visible spectrum lying between 455 and 492 nm.
âsmân-e âbi (#)
Fr.: ciel bleu
A phenomenon which results from → Rayleigh scattering of sunlight by → atmospheric molecules. → Nitrogen and → oxygen molecules that compose about 78% and 21% of the air, respectively, are small compared to the light → wavelengths, and thus more effective at scattering shorter wavelengths of light (blue and violet). The → selective scattering by these → molecules is responsible for producing the blue skies on a clear sunny day. The sky over the horizon appears much paler in color, because the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Hence, less blue light reaches the observer's eyes.
Fr.: traînarde bleue, traînard bleu
Any of stars, often found in → globular clusters and old → open clusters, that lie on the blueward extension of the → main sequence beyond the → turnoff point. Blue stragglers have an anomalously blue color and high luminosity in comparison with other cluster members. The most probable ways in which they could form are: → mass transfer or → coalescence in → close binary systems, encounters or collisions in overcrowded cores of globular clusters.
Fr.: supergéante bleue
Fr.: aile bleue
The → line wing with wavelengths shorter than that of the emission or absorption peak.
Fr.: décalage vers le bleu
The apparent shift of the wavelength towards the shorter wavelength region of the radiation spectrum of an approaching object due to the Doppler effect.
Fr.: composante décalée vers le bleu
A constituent of a composite astronomical object which has a motion directed towards the observer, as revealed by its spectrum.
1) (v.tr.) To make indistinct and hazy in outline or appearance.
Probably akin to M.E. bleren "to blear."
Târ "dark, obscure, cloudy" Mid.Pers. târ, from Mid./Mod.Pers. târ "dark, obscure, cloudy."
tasvir-e târ, ~ nâtig
Fr.: image estompée, ~ floue
In → galactic dynamics models, the → scattering of stars at radii substantially away from → corotation resonance, especially at the → Lindblad resonances, leading to a higher → eccentricity. The → spiral wave response of a → galactic disk to a co-orbiting mass → clump blurs the distinction between scattering by → spiral arms and by mass clumps. See also → churning (J. A. Sellwood & J. J. Binney, 2002, astro-ph/0203510 and references therein).
Verbal noun of → blur.
The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.
L. Boötes, from Gk. bootes "plowman," literally "ox-driver," from bootein "to plow," from bous "ox," from PIE *gwou- "ox, bull, cow;" compare with Av. gao-, gâuš "bull, cow, ox," Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.
Gâvrân "ox-driver," from gâv "ox, cow" + rân
"driver," from rândan "to drive."
Fr.: loi de Bode
Any material object characterized by its physical properties.
Body, from O.E. bodig "trunk, chest," related to O.H.G. botah, of unknown origin.
Jesm, from Ar. jism "body, corps."
Fr.: classification de Boeshaar-Keenan
A system for the classification of → S-type stars. The system involves the designations of a C/O index and a temperature type. Moreover, when possible, it uses intensity estimates for → ZrO bands, the → TiO bands, the → Na I D-lines, the YO bands, and the Li I 6708 line.
Philip C. Keenan & Patricia C. Boeshaar, 1980, ApJS, 43, 379; → classification.
Niels Bohr (1885-1962), Danish physicist who made several important contributions to modern physics. He won the 1922 Nobel prize for physics in recognition of his work on the structure of atoms.
Fr.: atome de Bohr
The simplest model of an atom according to which electrons move around the central nucleus in circular, but well-defined, orbits. For more details see → Bohr model.
magneton-e Bohr (#)
Fr.: magnéton de Bohr
A fundamental constant, first calculated by Bohr, for the intrinsic → spin magnetic moment of the electron. It is given by: μB = eħ/2me = 9.27 x 10-24 joule/tesla = 5.79 x 10-5 eV/tesla, representing the minimum amount of magnetism which can be caused by the revolution of an electron around an atomic nucleus. It serves as a unit for measuring the magnetic moments of atomic particles.
Fr.: modèle de Bohr
A model suggested in 1913 to explain the stability of atoms which classical electrodynamics was unable to account for. According to the classical view of the atom, the energy of an electron moving around a nucleus must continually diminish until the electron falls onto the nucleus. The Bohr model solves this paradox with the aid of three postulates (→ Bohr's first postulate, → Bohr's second postulate, → Bohr's third postulate). On the whole, an atom has stable orbits such that an electron moving in them does not radiate electromagnetic waves. An electron radiates only when making a transition from an orbit of higher energy to one with lower energy. The frequency of this radiation is related to the difference between the energies of the electron in these two orbits, as expressed by the equation hν = ε1 - ε2, where h is → Planck's constant and ν the radiation frequency. The electron needs to gain energy to jump to a higher orbit. It gets that extra energy by absorbing a quantum of light (→ photon), which excites the jump. The electron does not remain on the higher orbit and returns to its lower energy orbit releasing the extra energy as radiation. Bohr's model answered many scientific questions in its time though the model itself is oversimplified and, in the strictest sense, incorrect. Electrons do not orbit the nucleus like a planet orbiting the Sun; rather, they behave as → standing waves. Same as → Bohr atom.
Fr.: rayon de Bohr
The radius of the orbit of the hydrogen electron in its ground state (0.529 Å).