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

1) The surface surrounding a → black hole with the property that any light ray emitted inside it cannot escape to the outer space because of the strength of the → gravitational field. The radius of the event horizon is called the → Schwarzschild radius. See also → photon sphere.
2) For an observer A at the instant t₀, the surface in the → space-time that divides the collection of all events into two non-empty classes: those events that have been, are being, or will be observed by A, and those that A has never observed and will never be able to observe (J. Plebanski, A. Krasinski, 2006, An Introduction to General Relativity and Cosmology, Cambridge Univ. Press).

→ event; → horizon.

An international collaboration using a → very-long-baseline interferometry (VLBI) array comprising millimeter- and → submillimeter- wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, the EHT → angular resolution (λ/D) is ~25 μas (→ micro- → arcseconds), which is sufficient to resolve nearby → supermassive black hole candidates on spatial and temporal scales that correspond to their → event horizons. EHT observations toward the elliptical → galaxy M87 succeeded in obtaining the first ever image of its supermassive black hole (EHT Collaboration, 2019, ApJL 875, L1-L6). The telescopes contributing to this result were ALMA, APEX, the IRAM 30-m telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope. Petabytes of raw data from the telescopes were combined by highly specialized supercomputers hosted by the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory. The construction of the EHT and the M87 black hole observation result from decades of observational, technical, and theoretical work in close collaboration by researchers from around the world. Thirteen partner institutions worked together to create the EHT, using both pre-existing infrastructure and support from a variety of agencies. Key funding was provided by the US National Science Foundation (NSF), the EU's European Research Council (ERC), and funding agencies in East Asia.

→ event; → horizon; → telescope.

Same as → accelerating Universe.

→ expand; → Universe.

That which tends to prove or disprove something; something that makes plain or clear.

Noun form of → evident.

Âvišé, from âviš, → evident + noun suffix -é, Mid.Pers. -ak/-ag.

Plain or clear to the sight or understanding.

From L. evidentem (nom. evidens) "perceptible, obvious," from → ex- "fully, out of" + videntem (nom. videns), pr.p. of videre "to see," from PIE base *weid- "to know, to see;" cf. Mod.Pers. bin- "to see" (present stem of didan); Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know;" Gk. oida "I know," idein "to see;" O.E. witan "to know;" Goth. weitan "to see;" E. wise; Ger. wissen "to know;" Lith. vysti "to see;" Rus. videt' "to see," vest' "news."

Âviš, from Av. āviš, āuuiš "evidently, before the eyes," āuuišiia- "manifest;" Mid.Pers. âškârâg "manifest;" Mod.Pers. âškâr (Proto-Iranian *āuiš-kâr); Arm. loanword from Iranian aškaray "open, not hidden;" cf. Skt. āvis "evidently, before the eyes;" O.C.S. (j)avé "manifest, known" (loanword from Iranian); L. audire "to hear;" Gk. aisthanesthai "to feel."

The act or fact of evoking.

Verbal noun of → evoke.

1) To call up or produce (memories, feelings, etc.).
2) To elicit or draw forth (Dictionary.com).

From Fr. évoquer or directly from L. evocare "call out, rouse, summon," from → ex- "out" + vocare "to call," → voice .

Zâvacidan, from zâ-, → ex-, + vacidan "to call," → convoke.

Any process of formation or growth; development; a process of gradual, progressive change; a product of such development; something evolved.
Astro.: A continuous and progressive change according to certain laws and by means of acting physical forces.
Biology: A process of development in which a living organism, through major environmental changes, becomes more and more complex by the differentiation of its parts.

Verbal noun of → evolve.

Of, pertaining to, or in accordance with a theory of evolution.

Adjective of → evolution.

The stellar mass based on → effective temperature and → luminosity, as derived from → evolutionary tracks.

→ evolutionary; → mass.

A model, based on theoretical calculations, which predicts the behavior of an astronomical entity (stars, galaxies, Universe) over time.

→ evolutionary; → model.

A particular step or phase in the evolution of an astronomical object.

→ evolutionary; → stage.

The characteristic time it takes an evolving astronomical object to pass from a step to another.

→ evolutionary; → time scale.

In a theoretical → Hertzsprung-Russell diagram, the path taken by an evolving star.

→ evolutionary; → track.

To come forth gradually into being; undergo evolution.
Astro.: To change with time by the action of varying physical conditions.
Biology: To develop by a process of evolution to a different adaptive state or condition.

L. evolvere "to unroll, open, unfold," from → ex- "out" + volvere "to roll, turn, twist;" PIE base *wel- "to turn, revolve;" cf. Skt. valate "turns round;" Gk. eilein "to turn, squeeze," helix "spiral object;" O.H.G. walzan "to roll, waltz;" Lith. valtis "twine, net," apvalus "round;" O.E. wealwian "to roll (in mud);" Welsh olwyn "wheel."

Fargaštan, fargašt kardan, from fargašt, from far- "forward" (Mid.Pers. fra- "forward, before; much; around;" O.Pers. fra- "forward, forth;" Av. frā, fərā-, fra- "forward, forth; excessive;" cf. Skt. prá- "before; forward, in fron;" Gk. pro "before, in front of;" L. pro "on behalf of, in place of, before, for;" PIE *pro-) + gašt, present stem of gaštan, gardidan "to change; to turn" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" cf. Skt. vartati; L. vertere; O.H.G. werden "to become;" PIE *werto, *wer-).

A space project, initially → LISA, consisting of a configuration of three satellites, aimed to detect low frequency → gravitational waves that cannot be measured by ground-based detectors. The detection range will be from about 0.1 milliHz to 1 Hz. One "mother" and two "daughter" spacecrafts will be brought into an orbit around the Sun, which is similar to the Earth's orbit. The satellites will fly in a near-equilateral triangle formation, with a constant distance of one million km between, following the Earth along its orbit at a distance of around 50 million km. The mother spacecrafts carries two and each of the daughter spacecraft carry one free-flying → test masses that will be kept as far as possible free of external disturbances. The mutual distances of the test masses from satellite to satellite will be measured by means of high-precision, → Michelson-like laser → interferometry. In this way, the extremely small distance variations between the test masses of two satellites can be detected which are caused by the passages of a gravitational waves. The required measurement accuracy of the distances amounts to typically 1/100 of the diameter of a hydrogen atom (10^-12 m) at a distance of two million km.

→ evolve; → laser; → interferometer; → space; → antenna.

A star that has left the → main sequence.

→ evolve; → star.

A female sheep, especially when fully mature.

M.E.; O.E. eowu, ewe "female sheep;" cognate with O.H.G. ou, ouwi, Du. ooi, L. ovis, Gk. ois, ois, Skt. avi; PIE *owi- "sheep."

Miš, from Mid.Pers. mêš "sheep, ewe;" Av. maeša- "sheep, ewe;" cf. Skt. mesa-, mesi "sheep, ewe."

A classical → T Tauri star, and the EXor prototype, subject to sporadic outbursts. It remains at about V = 13.2 mag for extended periods to brighten to as much as V = 8.4 mag (1955-1956). When EX Lupi is at minimum, it resembles a classical T Tauri star of type M0. At outburst this spectrum is veiled by a hot continuum, the equivalent widths of the optical-region emission lines decrease, and reverse P Cygni absorption components appear at the higher Balmer lines. The outbursts are believed to be due to episodic infall onto the M0 star. → FU Orionis objects.

E and X, letters of alphabet; Lupi, genitive of → Lupus.

Prefix meaning "out of, outside; from," but also "upwards, completely, deprive of, without."

From M.E., from O.Fr., from L. ex- "out of, from," akin to Gk. ex, ek "out of;" Av. uz-, us-, see below; from PIE base *eghs "out" (cf. Gaul. ex-; O.Ir. ess-; O.C.S. izu; Rus. iz).

Pers. os- (variants zo-, so-), from Mid.Pers. us-, uz-; Av. uz-, us- "out of, outside, from;" O.Pers. ud- (ud-apatatā "to rise up, rebel"), also Pers. preposition az "from; of; out of," prefixes zo- (in zodudan "to polish, clean;" Mid.Pers. uzdâtan; Av. uzdā-, from uz- + dā- "to make, create"), âz- (âzmâyeš, → experiment), haz- (haziné "cost, expenditure;" Mid.Pers. uzên, uzênak, from *uz-ayana- "going out;" Av. us- + ay- "to go," → assembly), es- (eskane "chisel"); PIE *ud- "up, out," cf. Skt. úd "up, away, out;" O.E. ūt "out;" E. out; O.H.G. ūz "out;" Ger. aus; Russ. vy- "out."
Borun "out, the outside" (Mid.Pers. bêron, from bê "outside, out, away" + rôn "side, direction;" Av. ravan- "(course of a) river").