An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Same as → sound pressure.

→ acoustic; → pressure.

An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields.

→ active; → region.

A type of → algorithm that dynamically achieves high → resolution in localized regions of multidimensional → numerical simulations. AMR provides a higher → accuracy solution at lower costs, through an automatically → optimal distribution of → grid points for the computation region. It relies on locally refined mesh or mesh patches to increase the resolution of an underlying coarse mesh only where needed. It can alleviate some of the complexities of the generation of high quality grid and reduce the number of → iterations of "trial-and-error" between the grid generation and solution required for tailoring the grid to the specification of a problem. Thus, it can offer orders of magnitude saving in computational and storage costs over an equivalent uniformly refined mesh. AMR was originally developed for → inviscid, → compressible flow (Berger et al., 1984, Adaptive Mesh Refinement for Hyperbolic Partial Differential Equations. J. Comp. Phy., 53, 484). It has been extended to solve → Navier-Stokes equations, time dependent problems and more. Several AMR techniques have been developed and applied to compressible flow fields to capture characteristics at the strong gradient or discontinuous regions requiring higher space resolution, such as regions involving → shock waves, vortices (→ vortex), and → wakes (see, e.g., Qingluan Xue, "Development of Adaptive Mesh Refinement Scheme and Conjugate Heat Transfer Model for Engine Simulations" (2009), Iowa State Univ., Graduate Theses and Dissertations, Paper 10678).
See also → Smoothed Particle Hydrodynamics.

→ adaptive; → mesh; → refinement.

An → adaptive optics instrument used on the → European Southern Observatory (ESO) 3.6-m telescope at La Silla. It was an upgraded version of COME-ON-PLUS, the → Very Large Telescope (VLT) adaptive optics prototype. It had 52 → actuators and performed corrections of the mirror 200 times per second. The reference → wavefront was sensed in the → visible. The observation was done in the → near-infrared (1-5 μm).

→ adaptive; → optics; → near-infrared; → system.

1) To stay attached; stick fast; cling.
2) Physics: (of two or more dissimilar substances) to be united by a molecular force acting in the area of contact (→ adhesion).

From M.Fr. adhérer or directly from L. adhaerere "to stick to," from → ad- + haerere "to stick."

Âdusidan, from intensive/nuance prefix â- + dusidan (Dehxodâ) "to stick, to adhere," maybe related to Proto-Ir. *dauc- "to sew;" Pers. duxtan, duz- "to sew."

1) The act or state of adhering; adhesion.
2) The quality of adhering; steady devotion, support, or attachment (Dictionary.com).

→ adhere + -ence, → -ance.

1) A person who follows or upholds a leader, cause, etc.; supporter; follower.
2) Sticking; clinging; adhering (Dictionary.com).

From O.Fr. adherent or directly from L. adhaerentem pr.p. of adhaerere "to stick to," → adhere.

Âdusandé, from âdusidan, → adhere.

The temperature gradient defining the → radiative equilibrium condition in a region. It is expressed as: dT/dr = (1 - 1/ γ)((T / P)(dP / dr), where T and P are temperature and pressure, dT / dr and dP / dr temperature and pressure gradients respectively, and γ = C_P / C_V. For radiative equilibrium to be stable against → convection, the actual temperature gradient must be less than the adiabatic temperature gradient, i.e. |dT /dr|_rad < |dT /dr|_ad. See also → Schwarzschild's criterion.

→ adiabatic; → temperature; → gradient.

1) To have the same views, emotions, etc.; harmonize in opinion or feeling (often followed by with).
2) To give consent; assent (often followed by to).
3) To come to one opinion or mind; come to an arrangement or understanding; arrive at a settlement.
4) To be consistent; harmonize (usually followed by with).
5) To correspond; conform; resemble (Dictionary.com).

M.E. agre, agreen, from O.Fr. agreer "to receive with favor, take pleasure in," from phrase a gré "favorably, of good will," from L. → ad- "to" + gratum "pleasing," neuter of gratus "pleasing, agreeable," from PIE root *g^wer- "to praise;" cf. Pers. gerâmi "dear, revered," from Av. gar- "to praise;" Skt. grnati "sings, praises," Lith. giriu "to praise, celebrate."

Infinitive from sâcan, → agreement.

1) The act of agreeing or of coming to a mutual arrangement.
2) The state of being in accord (Dictionary.com).

Verbal noun from → agree + → -ment.

Sâcan, from sâz-, saz, sac-, sâj-, Pers. sâz-, sâxtan "to build, prepare; to agree, be compatible; to adapt, adjust;" sazidan "to suit, fit, be worthy," sazâ "suitable, agreeing with, congruous, deserving of;" Baluchi sâc-/sâcit "to adjust, be suitable, agree;" Mid.Pers. sacitan/sazidan "to fit," sazešn "fitness," sazâg "fitting, worth;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach;" Proto-Ir. *sac- "to fit, be suitable; to prepare;" + suffix -an, → minus.

The occupation or science of cultivating the land, producing crops, and feeding, breeding, and raising livestock; farming.

M.E., from M.Fr., from L. agricultura, compound of agri cultura "cultivation of land," from agri, genitive of ager "a field" + cultura "cultivation," → culture.

Kešâvarzi "agriculture," from kešâvarz "farmer, cultivator," from kešt-varz. The first component kešt, variant kâšt, from kâštan, keštan, variants of kâridan "to cultivate, to plant;" Mid.Pers. kištan, kâridan "to sow, plant; to make furrows;" Av. kar- "to strew seed, cultivate," kāraiieiti "cultivates;" cf. Skt. kar- "to scatter, strew, pour out." The second component varz agent noun of varzidan "to labor, exercise, practise;" cf. Gk. ergon "work;" Arm. gorc "work;" Lith. verziu "tie, fasten, squeeze," vargas "need, distress;" Goth. waurkjan; O.E. wyrcan "work," wrecan "to drive, hunt, pursue;" PIE base *werg- "to do, to work."

The second brightest star of the constellation → Cygnus, with a visual magnitude of 3.0. It is a double star of strikingly different colors, with components separated by 35''. The brighter component is a K3 giant while its partner is a main-sequence B9 star. About 380 → light-years away, the two rotate around each other with a period of about 75,000 years. The main component is itself a binary system.

Albireo may be a corruption of the L. phrase ab ireo "from the rainbow," as suggested by some writers on star names. It does not mean "the hen's beak".

Menqâr-e Dajâjé "hen's beak," from Ar. Minqâr al-Dajâjah, from minqâr "beak" + dajâjah "hen".
Nok-e Mâkiyân "beak of the hen," from Mod.Pers. nok "beak" + mâkiyân "hen".

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".

1) By this or that time; previously; prior to or at some specified or implied time.
2) Now; so soon; so early (Dictionary.com).

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."

An → electric current that reverses direction of flow at regular intervals. The typical alternating current is → sinusoidal in shape. Alternating current has the advantage over → direct current in that its → voltage magnitude can be changed easily through a → transformer. Moreover, it is safer to transfer over the longer city distances and can provide more → power. The frequency of alternating current is 50 Hz (Europe) or 60 Hz (USA).

→ alternating; → current.

The → SI unit of → electric current; symbol A. It is defined by taking the fixed numerical value of the → elementary charge, e, to be 1.602 176 634 × 10^-19 when expressed in the unit → coulomb (C), which is equal to A s, where the → second (s) is defined in terms of Δν_Cs.

Named after the French physicist and mathematician André-Marie Ampère (1775-1836), one of the pioneers in studying electricity, who laid the foundation of electromagnetic theory.

One of the basic relations between → electricity and → magnetism, stating quantitatively the relation of a → magnetic field to the → electric current or changing electric field that produces it. Ampere's law states that the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path. Also known as Ampère's theorem, Ampère's circuital law.

→ ampere; → law.

The angle between the reflected ray and the normal to the reflecting surface.

→ angle; → reflection.

The angle between the direction in which a ray is refracted and the normal to the refracting surface.

→ angle; → refraction.

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.