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

An arrangement of the various electrical energy sources with interconnected electrical devices.

→ electric; → network.

A follow-up community network concerned with → gamma-ray burst (GRB)s. It deals with: 1) locations of GRBs and other → transients detected by spacecraft (most in real-time while the GRB is still bursting), and 2) reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other observers. The GCN Circulars allow the GRB follow-up community to make optimum use of its limited resources (labor and telescope time) by communicating what has already been done or will soon be done.

→ gamma ray; → coordinate; → network.

Any net-like combination of elements in a system; an interconnection of several communicating entities.

O.E. net "mesh," from P.Gmc. *natjan (cf. Du. net, Swed. nät, O.H.G. nezzi, Ger. Netz, Goth. nati "net"), originally "something knotted," from PIE *ned- "to twist, knot" (cf. L. nodus "knot;" Skt. nahyati "binds, ties") + → work.

Turbast literally "joined, tied by a net," from tur "net, fishing net, snare," related to târ "thread, warp, string," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from tanidan, tan- "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch") + bast "joined, tied," from bastan, vastan "to bind, shut" (O.Pers./Av. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind).

A cardinal number, 1 plus 1. → two-color diagram; → two-photon emission.

M.E., from O.E. twa, feminine and neuter form of twegen "two," from P.Gmc. *twai (cf. O.S., O.Fris. twene, twa, O.N. tveir tvau, Du. twee, O.H.G. zwene, zwo, Ger. zwei, Goth. twai), cognate with Pers. do, as below.

Do "two," from Mid.Pers. do; Av. dva-; cf. Skt. dvi-; Gk. duo; L. duo (Fr. deux), di; Lith. dvi; O.C.S. duva; PIE base *duwo.

An astronomical → survey conducted from 1997 to 2001 of the entire sky in near-infrared J, H, and K bands (wavelengths 1.25, 1.65, and 2.17 microns respectively). The aim was to detect and characterize point sources brighter than about 1 → mJy in each band, with → signal-to-noise ratio greater than 10, using a pixel size of 2".0. Two automated 1.3-m telescopes were used, one at Mt. Hopkins, AZ, and one at CTIO, Chile. 2MASS is currently producing the following data products: 1) A digital atlas of the sky comprising approximately 4 million 8' × 16' images, having about 4" spatial resolution in each of the wavelength bands. 2) A point source catalog containing accurate positions and fluxes for 300 million stars and other unresolved objects. 3) An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and nebulae.

→ two; → micron; → all-sky survey.

In classical mechanics, the study concerned with the dynamics of an isolated system of two particles subject only to the Newtonian gravitational force between them. The problem can be separated into two single-particle problems with the following solutions. The equation of the → center of mass is governed by the equation of the same form as that for a single particle. Moreover, the motion of either particle, with respect to the other as origin, is the same as the motion with respect to a fixed origin of a single particle of → reduced mass acted on by the same internal force. See also → three-body problem, → n-body problem.

→ two; → body; → problem.

A → dynamical system consisting of two masses that interact via → central forces.

→ two; → body; → system.

A graph on which two color indices such as B-V and U-B are plotted, one along each axis, for a sample of stars or other objects, such as stars.

→ two; → color; → diagram.

A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ two; → dimensional; → flow.

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

→ two; → photon; → emission.