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The largest → comet orbiting periodically around the → Sun. Its nucleus is about 26 km across and its orbital period 133 years. Comet Swift-Tuttle is the parent body of the → meteor shower called the → Perseids. The comet was discovered in July 1862, when it was apparently as bright as → Polaris in the night sky. The comet's reappearance was predictaed for 1992, when it was rediscovered by Japanese amateur astronomer Tsuruhiko Kiuchi. In 2126 it will be a bright naked-eye comet when it will come within about 23 million km of Earth, or about 60 times the distance from Earth to the Moon. Its nearest approach to Earth is expected in 3044, when the comet will come within 1.6 million kilometres of the Earth's surface.
Named after the American astronomers who independently discovered the comet in 1862, Lewis Swift (1820-1913) on July 16, and Horace Parnell Tuttle (1837-1923) on July 19.
accurate to n significant digits
rašmand bâ n raqam-e nešânâr
Fr.: écrit avec n chiffres significatifs
An expression specifying the number of meaningful digits used to express the value of a measured quantity. Same as accurate to n significant figures. For example, e = 2.71828 ... = 2.718 is rounded to four significant digits, and 2.72 to three significant digits. → accurate to n decimal places.
→ accurate; → significant; → digit.
Fr.: diffusion ambipolaire
A physical process which allows a → molecular cloud to decouple from → interstellar magnetic field in order to undergo → gravitational collapse. A cloud of pure molecular gas would form stars very fast through collapse since neutral matter does not respond to the magnetic field. However, the magnetic field holds up a collapse because the ions present in the cloud collide with the neutrals and tie them to the field. The collapse can then only proceed if the magnetic field can be separated from the gas. In denser molecular cores the ionization degree decreases substantially and therefore neutrals and ions decouple.
dâmane-dehi, dâmane-giri (#)
1) General: The act or result of amplifying, enlarging, or extending.
Verbal noun of → amplify.
Fr.: facteur d'amplification
1) Electronics: The extent to which an
→ analogue → amplifier
boosts the strength of a → signal. Also called
→ amplification; → factor.
Device for reproducing an electrical input at increased intensity.
Agent noun of → amplify.
dâmané dâdan, dâmané gereftan (#)
General:To make larger, greater, or more powerful.
From M.F. amplifier, from L. amplificare "to increase, augmant," from L. amplus "wide, large."
Dâmané, → amplitude; dâdan "to give" (Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" Skt. dadáti "he gives," Gk. didomi "I give," tithenai "to put, set, place;" L. dare "to give, offer;" Rus. delat "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do"); gereftan "to take, seize, catch," (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").
angular differential imaging (ADI)
tasvigari-ye degarsâne-yi-ye zâviye-yi
Fr.: imagerie différentielle angulaire
A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556).
→ angular; → differential; → imaging.
Fr.: décalage anormal vers le rouge
The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.
A property possessed by some → metals, → alloys, and salts of transition elements in which there is a lack of → magnetic moment due to the antiparallel or spiral arrangement of atomic → magnetic moments.
→ anti- + → ferromagnetism.
Fr.: Rift de l'Aigle
A long, dark structure located close to the → Galactic plane and occupying an area between longitudes l ~15° and ~35° and latitudes b ± 10° in the constellations Aquila, Serpens, and eastern Ophiuchus. The Aquila Rift is a complex of dust and → molecular clouds making part of → Gould's Belt in the → Orion Arm. The mass of the molecular gas, derived from → carbon monoxide (CO) observations (Dame et al. 2001, ApJ 547, 792), is in the range ~ 1-3 x 105 → solar masses. A distance of ~260 pc has been estimated for the Aquila Rift, but it is uncertain. Recent Herschel observations have revealed a filamentary structure in the Aquila Rift and the presence of a population of → pre-stellar cores as well as → young stellar objects (André et al. 2010, A&A 518, L102; Bontemps et al. 2010, A&A 518, L85; Könyves et al. 2010, A&A 518, L106).
Fr.: objet fabriqué, artefact
1) An object made by a human being, typically one of cultural or historical
From It. artefatto, from L. arte "by skill" (ablative of ars "→ art") + factum "thing made," from facere "to make, do," → -fy.
Dasâc "hand made," from das variant of dast, → hand, + sâc, variant of sâz-, sâxtan, → agree.
Not occurring naturally; produced by man.
M.E., from O.Fr., from L. artificialis "belonging to art," from artificium "craftsmanship."
Sâxtegi "artificial," from sâxtan "to build, to make," → structure.
Fr.: horizon artificiel
A shallow flat vessel filled with → mercury or some other viscous → liquid used in special → sextant for measuring altitudes of celestial bodies at sea in the absence of a → visible horizon.
→ artificial; → horizon.
Fr.: langue artificielle
An artificially created language system for international communication or for a specific intellectual or scientific purpose. Examples include Esperanto, computer programing languages, → symbolic logic, and → tensor analysis.
→ artificial; → language.
Fr.: lumière artificielle
Any light other than that which proceeds from the heavenly bodies.
→ artificial; → light.
Fr.: satellite artificiel
A man-made equipment that orbits around Earth or a solar system body.
→ artificial; → satellite.
Fr.: étoile artificielle
In → adaptive optics, a point source created on the sky by means of a laser beam in order to correct for the → atmospheric turbulence. A laser tuned to the wavelength of 589 nm will excite sodium atoms at an altitude of ~ 100 km in the Earth's atmosphere, producing an artificial "star."
→ artificial; → star.
Fr.: diffusion atomique
1) dogalidan; 2) dogal
Fr.: 1) bifurquer; 2) à deux branches
1) To divide into two branches.
M.L. bifurcatus, from L. → bi- "two," + furca "pitchfork; fork used in cooking," of uncertain origin.
Dogalidan, from Gilaki dogal "fork, two-branched," cf. Tabari dekal, dokkal, doqâla, from do, → two, + gal, kal "branch, part," cf. Kurd. (Kurmanji) kar "part, piece," cognate with Pers. kârd "knife," (+ *niš-) nišgarda "cobbler's knife;" Mid.Pers. kârt "knife," karēnītan, karītan "to cut," (+ *fra-) fragard "chapter, section;" Av. karət- "to cut;" Proto-Iranian *kart- "to cut;" cf. Skt. kart- "to cut;" Gk. karpos "fruit;" L. carpere "to cut, divide, pluck;" PIE base *(s)ker- "to cut;" + -idan infinitive suffix. See also → shear.
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