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

The difference in → right ascension between the → Sun and the → Moon, measured in degrees.

→ arc; → separation.

The cyclic process in which interstellar matter is incorporated into newly formed stars, where it undergoes nuclear processing, is thus enriched with heavier elements, and then returns into the interstellar medium through supernova explosion or stellar winds to be used in the formation of a newer generation of stars.

Astration, from astrate, from astr-, → astro-, + noun-forming suffix -ation.

Setâreš, from setâridan (from setâré "star" + verb-making suffix -idan) + noun-builder -eš.

Of a body traveling from A to B, the change of → velocity divided by the time interval: ā = (v₂ - v₁) / (t₂ - t₁).

→ average; → acceleration.

The → baryon number compared with the number of photons in the → Universe. The baryon-photon ratio can be estimated in a simple way. The → energy density associated with → blackbody radiation of → temperature  T is aT⁴, and the mean energy per photon is ~kT. Therefore, the number density of blackbody photons for T = 2.7 K is: n_γ = aT⁴/kT = 3.7 x 10² photons cm^-3, where a = 7.6 x 10^-15 erg cm^-3 K^-4 (→ radiation density constant) and k = 1.38 x 10^-16 erg K^-1 (→ Boltzmann's constant). The number density of baryons can be expressed by ρ_m/m_p, where ρ_m is the mass density of the Universe and m_p is the mass of the → proton (1.66 x 10^-24 g). → CMB measurements show that the baryonic mean density is ρ_m = 4.2 x 10^-31 g cm^-3 (roughly 5% of the → critical density). This leads to the value of ~ 2 x 10^-7 for the number density of baryons. Thus, the baryon/photon ratio is approximately equal to η = n_b/n_γ = 2 x 10^-7/3.7 x 10² ~ 5 x 10^-10. In other words, for each baryon in the Universe there is 10¹⁰ photons. This estimate is in agreement with the precise value of the baryon-photon ratio 6.14 x 10^-10 derived with the → WMAP. Since the photon number and the baryon number are conserved, the baryon-photon ratio stays constant as the Universe expands.

→ baryon; → photon; → ratio.

A mathematical operation that combines two numbers, quantities, sets, etc., to give a third. For example, multiplication of two numbers is a binary operation.
A binary operation * on a set S is → commutative if a * b = b * a for all a, b∈ S.
A binary operation * on a set S is → associative if (a * b) * c = a * (b * c) for all a, b, c∈ S.

→ binary; → operation.

A quantity used to describe a → radionuclide that has more than one → decay mode. For a particular decay mode, the ratio of the number of atoms decaying by that decay mode to the number decaying in total: BR_i = k_i/(k₁ + k₂ + ...) = k_i/k, where k is → decay constant.

→ branching; → ratio.

1) The act or process of calibrating or the state of being calibrated.
2) A set of graduations that show positions or values.

Calibration, noun from → calibrate.

Kabizeš, noun from kabizidan, → calibrate.

An empirical curve obtained through appropriate exposures in order to determine the instrument's response. For example, a curve allowing the conversion of relative intensities of an observed object into absolute fluxes, or a curve relating the detector's pixel positions to wavelengths.

→ calibration; → curve.

A systematic error in the constant values to be applied to a measuring instrument.

→ calibration; → error.

Irang, → error; kabizeš, → calibration.

An exposure obtained with an instrument mounted on the telescope using an artificial illuminating source in order to calibrate the instrument.

→ calibration; → exposure.

Nurdâd, → exposure; kabizeš, → calibration.

A lamp used for instrument calibration, such as an internal He-Ar arc for wavelength calibration or an external source of light placed in the telescope dome for flat-field exposures.

→ calibration; lamp, from O.Fr. lampe, L. lampas, from Gk. lampas "torch, lamp, light, meteor," from lampein "to shine."

Kabizeš, → calibration; lâmp, from Fr., as above.

Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v²/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.

→ centrifugal; → acceleration.

The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: a_c = v²/r = rω². According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.

→ centripetal; → acceleration.

The physical processes that can cause certain elements to migrate in a → stellar atmosphere. These processes are thought to be important in creating the chemical peculiarities seen in → Am stars and → Ap stars.

→ chemical; → separation.

A defect in a lens that causes it to concentrate the various colors in a beam of light at various point, thus producing color fringes.

→ chromatic; → aberration.

The act or process of working with another or others on a joint project.

From Fr. collaboration, noun of action from L. collaborare from → com- "with" + labore "to work."

Hamkâri, from ham-, → com-, + kâr, → work, + -i verbal noun suffix.

1) The act of concentrating or the state of being concentrated.
2) Chemistry: A measure of the amount of dissolved substance contained per unit of volume in a solution.

Verbal noun from → concentrate.

A body comprising independent organizations that cooperate for a common purpose.

→ com-; → federation.

General: Arrangement of parts or elements in a composite object.
Physics: The distribution of electrons in the various atomic orbital and energy levels.

L.L. configuration, configuratio "similar formation," from L. configurare "to form from or after," from → com- + figurare "to form," from figura "figure."

Hampeykareš (verbal noun from hampeykaridan), from ham-, → com-, + peykar "figure, form, mould, body" + noun suffix -eš. Peykar from Mid.Pers. pahikar "picture, image," from O.Pers. patikara- "picture, (sculpted) likeness," from patiy "against" (Av. paiti, Skt. prati, Gk. poti/proti) + kara- "doer, maker," from kar- "to do, make, build," Av. kar-, Skt.. kr-; cf. Skt. pratikrti- "an image, likeness, model; counterpart."

1) The act of conglomerating; the state of being conglomerated.
2) a cohering mass; cluster (Dictionary.com).

Verbal noun of → conglomerate.