alpha element knee
zânu-ye bonpâr-e âlfâ
The point in the plot showing → alpha element abundances ([α/Fe]) of a galaxy as a function of the → metallicity ([Fe/H]) where the α-element abundance drops. The metallicity of the turn-over in α-element abundances is linked to the → star formation rate during the early stage of star formation in a galaxy and therefore also depends on the total mass of the system. Higher star formation efficiency leads to higher overall metallicity before the onset of → Type Ia supernova → enrichment, and thus to a knee that is located at higher [Fe/H] values.
Fr.: émission alpha
The release of → alpha particles at high velocity from an atom's nucleus as it undergoes radioactive transformation.
Fr.: émetteur d'alpha
An atomic nucleus decaying by an → alpha particle emission.
Fr.: échelle aplpha
Fr.: offset en ascension droite
A short distance from the target, in right ascension, where the telescope is pointed for various purposes.
Fr.: particule alpha
A positively charged particle emitted from the nuclei of certain atoms during radioactive disintegration. The alpha particle has an atomic weight of 4 and a positive charge equal in magnitude to 2 electronic charges; hence it is essentially a helium nucleus.
Fr.: processus α
A class of → nuclear fusion reactions by which stars convert → helium into → heavy elements. Once carbon has been created, through → triple alpha process, in a star's interior, it can then continue to fuse with further → alpha particles to produce progressively heavier elements called → alpha particles. The first stage produces oxygen, followed by neon, magnesium, silicon, sulfur, argon, calcium, titanium, chromium and iron. This is known as the → alpha ladder, with energy released as a photon at each stage.
Alphard (α Hydrae)
The only bright star in the constellation → Hydra, that has a magnitude of about 2 and a reddish color. Alphard is a giant of spectral type K3, and has a → white dwarf→ companion. Alphard is mild barium star probably contaminated by its companion before becoming a white dwarf.
Alphard, from Ar. Al-Frad ash-Shuja' "the solitary of the Serpent," from Frad "solitary" + Shuja' "a species of serpent".
Alphekka (α Coronae Borealis)
Also known as Gemma, the brightest star in Corona Borealis (visual magnitude 2.23). Alphekka is an A type dwarf lying at about 7 → light-years. Actually it has a faint Sun-like (G5 V) companion, that produces an eclipse of the primary every 17.4 days.
Alphekka, from Ar. Nayyir al-Fakkah "the bright of the broken" (ring of star), from Nayyir "bright" + fakkah "broken," from fakk "to disjoin, unloose".
Alpheratz (α Andromedae)
The brightest star in → Andromeda with a visual magnitude of 2.07. Alpheratz is a blue → subgiant star of spectral type B8 IV lying at a distance of about 97 → light-years. It is particularly remarkable because of the unusual strength of mercury and manganese absorption lines in its spectrum.
Other names for this star are Alpherat, Sirrah, or Sirah.
These names derive from Ar. As-Surrat al-Faras
1) By this or that time; previously; prior to or at some specified or
From M.E. al redy, literally "fully ready," → all, + M.E. redy "ready," from rædig, from O.E. ræde "prompt" + -ig "-y."
Pišnun, literally "prior to now," from piš-, → pre-, + Mid./Mod.Pers. nun "now, at present" (variants aknun, konun, ultimately from Proto-Ir. *hak-nun); Av. nū- "now," nūrəm "now;" O.Pers. nūram "now;" cf. Skt. nú- "now, just, but," nūnám "now, at present, indeed;" Gk. nun "now;" L. nu- "now" (in nu-dis "the day after tomorrow"); Goth. nu "now;" O.E. nu; E. now; PIE base *nu- "now."
Altair (α Aquilae)
Tâyer, Nasr-e Tâyer, Karkas-e Parandé (#)
The brightest star in → Aquila (apparent visual magnitude 0.77), and the twelfth brightest star in the sky. Altair is a whitish A7 → main sequence star. It has one of the fastest known rotational speeds, 242 km/s at the equator, compared with the Sun's about 2 km/s.
Altair, from Ar. An Nasr at-Taiir "The Flying Vulture," from Nasr "vulture" + Ta'ir "flying."
Karkas-e Parandé "The Flying Vulture" coined by Biruni (around A.D. 1000), from karkas "vulture," Av. kahrkâsa- "devourer hen," from *kahrka "hen" (Mod.Pers. kark "hen," karak "quail") + *âsa "to eat" (Mod.Pers. âš "food, soup") + Parandé "flying," from paridan "to fly" (from Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").
1) A → mounting for → telescopes
that permits both → vertical and
→ horizontal → rotation.
Altazimuth, from alt(itude) + → azimuth.
altazimuth coordinate system
râžmân-e hamârâhâ-ye farâzâ-sugân
Fr.: coordonnées azimutales
The coordinate system in which the position of a body on the → celestial sphere is described with respect to an observer's → celestial horizon and → zenith. The coordinates of a point in this system are its → altitude on the → vertical circle, and its → azimuth westward (clockwise) along the celestial horizon from the observer's south. Same as → horizon coordinate system.
Fr.: instrument altazimutal
Fr.: monture altazimutale
degargun kardan, degunidan
(v.tr.) To change or make different.
M.E. alteren, from O.Fr. altérer, from M.L. alterre, from L. alter "other," from PIE *al- "beyond" + comp. suffix -ter.
1) The act or process of altering; the state of being altered.
Verbal noun of → alter.
1) peyvâr; 2) peyvâr šodan; 3) peyvâr kardan, peyvâridan
Fr.: 1) alterné; 2, 3) alterner
1) Happening or following in turns; succeeding each other continuously.
From L. alternus "one after the other," p.p. of alternare "to do first one thing, then the other," from alternus "every other," from alter "the other".
1) Peyvâr from pey "step; after" (as in peyâpey
"successively, repeatedly") + Pers. vâr "turn (succession),
time (repetition), alternation". Compare with Skt. vâra
"one's turn, appointed time, alteration, succession".
Occuring in a successive manner. Acting or proceeding by turns. → alternating current.