An Etymological Dictionary of Astronomy and Astrophysics
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The effective value of the → Eddington parameter in a non-homogeneous system (porous opacity).

→ effective; → Eddington limit; → parameter.

In cosmology, a → dimensionless parameter introduced by the → equation of state representing the ratio of the pressure to the energy density of a fluid, such as the → dark energy: w = p/ρ. The → deceleration or → acceleration of an → expanding Universe depends on this parameter (→ accelerating Universe). A number of numerical values of this parameter are as follows: for the → cosmological constant: w = -1, for → non-relativistic matter (present-day → baryons): w = 0, and for → relativistic matter (photons, neutrinos): w = +1/3. Together with Ω(dark energy) and Ω(matter), w provides a three-parameter description of the dark energy. The simplest parametrization of the dark energy is w = constant, although w might depend on → redshift.

→ equation; → state; → parameter.

A program that can run on a → computer. It uses an → executable file.

→ executable; → program.

A → scale factor that relates the size of the Universe R = R(t) at time t to the size of the Universe R₀ = R(t₀) at time t₀ by R = aR₀. The expansion parameter represents the history of expansion of the Universe.

→ expansion; → parameter.

A schematic representation, in quantum electrodynamics and quantum chromodynamics, of the way elementary particles like electrons and protons interact with each other by exchanging photons. Use of Feynman diagrams can greatly reduce the amount of computation involved in calculating a rate or cross section of a physical process.

After the American physicist Richard P. Feynman (1918-1988), Nobel prize 1965; → diagram.

One of the three quantities (k, α, and δ) which are used in the → radiation-driven wind theory to express the radiation pressure due to spectral lines. These coefficients parametrize the radiation acceleration as: g_rad≅ k(dv/dr)^αg_e, where g_e = σ_eL/4πcR_*² is the radiative acceleration by electron scattering. The parameter k is dependent on the number of lines that produce the radiation pressure. The parameter α depends on the optical depth of the driving lines and varies between 0 (optically thin) and 1 (optically thick). The parameter δ describes the dependence of k on the density with k ≅ ρ^δ. The velocity law of radiation-driven winds depends on α and δ, but not on k. The → mass loss rate depends on k, α, and δ (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269 and references therein).

→ force; → multiplier; → parameter.

1) A border or case for enclosing a picture, mirror, etc.; a structure for admitting or enclosing something.
2) One of the successive pictures on a roll of movie film or videotape.
3) In computers, the information or image on a screen or monitor at any one time.

Frame, from M.E. verb framen "to prepare (timber)," from O.E. framian "to avail, profit."; cf. O.H.G. (gi)framon "to do."

1) Cârcub "frame," from câr, contraction of cahâr "four" (→ four) + cub "stick, satff, beam," Mid.Pers. côp "wood, stick." 2) Tasvirak from Ar. tasvir "image" + -ak suffix of relation and similarity (as in poštak, dastak, nâxonak), → fibril.

The alteration in the → free fall motion of a test → mass in the presence of a massive → rotating object, as compared to the identical case of a non-rotating object. This dragging of → inertial frames is predicted by → general relativity. Also called → Lense-Thirring effect.

→ frame; → drag.

The number of times per second that the frame is scanned in television. Also known as picture frequency.

→ frame; → frequency.

A set of axes to which positions and motions in a system can be referred.

→ frame; → reference.

The process of adjusting a television picture to a desired position in the direction of progression.

From → frame + → -ing.

Cârcubeš, verbal noun of cârcubidan, from cârcub→ frame.

One of the parameters that characterize atmospheric → seeing. It is the diameter of the largest aperture that can be used before → turbulence starts to degrade the image quality. As the turbulence gets stronger, the Fried parameter, denoted r₀, becomes smaller. The Fried parameter is wavelength dependent: r₀ ∝ λ^6/5. On best astronomical mountain tops it ranges between 20 and 30 cm for λ = 5000 A.

Named after David L. Fried, who defined the parameter 10 1966; → parameter.

Same as → inertial reference frame.

→ Galilean; → reference; → frame.

A unit of mass equal to one thousandth of a kilogram.

From Fr. gramme, from L.L. gramma "small weight," from Gk. gramma "small weight," originally "letter of the alphabet," from stem of graphein "to draw, write."

Geram, loanword from Fr. gramme, as above.

1) The study of the way the sentences of a language are constructed; → morphology and → syntax.
2) These features or constructions themselves (Dictionary.com).

M.E. gramarye, from O.Fr. gramaire "grammar; learning," especially Latin and philology, an "irregular semi-popular adoption" of L. grammatica, from Gk. grammatike (tekhne) "(art) of letters" with a sense of both philology and literature, from grammatikos "pertaining to or versed in letters or learning," from gramma "letter," → -gram.

Dastur-e zabân, literally "language rule," from dastur "rule; mandate, command; religious authority (of the Zoroastrians);" Mid.Pers. dast "able, capable;" Av. danh- "to teach, instruct;" cf. Skt. dams- "to show or teach wonderful skills, perform wise;" Gk. didasko "I learn;" PIE *dens- "to become skilfull; to teach, instruct" (Cheung 2007); + zabân, → language.

A specialist or expert in grammar.

From O.Fr. gramairien "learned man, person who knows Latin," agent noun from grammaire, → grammar.

Zabân-dasturdân, literally "knower of grammar," from zabân-dastur→ grammar + dân agent noun and present stem of dânestan, → know.

Of or relating to → grammar; conforming to standard usage.

From M.Fr. grammatical and directly from L. grammaticalis "of a scholar," from grammaticus "pertaining to → grammar."

Dastur-e zabâni, zabân-dasturidastur-e zabân, zabân-dastur, → grammar.

An inflectional category, basically pertaing to nouns and pronoun, which marks their relationship with other parts of the sentence. sentence. → accusative case, → nominative case, → genitive case, → dative case, → ablative case, → vocative case, → imperative case.

→ grammatical; → case.

Same as → Hertzsprung-Russell diagram.

Short for → Hertzsprung-Russell diagram.

A record made by a → heliograph.

→ helio-; + → -gram.