An Etymological Dictionary of Astronomy and Astrophysics

To determine or set the value or amount of; to judge or determine the significance, worth, or quality of.

See also: Verbal form of → evaluation.

An act or instance of evaluating; to examine and judge carefully.

Etymology (EN): From Fr. évaluer “to find the value of,” from → ex- “out”

• value “worth, value,” p.p. of valoir “be worth,” from L. valere “be strong, be of value;” PIE base *wal- “to be strong.”

Etymology (PE): Arzyâbi, from arz “value” + yâbi “finding.” The first component arz, present stem of arzidan “to be worth,” arzân “worthy; of small value, cheap,” arj “esteem, honour, price, worth;” Mid.Pers. arz “value, worth,” arzidan “be worth,”
arzân “valuable;” Av. arəjaiti “is worth,” arəja- “valuable,” arəg- “to be worth;” cf. Skt. arh- “to be worth, to earn,” árhant- “worthy person;” Gk. alphanein “to bring in as profit,” alphein “to ear, obtain;” Lith. algà “salary, pay;” PIE base *alg^wh- “to earn; price, value.” The second component yâbi, verbal noun of yâftan, yâbidan “to find, discover; to obtain, acquire;” Mid.Pers. ayâftan, ayâpênitan “to reach, attain;” Manichean Mid.Pers. ‘y’b “to attain;” Parthian, Sogdian (+ *pati-) pty’b “to reach, obtain;” Av. ap- “to reach, overtake,” apayeiti “achieved, reached;” Skt. âp- “to reach, gain,”
âpnoti “reaches, gains;” Gk. hapto, haptomai “to touch, cling to, adhere to;” L. apiscor “touch, reach;” PIE base *ap- “to take, reach.”

To disappear gradually.

See also: → vanish.

Tending to → vanish gradually.

See also: Verbal adj. from → evanesce.

A wave whose → amplitude → decreases → exponentially
with distance from the → interface at which it is formed. Evanescent waves are formed when → sinusoidal
waves are internally reflected off an interface at an angle greater than the → critical angle so that → total internal reflection occurs.

See also: → evanescent; → wave.

(v.intr.) To change from liquid state into vapor; (v.tr.) To convert into a gaseous state or vapor.

See also: Verbal form of → evaporation.

The physical process by which a liquid is transformed to the gaseous state, usually by means of heat; the opposite of → condensation. Also called vaporization.

Etymology (EN): From L. evaporationem (nom. evaporatio), from evaporare “to disperse in vapor,” from → ex- “out”

• → vapor “steam.”

Etymology (PE): Boxârš, verbal noun of boxâridan “to evaporate,” from boxâr, → vapor.

A periodic perturbation in the motion of the → Moon caused by the variation in the gravitational pull of the Sun, which causes a change in the → eccentricity of the Moon’s orbit during its monthly revolution. As a result, the Moon’s → ecliptic longitude oscillates with a amplitude of ± 1°16’ during a period of about 31.8 days.

Etymology (EN): From L. evection- “carrying away, going upwards, flight,” from evect(us) p.p. of evehere “to carry forth, move forth,” from e-, → ex- + vehere “to carry,” cognate with Av. vaz- “to carry, move,” as below.

Etymology (PE): Osbaz “carrying away,” from os-, → ex-,

• *baz “to carry,” ultimately from Proto-Ir. *uaz- “to carry, drive;” from which Av. vaz- “to move, carry, drive (a chariot),” vazaiti “to lead;” Kurd. (Kurmanji) bazin/baz- “to run;” Mod./Mid.Pers. bazidan, vazidan “to blow (as the wind),” parvâz, → flight; cf. Skt. vah- “to ride, drive, transport;” Gk. oxos “carriage;”
  L. vehere “to carry;” Lith. veži “I ride;” O.H.G. wegan “to move, carry;” PIE base *wegh- “to go, carry, drive.” See also:
  → advection; → convection.

A classical variable which does not change upon spatial inversion, such as time, energy, angular momentum and so on. → odd parity.

Etymology (EN): Even, from O.E. efen “level; equal,” from P.Gmc. *ebnaz (cf. Ger. eben; Goth. ibns); → parity.

Etymology (PE): Hamâli, → parity; zowj “pair, couple; an even number,” from Ar.

The latter part of the → day and early part of the → night. Not an astronomical term proper. → evening star.

Etymology (EN): From O.E. verb æfnung “to grow toward evening,” from æfnian “to become evening,” from æfen “evening,” from P.Gmc. *æbando- (cf. O.H.G. aband, Ger. abend).

Etymology (PE): Ivâr “evening” (Lori, Laki êvâra; Borujerdi ivâra; Kurd. ewâra); Mid.Pers. êwârak “evening,” ultimately from Proto-Ir. *upa-ayara- “end of the day,” from *upa- “up, on,” + *ayara- “day;” cf. Av. ayar- (aiiar-) “day;” Shughni, Roshani, Bartangi prefixed (*api-) biyôr, Sariqoli biyur “yesterday;” PIE *ayer- “day, morning;” cf. Gk. eerios “at breakfast,” ariston “breakfast;” Du. eer, Ger. eher “earlier;” E. ere “soon, before (in time).”

Any bright → planet, often → Venus, seen low in the western sky after → sunset. → Hesperus.

See also: → evening; → dusk; → star.

1. General: Something that happens or is regarded as happening; an occurrence, especially one of some importance.
   

2. Einstein’s relativity: An occurrence in the → space-time continuum referenced by three spatial coordinates and a complementary temporal ordinate. → world line; → space-time diagram.
   

3. Statistics: A subset of the → sample space.

Etymology (EN): From M.Fr. event, from L. eventus “occurrence, issue,” from evenire “to come out, happen, result,” from → ex- “out” + venire “to come,” from PIE base *gwem- “to go, come;” cf. Mod/Mid.Pers. gâm “step, pace;” O.Pers. gam- “to come; to go;” Av. gam- “to come; to go,” jamaiti “goes;” Mod.Pers. âmadan “to come;” Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come.

Etymology (PE): Ruydâd, noun from ruy dâdan “to occur, happen,” originally “to appear,” from ruy “face; aspect; appearance” (Mid.Pers. rôy, rôdh “face;” Av. raoδa- “growth,” in plural “appearance,” from raod- “to grow, sprout, shoot;” cf. Skt. róha- “rising, height”) + dâdan “to give; to command” (Mid.Pers. dâdan “to give;” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” cf. Skt. dadáti “he gives;” Gk. didomi “I give;” L. dare “to give, offer,” facere to make;" PIE base *do- to give").

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).

See also: → 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.

See also: → event; → horizon; → telescope.

Same as → accelerating Universe.

See also: → expand; → Universe.

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

Etymology (EN): Noun form of → evident.

Etymology (PE): Âvišé, from âviš, → evident

• noun suffix -é, Mid.Pers. -ak/-ag.

Plain or clear to the sight or understanding.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: Verbal noun of → evoke.

1. To call up or produce (memories, feelings, etc.).
   

2. To elicit or draw forth (Dictionary.com).

Etymology (EN): From Fr. évoquer or directly from L. evocare “call out, rouse, summon,” from → ex- “out” + vocare “to call,” → voice .

Etymology (PE): 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.

See also: Verbal noun of → evolve.

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

See also: Adjective of → evolution.

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

See also: → evolutionary; → mass.

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

See also: → evolutionary; → model.

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

See also: → evolutionary; → stage.

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

See also: → evolutionary; → time scale.

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

See also: → 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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → evolve; → laser; → interferometer; → space; → antenna.

A star that has left the → main sequence.

See also: → evolve; → star.