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

An expanding → equatorial → disk or → torus of material ejected by a star. The phenomenon may result from a stellar → merger or an increase in its rate of → rotation or → stellar winds. Contrasted with → accretion disk.

→ excretion; → disk.

Math: A theorem that asserts the existence of at least one object, such as the → solution to a → problem or → equation.

→ existence; → theorem.

1) The outermost portion of the Earth's → atmosphere. Extremely tenuous, it lies above the → ionosphere from a height of about 500 km, to the edge of → interplanetary space.
2) An extremely tenuous kind of atmosphere surrounding a → solar system body. Since the → mean free path is much greater than the atmospheric scale height. The → atoms or → molecules never collide with each other. → lunar exosphere.

→ exo- + → sphere.

1) The act of expending something, especially funds; disbursement; consumption.
2) Something that is expended; expense (Dictionary.com).

From → expend.

Mid.Pers. uzên, uzênag "expense;" ultimately from Proto-Ir. *uz-ayana- literally "going out" (cf. Awromani ziāy-/-zia- "to go out"), from uz-, → ex-, + *Hai- "to go," → efficiency.

1) To travel to or in a place for the purpose of discovery.
2) To make a careful investigation or study of something.

From L. explorare "investigate, search out;" said to be originally a hunters' term meaning "set up a loud cry," from → ex- "out" + plorare "to cry."

Puyidan, originally "to run, trot; wander," from Mid.Pers. pôy-, pwd- "to run;" cf. Gk. speudein "to hasten;" Lith. spudinti.

A person or thing that explores.

Agent noun of → explore.

1) The act of exposing; the fact or state of being exposed, → expose.
2) In optics, the total radiant energy incident on a surface per unit area. It is equal to the integral over time of the radiant flux density.

Verbal noun of → expose.

In photography, an instrument used to measure the intensity of light from a scene to be photographed and to indicate the camera lens and shutter settings required to expose the film correctly.

→ exposure; → meter.

The length of time during which the receiver is irradiated.

→ exposure; → time.

1) To transform ideas into words; utter or state.
2) Math: To → transform into equivalent → terms. For example by → expanding or → factorizing an → expression. See also → suppress, → impress.

M.E. expressen, O.Fr. espresser "to press, squeeze out; speak one's mind," M.L. expressare, frequentative of exprimere "represent, describe," literally "to press out," from → ex- "out" + pressare "to press, push," from L. premere "to press, hold fast, cover, compress."

Zohâvidan, from zo- variant of os- "out," → ex-, + hâv, from Av. hau- "to press, squeeze out;" cf. Mid.Pers. hunîdan "to express, extract (juice)," hâwan "mortar;" akin to Skt. sav- "to press, press out;" O.H.G. sou, O.E. sēaw "juice;" + -idan infinitive suffix.

1) The act or an instance of expressing.
2) Math.: A statement using mathematical quantities such as → scalars, → variables, → parameters, → functions, and → sets, as well as → relational and → logical  → operators such as → equality, → conjunction, → existence, → union, etc. (Steven. G. Krantz, ed., Dictionary of Algebra, Arithmetic, and Trigonometry, 2001).

→ express; → -tion.

In → photometric calibration, the correction for energy loss undergone by radiation due to the → atmospheric extinction. Extinction correction is done using → standard stars observed at different → airmasses.

→ extinction; → correction.

1) (adj.) Of or from outside the limits of the Earth.
2) (n.) A hypothetical extraterrestrial being; → alien.

→ extra- + → terrestrial.

Life that may exist and originate outside the planet Earth.

→ extraterrestrial; → life.

Farthest from the center or middle; outermost; exceeding the bounds of moderation. → extreme adaptive optics; → extreme HB star; → extreme horizontal branch star; → extreme infrared; → extreme mass ratio inspiral; → extreme ultraviolet; → extremely metal-poor star.

From L. extremus "outermost, utmost," superlative of exterus, "outer," comparative of ex "out of," → ex-.

Ostom "outermost, utmost" (Av. (ustəma- "outermost, highest, ultimate"), superlative of ost "out," → ex-, + -tom superlative suffix, from Mid.Pers. -tom (xwaštom "most pleasant," nevaktom "best," wattom "worst"), from O.Pers. -tama- (fratama- "first, front"); Av. -təma- (amavastəma- "strongest," hubaiδitəma- "most sweet-scented," baēšazyôtəma- "most healing," fratəma- "first, front"); cf. Skt. tama-.

An → adaptive optics system with high-contrast imaging and spectroscopic capabilities. Extreme adaptive optics systems enable the detection of faint objects (e.g., → exoplanets) close to bright sources that would otherwise overwhelm them. This is accomplished both by increasing the peak intensity of point-source images and by removing light scattered by the atmosphere and the telescope optics into the → seeing disk.

→ extreme; → adaptive; → optics.

Same as → extreme horizontal branch star.

→ extreme horizontal branch star.

The hottest variety of stars on the → horizontal branch with temperatures ranging from 20,000 to 40,000 K. EHB stars are distinguished from normal horizontal branch stars by having extremely thin, inert hydrogen envelopes surrounding the helium-burning core. They are hot, dense stars with masses in a narrow range near 0.5 Msun. These stars have undergone such extreme mass loss during their first ascent up the giant branch that only a very thin hydrogen envelope survives. Stars identified as EHB stars are found in low metallicity globular clusters as an extension of the normal HB.

→ extreme; → horizontal; → branch; → star.

A portion of the far infrared radiation, including wavelengths between 100 and 1,000 microns.

→ extreme; → infrared.

A compact stellar remnant (e.g., a → white dwarf, → neutron star, or → black hole) that undergoes → inspiral into a much more massive object (→ supermassive black hole found → galactic centers). EMRIs are potential sources of low-frequency → gravitational waves. Predictions of the EMRI event rates span a wide range, from ~ 10^-9 to 10^-6 yr^-1 per galaxy (Merritt et al. 2011, Physical Review D 84, 044024). See also → resonant relaxation.

→ extreme; → mass; → ratio; → inspiral.