Achernar (Alpha Eridani)
Âxer-e nahr (#), Rudpâyân
The brightest star in the constellation → Eridanus. A → subgiant of → spectral type B5; apparent visual magnitude 0.5, about 140 → light-years distant (other names: HR 472, HD 10144). Recent interferometric observations show it to have a flattened shape imposed by fast rotation.
Achernar, from Ar. Axir an-Nahr "end of the river," from axir "end" + nahr "river".
Âxer-e nahr, from Axir an-Nahr.
1) In a → planispheric astrolabe,
the small revolving rod fixed to the center of
the goniometric scale plotted on the → front
or → back of the instrument.
Unlike the → rule,
the alidade has little vanes with holes or slots at each
end, called → pinnules, which are used as sights,
through which the observer can aim at a particular object. An index, often consisting of
the edge of the alidade itself, shows on the goniometric scales the
angle between the line of sight of the targeted object and a
predetermined axis, i.e. the vertical of the observation locality
(online museo galileo, VirtualMuseum).
M.E. allidatha, alhidade, from L. alhidada, from Ar.
Ezâdé, from Ar. al-'izâda.
Relating to an → apsis.
Fr.: mouvement apsidial
→ Rotation of the → line of apsides in the plane of the orbit in the same direction as the → revolution of the → secondary body. The major axis of the Earth's orbit rotates by 11.6 arcseconds per year.
Fr.: précession absidiale
→ advance of perihelion, → relativistic precession.
→ apsidal; → precession.
Able to be avoided or prevented.
The act of avoiding or keeping away from.
black hole candidate
nâmzad-e siyah câl (#)
Fr.: candidat trou noir
An object that seems likely to be a → black hole, but waits for more observational confirmations.
1) An applicant or suitable person for a position.
From L. candidatus "clothed in white" (reference to the white togas worn by those seeking office), from candidus "shining white," from candere "to shine," cf. Skt. cand- "to shine," candra "bright; the Moon;" PIE base *kand- "to glow, to shine."
Nâmzad, literally "nominated," from nâm, → name, + zad, p.p. of zadan "to strike" (Mid.Pers. zatan, žatan, O.Pers./Av. jan-, gan- "to strike, hit, smite, kill," Skt. han- "to strike, beat," Gk. theinein "to strike," L. fendere "to strike, push," Gmc *gundjo "war, battle;" PIE *gwhen- "to strike, kill").
dark matter candidate
nâmzad-e mâdde-ye târik (#)
Fr.: candidat matière noire
A hypothetical physical entity capable of accounting for the corresponding observed phenomena involving → dark matter. → Non-baryonic dark matter candidates include → WIMPs, → neutralinos, → axions, → gravitinos. Among → baryonic dark matter candidates can be noted ordinary and heavy → neutrinos, clouds of → neutral hydrogen gas, and compact objects.
dwarf spheroidal galaxy (dSph)
kahkašân-e korevâr-e kutulé (#)
Fr.: galaxie sphéroïdale naine
A subtype of dwarf ellipticals (→ dwarf elliptical galaxy), which are companion to the → Milky Way and other similar galaxies. The first example of such objects was discovered by Harlow Shapley (1938) in the constellation → Sculptor. 22 such galaxies are known currently to orbit the Milky Way and at least 36 exist in the → Local Group of galaxies. Nearby → galaxy clusters such as the → Virgo, → Fornax, → Centaurus, and → Coma clusters contain hundreds to thousands of individual dSph galaxies. These galaxies have very low → surface brightnesses, as low as only 1% that of the → sky background. They are also among the smallest, least luminous galaxies known. Most of the radiation from dSph galaxies is emitted by stars in the optical portion of the → electromagnetic spectrum. The lack of strong → emission lines, → infrared, or → radio emission suggests that these galaxies are generally devoid of → interstellar medium. The velocities of stars within dSph galaxies are so high that them must be disrupting. However, the bulk of mass in these galaxies might be undetected. Dynamical models that include → dark matter do adequately explain the → velocity dispersion of the stars in all dSph systems. In the most extreme cases, only 1% of the mass of the galaxy is visible. Many of the Local Group dSph galaxies show evidence for → star formation more recent than 10 Gyr.
→ dwarf; → spheroidal; → galaxy.
The River. An extensive constellation in the southern hemisphere that takes windings between 1h20 and 5h 10m right ascension, 0° to 58° south declination. Despite its size, there are not many bright stars in this constellation. Notable are → Achernar and ε Eri, a dwarf star of magnitude 4.6 and type K2, which is just 10.7 light years away. Abbreviation: Eri; genitive: Eridani.
From Gk. Eridanos, a river god, a son of Oceanus and Tethys, and father of Zeuxippe. A purely mythical river which may have been named Eridanos ("Early Burnt") from the story of Phaethon, the boy who attempted to drive the chariot of the sun, and fell flaming into the waters of this mythical river.
Rud, → river.
1) sepantruz; 2) âsudruz; 3) âsudgân
Fr.: 1); 2) férié; 3) vacances
1) A day fixed by law or custom on which ordinary business is suspended in
commemoration of some event or in honor of some person.
O.E. haligdæg, from halig "holy," → heiligenschein, + dæg, → day.
1) Sepantruz, from sepant "holy,"
→ heiligenschein, + ruz, → day.
Moon's apsidal precession
pišâyân-e habâki-ye mâng
Fr.: précession absidiale de la Lune
The → rotation of the Moon's → orbit within the → orbital plane, whereby the axes of the ellipse change direction. The Moon's → major axis makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct, or → prograde motion). The Moon's apsidal precession is a → relativistic effect, and should not be confused with its → axial procession.
→ Moon; → apsidal; → precession.
The substance which supplies the → oxygen in an → oxidation → reaction. Same as → oxydizing agent agent and → oxidizer.
Agent noun from → oxidize.
The combination of → oxygen with a substance, or the removal of → hydrogen from it.
Verbal noun of → oxidize.
Fr.: nombre d'oxydation
The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom. In other words, the charge that atom would have if the compound was composed of ions. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. Same as → oxidation state.
Fr.: état d'oxydation
Same as → oxidation number.
poloidal magnetic field
meydân-e meqnâtisi-ye qotbivâr
Fr.: champ magnétique poloÃ¯dal
1) In → protoplanetary disk models, the magnetic field
whose large-scale lines of force depart away from the → accretion disk,
in the direction of the rotation axis.
→ pole; → -oid; → magnetic field.
Having the characteristics of a sine function; same as → sine wave.