Fr.: cercle d'égale altitude
A circle on the celestial sphere that has equal altitude over the Earth's surface and lies parallel to the horizon. Also called almucantar, circle of altitude, parallel of altitude.
A silver-white, malleable and ductile metal, symbol Al. → Atomic number 13; → atomic weight 26.98154; → melting point 660.37°C; → boiling point 2,467°C; → specific gravity 2.6989 at 20°C. Its electric → conductivity is comparable with that of copper, so that being much lighter it is used extensively for transmission lines. The metal and its → alloys have strength with lightness. The → reflectivity of aluminium is high and it is therefore used broadly for coating → mirrors (→ aluminization). Aluminium occurs widely in clays; it is extracted mainly from bauxite. It has several → radioactive isotopes with half-lives from 2.3 sec (23Al) to 6.56 min (29Al). When aluminium is bombarded with → alpha particles, its atoms first turn into radioactive → phosphorus, then into → silicon. This occurs naturally in → massive stars.
The name of the chemical element, was coined by Sir Humphry Davy (1778-1829), from L. alumen "alum; bitter salt," akin to Gk. aludoimos "bitter" and Eng. ale. Davy originally called it alumium (1808), then modified this to aluminum, which remains the U.S. word, but British editors in 1812 further amended it to aluminium. In 1825, the Danish physicist Hans Christian Oersted (1777-1851) isolated impure aluminium. The pure metal was first isolated by the German chemist Friedrich Wöhler (1800-1882) in 1827.
âluminiom andudan (#)
Âluminiom andudan, from âluminiom + andudan "to incrustate, plaster, cover over."
âluminiom andud (#)
The process by which the coating of aluminium is deposited on a telescope mirror.
Verbal noun of → aluminize.
AM CVn star
setâre-ye AM Sagân-e Tâzi
Fr.: étoile AM CVn
A → binary system that has very short orbital period (less than one hour) and helium dominated spectrum. The prototype, AM Canum Venaticorum, with a period of 17 minutes, was discovered in 1967. AM CVn stars are → semidetached binary systems in which → accretion is going on. The → donor star is hydrogen deficient and the → accretor is usually a → white dwarf. To fit within their → Roche lobes, the donor stars must be dense, suggesting they may be → degenerate too. It is at present thought that AM CVn stars represent three possible evolutionary phases in 1) → double white dwarf systems, 2) white dwarf and → helium star binaries, and 3) → cataclysmic variables with evolved donors. For a review see G. Nelemans 2005, astro-ph/0409676.
Fr.: AM Herculis
A → red dwarf variable star located in the constellation → Hercules. AM Herculis usually remains in its "high" state (V ~ 13 mag), but from time to time it drops into a "low" state (V> 15 mag) that may last weeks or months. Originally classified as an irregular variable and associated with the X-ray source 3U 1809+50, AM Her was discovered in 1976 to be a short-period → binary system (3.1 hour orbital period) related to the → cataclysmic variables. It is in fact an → interacting binary in which a red dwarf (M4 V) loses mass to a → white dwarf primary star. The white dwarf has a very strong magnetic field (B ~ 2 × 108 G) and rotates synchronously with the orbit. The magnetic field constrains the → mass loss from the secondary star to flow along a stream directly onto the white dwarf rather than into an → accretion disk as in the nonmagnetic cataclysmic variables. The optical spectrum shows strong emission lines of H, He I, and He II, along with weaker lines of other ions such as N III, C III, C II, and Ca II, all showing large velocity variations. → TiO bands from the M4 V secondary star are detected when the system is in its "low" state. AM Her is the class prototype of the → polars (see, e.g., Hutchings et al. 2002, AJ 123, 2841).
AM, letters of alphabet used in variable star designations; → Hercules.
Fr.: étoile Am
A chemically peculiar A- or early F-type star showing an overabundance of → heavy elements and an underabundance of calcium and scandium. An Am star cannot receive a unique spectral type, as different methods (using the metallic lines, the hydrogen Balmer lines, and the calcium Ca II K-lines) yield three different spectral types. Contrarily to Ap stars, Am stars do not have significant external magnetic fields. Their rotational velocities are about 100-120 km s-1 smaller than those of → Ap stars.
Amalthea [Jupiter V]
The third of Jupiter's known satellites orbiting at about 181,300 km from Jupiter with a period of about 12h. A mean diameter of 189 km makes it the fifth largest satellite of Jupiter. Amalthea was discovered by E. Barnard in 1892.
Amalthea, in Gk. mythology, the goat that suckled Zeus after his mother had him sent to Crete so his father would not eat him.
1) To collect into a mass or pile; → accumulate.
Anbâštan, anbârdan "to fill, to replete," from Mid.Pers. hambāridan "to fill;" from Proto-Iranian *ham-par-, from prefix ham-, → com-, + par- "to fill;" cf. Av. par- "to fill," parav-, pauru-, pouru- "full, much, many;" O.Pers. paru- "much, many;" Mid.Pers. purr "full;" Mod.Pers. por "full, much, very;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full.
From Fr. amateur "lover of, one who has a taste for (something)," from L. amator "lover," from amare "to love."
Dustkâr, a variant of dustâr, dustdâr "he who likes, lover, supporter," from dust "friend, lover" + kâr "occupation, → work."
axtaršenâs-e dustkâr (#)
Fr.: astronome amateur
axtaršenâsi-ye dustkâr (#)
Fr.: astronomie amateur
The astronomical activities carried out by → amateur astronomers.
Fr.: ère amazonienne
The current geologic era on Mars that began around 2 billion to 3 billion years ago. It is characterized by lower geologic activity such as volcanism and only occasional releases of underground water. A dry environment with a very thin atmosphere in which water can only exist as a solid or a gas, not as a liquid. → Noachian era; → Hesperian era.
Named for the young lava-covered plains called Amazonia Planitia. → era.
A hard translucent yellow, orange, or brownish-yellow fossil resin. Amber becomes negatively charged when rubbed with wool, because it attracts negative charges (electrons) and will take them from wool.
M.E. ambre, from O.Fr., from L. ambra, ambar, from Ar. 'anbar "ambergris, amber," from Mid.Pers. ambar, → ambergris.
Kahrobâ, from kah "straw" + robâ "attractor." The first component kah, kâh "straw, hay," from Mid.Pers. kâh "chaff, straw;" cf. Pali kattha- "a piece of wood;" Skt. kastha- "stick;" Gk. klados "twig;" O.Ir. caill "wood;" P.Gmc. *khulto-; Ger. Holz "wood;" E. holt; PIE *kldo-. The second component robâ, from robudan "to attract, to grab, rob;" Av. urūpaiieinti "to cause racking pain(?);" cf. Skt. rup- "to suffer from abdominal pain," rurupas "to cause violent pain," ropaná- "causing racking pain," rópi- "racking pain;" L. rumpere "to break;" O.E. reofan "to break, tear." In Arabic kahrobâ, a loanword from Persian, is used as equivalent for electricity.
Fr.: ambre gris
A wax-like, ash-colored, strongly scent substance present in the intestines of → whales and found in seas or cast ashore. Used in perfumery.
Anbar "ambergris," from Mid.Pers. ambar.
Both, on both sides.
L. ambi "around, about," akin to Gk. amphi "around, about," Skt. abhi "on both sides," Av. aibi, aiwi, O.Pers. aiby "to, against, in addition to," Mid.Pers. aw-, ab-, Mod.Pers. af- (as in afzudan "to increase, add," afruxtan "to inflame, kindle, blaze," afqân "lamentation, groaning, cires for help"); O.H.G. umbi, O.E. ymb(e); PIE *ambhi- "around".
Ubâ- from O.Pers./Av. uba- (variants uva-, ava-, va-) "both," Skt. ubha "both," PIE *ubho(u); cf. Gk. ampho, L. ambo, Goth. bai, O.H.G. beide, Slav. oba, Lith. abhu.
The quality of state of being → ambiguous.
Having more than one possible interpretation or meaning.
From L. ambiguus "having double meaning; doubtful," from ambigere "to be uncertain," from → ambi- "both; around" + agere "to drive, lead," → act; cf. Av. az- "to drive, lead;" Pers. niyâz "need, want, misery,"
1) Applying equally to both positive and negative ions.
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.