An Etymological Dictionary of Astronomy and Astrophysics

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.

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

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

Etymology (EN): 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).

Etymology (PE): 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”).

A prefix in the SI system of units denoting 10¹⁸.

See also: Adopted in 1991, from Gk. ex “six,” because it is equal to (1000)⁶.

1. Strictly accurate or correct; precise, as opposed to approximate.
   

2. The complete solution of an equation. For example, in the equation x² = 7, the positive solution 2.646 is correct to three decimal places. The exact answer is x = 7^1/2.
   

See also:
→ exact differential, → exact differential equation, → exact science, → accurate,
→ precise, → rigorous.

Etymology (EN): From L. exactus, p.p. of exigere, literally “to drive out, thrust out,” also “demand, finish, measure,” from → ex- “out”

• agere “drive, lead, act,” → act.

Etymology (PE): Razin “firm, solid, strong” [Dehxodâ, Steingass], Mid.Pers. razên “firm, strong, secure, solid.”

If N(x,y) is a → function of two → independent variables, then dN = (∂N/∂x)dx + (∂N/∂y)dy is the exact differential.

See also: → exact; → differential.

A → differential equation composed of → continuous  → differentiable functions for which certain conditions are fulfilled. The equation M(x,y)dx + N(x,y)dy = 0 is called exact if M(x,y) and N(x,y) are continuous differentiable functions for which the following relationship is fulfilled: ∂M/∂y = ∂N/∂x, and ∂M/∂y and ∂N/∂x are continuous in some region.

See also: → exact; → differential; → equation.

A value that is known with complete certainty. Examples of exact numbers are defined numbers, results of counts, certain unit conversions. Some examples: there are exactly 100 centimeters in 1 meter, a full circle is exactly 360°, and the number of students in a class can exactly be 25.

See also: → exact; → number.

A field of study that admits especially precise predictions and rigorous methods of testing hypotheses, especially reproducible experiments involving quantifiable predictions and measurements.

See also: → exact; → science.

1. The act of examining; inspection; inquiry; investigation.
   

2. The state of being examined.
   

3. The act or process of testing pupils, candidates, etc., as by questions (Dictionary.com).

See also: Noun from → examine.

1. To inspect or scrutinize carefully.
   

2. To inquire into or investigate.
   

3. To test the knowledge, reactions, or qualifications of (a pupil, candidate, etc.), as by questions or assigning tasks (Dictionary.com).

Etymology (EN): M.E., from M.Fr. examiner “interrogate, question,” from L. examinare “to test or try; consider,” literally “to weigh,” from examen “a means of weighing or testing,” probably ultimately from exigere “weigh accurately,” → exact.

Etymology (PE): Barrasidan, from bar- “up; upon; on; in; into; at; forth; with; near; before; according to,” → on-, + rasidan “to attain; to arrive,” → access.

One of a number of things, or a part of something, taken to show the character of the whole.

Etymology (EN): From O.Fr. essample, from L. exemplum “a sample,” literally “that which is taken out,” from eximere “to take out, remove,” from → ex-

• emere “to obtain, buy,” originally “to take,” from PIE base *em- “to take” (cf. Av. yam-, yās- “to hold, take hold of,” apayeiti (with apa) “taking away a thing from;” O.Pers. āyasa- “to take as one’s own;” Skt. yam- “to hold, sustain,” yamati “holds, subdues;” O.C.S. imo “to take;” Lith. imti, ima, émé “to take”).

Etymology (PE): Nemuné, from nemun “index; guide,” from nemudan “to show, display,” from Mid.Pers. nimūdan, from ne- “down; into;” O.Pers./Av. ni- “down; below; into,” → ni-, + mun, Av. māy- “to measure,” → display.

Possessing outstanding quality or superior merit; remarkably good (Dictionary.com).

Etymology (EN): M.E., from O.Fr. excellent “outstanding,” from L. excellentem (nominative excellens) “towering, prominent, superior,” pr.p. of excellere “to surpass, be superior,“from → ex- “out from” + cellere “to rise high, tower,” related to celsus “high, great,” from PIE root *kel- “to be elevated; hill;” from which are derived L. collis “hill,” columna “projecting object,” culmen “top, summit,” cellere “raise;” Gk. kolonos “hill,” kolophon “summit;” Lithuanian kalnas “mountain,” kalnelis “hill;” E. hill; Pers. dialects (Gilân) kol, kulâ “hill,” (Dâmqân) kalut, kolut “successive soil hills, hill,” (Tabari) keti “hill,” (Jâsk) kit “hill.”

Etymology (PE): Mid.Pers. pahrom “excellent,” variant pahlom, ultimately from *parθama- “the highest, the most elevated,” literally “Parthian,” adj. from Parθa(va)-; cf. pahlavân “hero,” another similar respect word related to Parthia (Nyberg 1974).

The center of an → excircle.

See also: → ex-; → center.

1. With the exclusion of; excluding.
   

2. To exclude; leave out.

Etymology (EN): From M.Fr. excepter , from L. exceptus, p.p. of excipere  “to take out,” from → ex- “out” + capere “to take,”
→ concept.

Etymology (PE): Sogert, from so-, variants zo- and os-, → ex- “out,” + gert- “to take,” → concept; cf. Mid.Pers. Parthian zgirw- “to take out,” from uz- “ex-” + girw- “to take.”

1. The act of excepting or the fact of being excepted.
   

2. Something excepted. 

See also: Verbal noun of → except.

Forming an exception; not ordinary.

See also: → exception; → -al.

The state or an instance of surpassing usual, proper, or specified limits. → color excess; → infrared excess.

Etymology (EN): From L. excessus “going beyond bounds,” from stem of excedere “to go beyond,” from → ex- “out” + cedere “to go, yield;” cf. Gk. hodos “way;” PIE base *ked- “to go, yield.”

Etymology (PE): Fozuni, from afzuni “excess,” afzuni kardan “to exceed bounds,” from afzudan “to add, increase,” from Mid.Pers. abzudan “to increase, grow;” O.Pers. abijav- “to increase, add to, promote,” from abi-, aiby- “in addition to; to; against” + root jav- “press forward;” Av. gav- “to hasten, drive;” Sk. jav- “to press forward, impel quickly, excite,” javate “hastens.”
Ferehbud “excess” (Mid.Pers. frehbūd “excess”),
from Mod.Pers. fereh, firih “much; more” + bud “to be.” The first component fereh, from Mid.Pers. frây “more, much,” from Av. frāyah- “more; too much, very much” (frāyô.humata- “rich in good thoughts”). The second component bud, budan “to be,” from
Mid.Pers. budan, from O.Pers./Av. bav- “to be; become, take place;” Av. buta- perf. ptcpl. pass., bavaiti “becomes”
(cf. Skt. bhavati “becomes, happens,” bhavah “becoming; condition, state;” PIE *bheu- “to be, come into being, become;”
Gk. phu- “become,” phuein “to bring forth, make grow;” L. fui “I was” (perf. tense of esse), futurus “that is to be, future;” Ger. present first and second person sing. bin, bist; E. to be; O.Ir. bi’u “I am;” Lith. bu’ti “to be;” Rus. byt’ “to be”).

1. To give and receive reciprocally.
   

2. The act, process, or an instance of exchanging. → exchange force, → exchange particle, → Prevost’s law of exchanges.

Etymology (EN): O.Fr. eschangier, from V.L. *excambiare, from L. → ex- “out” + cambire “barter.”

Etymology (PE): Mod.Pers. gahulidan “to exchange,” Kurd. guhartin/guhêr- “to exchange,” Mid.Pers. wihir “to change,” wihirišn “change,” Manichean Mid.Pers. hr’g; Buddhist Mid.Pers. hlg “duty, tribute; work, effort;” Arm. loanword hark “duty, tribute;” Ar. loanword xarj “expense,” xarâj “land, property tax;” Proto-Iranian *har- “to barter, trade; to pay tribute;” IE cognates: Gk. elein “to take (by force),” elor “loot, booty, catch;” Goth. saljan “to bring, to sacrifice;” O.E. sellan “to hand over, sell;” O.H.G. sala “delivery of goods.”

The force that governs the exchange of particles in the interaction between bodies. → exchange particle.

See also: → exchange, → force.

In quantum field theory, a particle that transfers momentum and energy between interacting objects, and is said to mediate the interaction. All four of the fundamental forces involve the exchange of one or more particles. For example, photon is the exchange particle of the electromagnetic force.

See also: → exchange, → particle.

Chemistry: A complex formed from combination of a molecule with another molecule of the same type but in an → excited state. In other words, a → dimer in an electronically excited state. See also → exciplex.

See also: From exci-, from → excited, + -mer, from → dimer.

Chemistry: A complex formed by association of a molecule in an → excited state and another molecule of a different type.
See also → excimer.

See also: From exci-, from → excited, + -plex, from → complex.

For a → triangle with two sides extended in the direction opposite their common → vertex,
a circle that lies outside the triangle and is tangent to the three sides (two of them extended). The center of the excircle, called the → excenter, is the point of intersection of the bisector of the interior angle and the bisector of the exterior angles at the other two vertices.

See also: → ex-; → circle.

To cut out or off; to remove

Etymology (EN): M.E., from M.Fr. exciser, from L. excisus, p.p. of excidere “cut out, cut down, cut off,” from → ex- + caedere “to cut,” → precise.

Etymology (PE): Osunidan, from os-, → ex- + sun “cut,” → precise.

The act of removal; an excising. The surgical removal of a foreign body or of tissue.

See also: Verbal noun of → excise.

1. The addition of → energy to an → atomic or → molecular system, → transferring it from its → ground state to an → excited state.
   

2. A property of an → emission nebula usually expressed by the ratio [O III] 5007Å/Hβ.

See also: Verbal noun of → excite; → -tion.

Amount of energy (usually measured in → electron-volts) required to bring an electron from its → ground state to a given → excited state.

See also: → excitation; → energy.

In quantum mechanics, the energy that is necessary to change a system from a → ground state to a given
→ excited state; also called excitation energy.

See also: → excitation; → potential.

Of a gas or plasma, the temperature deduced from the → populations of atomic → excited states, as expressed by the Boltzmann formula: N_u/N_l = (g_u/g_l) exp (-ΔE/kT_ex), where N_u and N_l are the upper level and lower level populations respectively, g_u and g_l the statistical weights,
ΔE = hν the energy difference between the states,
k is → Boltzmann’s constant, and h→ Planck’s constant. The higher the energy of the occupied states, the higher the excitation temperature.

See also: → excitation; → temperature.

Verb of → excitation.

Etymology (EN): From L. excitare “to rouse, produce,” freq. of exciere “to call forth, instigate,” from → ex- “out” + ciere “to move, set in motion;” PIE base *kei- “to move to and fro” (cf. Av. šiyav-, š(ii)auu- “to move, go,” šiyavati “goes,” šyaoθna- “activity; action; doing, working;” O.Pers. šiyav- “to go forth, set,” ašiyavam “I set forth;” Mod.Pers. šodan, šow- “to go; to become;” cf. Skt. cyu- “to move to and fro, shake about; to stir,” cyávate “stirs himself, goes;” Gk. seuo “I start quickly after,” kinein “to move;” Goth. haitan “call, be called;” O.E. hatan “command, call”).

Etymology (PE): Barangixtan, from intensive prefix bar- “on, upon, up,” → on-,

• angixtan, angizidan “to excite, stimulate,” from Mid.Pers. hangêxtan, hangêz- “to arouse, stimulate, stir up,” from Proto-Iranian *hamgaiz-, from ham-, → com-,
• *gaiz- “to disturb, stir, excite.” The Mod.Pers. gij, giž “confused, astonished, dizzy” is from this stem (Cheung 2007).

An atom in which one or more of its bound electrons are at → energy levels higher than their normal level.

See also: Excited p.p. of → excite;
→ atom.

The condition of a particle or system of particles (especially an atom, nucleus, molecule)
after absorbing energy from outside and transiting to a higher → energy level than that of its → ground state. Excited states are transitory as they lose energy through emissions or collisions and return to ground state.

See also: Excited, p.p. of → excite; → state.

A star associated with an interstellar ionized nebula (→ H II region or → planetary nebula) whose energetic → ultraviolet, → photons
→ ionize the nebula.

See also: Exciting, verbal adj. of → excite;
→ star.

To shut or keep out; to hinder from being included, considered, or accepted. → exclusion.

Etymology (EN): From L. excludere “to keep out, shut out, hinder,” from → ex- “out” + claudere “to close, shut,” → include.

Etymology (PE): Sokolândan, from so-, variant os-, → ex-, + kolândan “to shut,” → include.

An act or instance of excluding; the state of being excluded.

See also: Verbal noun of → exclude.

In → quantum mechanics, the principle according to which no → two → fermions of the same kind may simultaneously → occupy the same → quantum state. Also known as → Pauli exclusion principle.

See also: → exclusion; → principle.

Excluding or having power to exclude; excluding all else; rejecting other considerations, possibilities, etc.

See also: Adj. from → exclude.

A process in which an astronomical body loses mass mainly in the direction of its → equatorial regions, as opposed to → accretion.

See also: From L. → ex- + crescere “to grow,” → accretion.

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.

See also: → excretion; → disk.

1. A short trip or outing to some place, usually for a special purpose and with the intention of a prompt return.
   

   2. Physics: The displacement of a body or a point from a mean position or neutral value, as in an oscillation (Dictionary.com). → geomagnetic excursion.

Etymology (EN): From L. excursion- “a running forth, expedition,” figuratively “an outset, opening,” from excurrere “to run out,” from → ex- “out” + currere “to run,” → current.

Etymology (PE): Zocâr, literally “wander out, " from zo- “out,” → ex-, + câr “to come and go, wander,” related to car-, caridan “to psature, graze;” (Karingân) cârumé “excursion, walking around,” (Sorxé) câqâle, (Sangesar, Semnân) ceqala “excursion;” Av. car- “to come and go, wander;” cf. Skt. car- “to move, walk, go;” Gk. pelomai “I move;” L. colere “to till, cultivate;” PIE root *k^welH- “to move, turn, wander.”

1. Computers: Describing a computer program that is able to be run. → executable program.
   

2. Computer: A file containing a program that will run when it is opened. → executable file.

See also: → execute; → -able.

A type of binary file designed to be directly executed by a computer system. → executable program.

See also: → executable; → file.

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

See also: → executable; → program.

1. To carry out; accomplish.
   

2. To create (a work of art, for example) or carry out in accordance with a prescribed design.
   

3. Computers: To run a program or an instruction.

Etymology (EN): M.E. executen, from O.Fr. executer, from M.L. executare, from L. execut-/exsecut-, p.p. stem of exequi/exsequi “to follow out, carry out,” from → ex- “out” + sequi “to follow, come after,” from PIE root *sekw- “to follow,” → sequence; cf. Av. hac- “to follow,” Gk. hepesthai “to follow,” Skt. sacate “accompanies, follows”

Etymology (PE): Zokârdan, from prefix zo-, variants os-, so-, âz-, → ex-, + kâr variant of kar-, kardan “to do, to make,” → -ize.

The act of executing something; the state of being executed.

See also: Verbal noun of → execute; → -tion.

1a) Of, pertaining to, or suited for carrying out plans, duties, etc.

1b) Pertaining to or charged with the execution of laws and policies or the administration of public affairs.

2a) A person or group of persons having administrative or supervisory authority in an organization.

2b) The person or persons in whom the supreme executive power of a government is vested (Dictionary.com).

See also: → execute; → -ive.

A person who executes, carries out, or performs some duty, job, assignment, artistic work, etc. (Dictionary.com).

See also: → execute; → -or.

A period of three → Saros cycles, that is 54 years and 34 days (19,755.96 days) that can be used to predict successive → eclipses with similar properties and location.

As the Saros cycle

is a period of about 6.585 ¹/₃ days, the ¹/₃ day means that after 223 → lunar months all eclipses are shifted by about 8 hours (or by about 120° in longitude).

Exeligmos contains a whole number of → synodic months (669), it also contains a whole number of → anomalistic months (717), and → draconistic months (726). So, after one exeligmos, the Moon will again be near the same node of its orbit. Thus we have a very good chance of finding an eclipse.

Moreover, since an exeligmos also contains a whole number of days, the eclipse will even occur at about the same time of day as before. But because the Moon moves 32° in mean longitude, over and above complete cycles, during an exeligmos, the second eclipse will occur approximately one zodiac sign farther east than did the first one (James Evans & J. Lennart Berggren, Geminos’s Introduction to the Phenomena, A Translation and Study of Hellenistic Survey of Astronomy, 2006, Princeton Univ. Press).

Etymology (EN): Exeligmos, Gk. “turn of the wheel.”

Etymology (PE): Carxgard “turn of the wheel,” from carx, → wheel, + gard “turn,” → revolve.

1a) Something done or performed as a means of practice or training.

1b) A putting into action, use, operation, or effect. <BR>

2a) To put (faculties, rights, etc.) into action, practice, or use. <BR>

2b) To put through exercises, or forms of practice or exertion, designed to train,
develop, condition, or the like (Dictionary.com).

Etymology (EN): M.E., from M.Fr. exercice, from L. exercitium “training, exercise” (of soldiers, horsemen, etc.); from → ex- “off” + arcere “keep away, prevent, enclose.”

Etymology (PE): Âvaržeš, verbal noun from Âvaržidan, from prefix â- + varž, “work,” variant of varz, → practice, + infinitive suffix -idan.

To apply or put forth, as strength.

Etymology (EN): From L. ex(s)ertus, p.p. of exserere “to thrust out, put forth,” from → ex- “out,” + serere “to bind together.”

Etymology (PE): Balizidan, from Kurd (Kurm.) bil “work,” bilîn “to work,” variant of varz, → practice, + infinitive suffix -idan.

1. Vigorous action; physical or mental effort.
   

   2. The application or exercise of force, power, or faculties.

See also: → exert; → -tion.

1. To drain of strength or energy, wear out, or fatigue greatly, as a person.
   

   2. To use up or consume completely; expend the whole of.
      

   3. To empty by drawing out the contents; to create a vacuum in.
      

   4. To draw out all that is essential in (a subject, topic, etc.); treat or study thoroughly (Dictionary.com).

Etymology (EN): L. exhaustus, p.p. of exhaurire “to draw off, take away, use up, empty,” from → ex- “off” + haurire “to draw up” (as water), from PIE *heusio- “to scoop.”

Etymology (PE): Halanjidan, from Sorâni Kurd. halenjidan “to draw water,” variants hanjidan, âxtan, âhixtan, âhiz-, hanjidan, lenj- “to draw, to pull” Mid.Pers. âhynj- “to draw up,” other Pers. cognate sanjidan, farhang, nehang, etc.; ultimately from prefixed (*a-) Proto-Ir. *θanj- “to pull, draw;” Av. θanj- “to pull, to draw.”

1. Completely used up.
   

   2. Very tired.

See also: Past participle of → exhaust.

1. The act or process of exhausting.
   

   2. The state of being exhausted.
      

   3. Extreme weakness or fatigue.
      

   4. The total consumption of something (Dictionary.com).

See also: → exhaust; → -tion.

1. Comprehensive in scope; thorough.
   

   2. Tending to exhaust or drain, as resources or strength (Dictionary.com).

Etymology (EN): → exhaust; → -ive.

Etymology (PE): Ospor, → perfect; halanj, halanji, → exhaust.

1. To have actual being or reality; to be.
   

2. To have life; to live.

Etymology (EN): M.E., from O.Fr. exister, ultimately from pr.p. of L. existere/exsistere “to stand forth, appear; to exist, be;” from → ex- + sistere “cause to stand,” from PIE *sta-, cf. Pers. istâdan “to stand,”
→ state.

Etymology (PE): Hastumand budan, from Mid.Pers. hastumand “existing, existent,” from hast, ast ‘is" (infinitive hastan, astan);
O.Pers. astiy; Av. asti “is;” O.Pers./Av. root ah- “to be;” cf. Skt. as-; Gk. esti; L. est; PIE *es-, + euphonic -u-, + -mand possession suffix, → -ist, + budan “to be,” to become;" Mid.Pers. butan “to be ,become,” from O.Pers./Av. bav- “to be; become, take place,” Av. buta- perf. ptcpl. pass., bavaiti “becomes,”
Skt. bhavati “becomes, happens,” bhavah “becoming; condition, state,” PIE *bheu- “to be, come into being, become;” cf. Gk. phu- “become,” phuein “to bring forth, make grow,” L. fui “I was” (perf. tense of esse), futurus “that is to be, future,” Ger. present first and second person sing. bin, bist, E. to be, O.Ir. bi’u “I am,” Lith. bu’ti “to be,” Rus. byt’ “to be.”

Math.: The fact that at least one → solution exists for a given → problem.

See also: → exist; → -ence.

Math: The question of whether a → solution to a given → problem exists.

See also: → existence; → problem.

Math.: An → argument that establishes an → existence theorem.

See also: → existence; → proof.

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

See also: → existence; → theorem.

Existing; having existence.

See also: → exist.

1. Of or relating to → existence, especially  human existence.
   

2. Philo.:  Pertaining to what exists, and is thus known by experience rather  than reason; empirical as opposed to theoretical.
   

3. Logic: Denoting or relating to a → formula or → proposition asserting the
   existence of at least one object fulfilling a given condition; containing an → existential quantifier.
   

4. Of or relating to → existentialism (Dictionary.com).

Etymology (EN): From L.L. existentialis, → existence, → -al.

Etymology (PE): Hastiyâl, from hasti, → existence, + -al a suffix of attributes forming adjectives that often become nouns, in this case preferred to -i because hasti ends in -i, → -al.

A symbol of → predicate logic which expresses that the statements within its scope are → true for at least one instance of something. The symbol ∃ is used as the existential quantifier. Existential quantifiers are normally used in logic in → conjunction with → predicate symbols, which say something about a → variable or → constant, in this case the variable being quantified (→ quantify, → quantification).

See also: → existential; → quantifier.

A philosophical attitude associated especially with Heidegger, Jaspers, Marcel, and  Sartre, and opposed to → rationalism and  → empiricism, that stresses the individual’s  unique position as a self-determining agent responsible for the authenticity of his or  her choices (Dictionary.com).

See also: → existential; → -ism.

An advocate of → existentialism.

See also: → existential; → -ist.

A way or passage out.

Etymology (EN): From L. exit “he or she goes out,” from exire “to go out,” from → ex- “out” + ire “to go;” cf.
Gk ion " going," neut. pr.p. of ienai “to go;” Pers. ây-, â- present stem of âmadan “to come;” O.Pers. aitiy “goes;” Av. ay- “to go, to come,” aēiti “goes;” Skt. e- “to come near,” eti “arrival;” Goth. iddja “went,” Lith. eiti “to go;” Russ. idti “to go.”

Etymology (PE): Osraft, from os-, → ex- “out,” + raft, raftan “to go, walk,” → entrance.

In an → optical system, the → image of the → aperture stop formed by the elements following it. See also → entrance pupil.

See also: → exit; → pupil.

Prefix meaning “outside; outer; external” used in the formation of compound words: exoplanet, exosphere, exocentric.

Etymology (EN): From Gk. exo “outside,” used in forming scientific terms, → ex-.

Etymology (PE): Borun-, from borun “out, the outside” (Mid.Pers. bêron, from bê “outside, out, away”

• rôn “side, direction;” Av. ravan- “(course of a) river”).

The altitude at which the atmosphere becomes collisionless.

See also: → exo-; → base.

The study of life beyond the Earth’s atmosphere, as on other planets; also → astrobiology.

See also: → exo-; → biology.

An → exoplanet similar to Earth.

See also: → exo- + → earth.

→ extraterrestrial life.

See also: → exo-; → life.

A → European Space Agency (ESA) program to investigate the Martian environment and to demonstrate new technologies paving the way for a future Mars sample return mission in the 2020’s.

Two missions are foreseen: one consisting of an Orbiter plus an Entry, Descent and Landing Demonstrator Module (EDM), launched in 2016, and the other, featuring a rover, with a launch date of 2018. Both missions will be carried out in cooperation with Russia’s Roscosmos space agency.

The ExoMars program will demonstrate a number of essential flight and in-situ enabling technologies that are necessary for future exploration missions, such as an international Mars Sample Return mission.

At the same time, a number of important scientific investigations will be carried out.

The 2016 mission included a Trace Gas Orbiter (TGO) and an EDM. The Orbiter will carry scientific instruments to detect and study atmospheric trace gases, such as methane. The EDM will contain sensors to evaluate the lander’s performance as it descends, and additional sensors to study the environment at the landing site.

The 2018 mission includes a rover that will carry a drill and a suite of instruments dedicated to exobiology and geochemistry research.

See also: ExoMars, short for “→ exobiology on → Mars.”

A natural → satellite orbiting an → extrasolar planet.

See also: → exo-; → moon.

Same as → extrasolar planet.

See also: → exo- + → planet.

Of, relating to, or resembling an → exoplanet or exoplanets.

See also: → exoplanet; → -ary.

A → planetary system consisting of → exoplanets orbiting a star other than Sun.

See also: → exoplanetary; → system.

The passage of an → exoplanet across the face its star.

See also: → exoplanetary; → transit.

The part of → astrophysics that searches and studies → extrasolar planets.

See also: → exoplanet; → -logy.

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.

See also: → exo- + → sphere.

Relating to or describing any process in which a system releases heat to its surrounding environment.

Etymology (EN): From → exo- + -therm, from Gk. therme “heat,” from PIE *ghwerm-/*ghworm- “warm;” cf. Pers. garm “warm;” L. fornax “an oven;” O.E. wearm “warm” + → -ic.

Etymology (PE): From garmâ “heat, warmth” (Mid.Pers. garm; O.Pers./Av. garəma- “hot, warm;” cf. Skt. gharmah “heat;” Gk. thermos “warm;” L. formus “warm;” P.Gmc. *warmaz; O.E. wearm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm-, as above) + zâ verbal adj. and agent noun of zâdan “to bring foth, give birth,” (Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazâite, zâta- “born;” cf. Skt. janati “begets, bears;” L. gignere “to beget;” PIE base *gen- “to give birth, beget”).

1. Of foreign origin or character; not native; introduced from abroad, but not fully naturalized or acclimatized.
   

2. Strikingly unusual or strange in effect or appearance.
   

3. Of a uniquely new or experimental nature (Dictionary.com).
   

See: → exotic star.

Etymology (EN): M.E., from M.Fr. exotique and directly from L. exoticus, from Gk. exotikos “foreign,” literally “from the outside,” from → exo- “outside.”

Etymology (PE): Osgânik, from os-, → ex-, + gân relation suffix, from Mid.Pers. -gânag, -gâna, + -ik, → -ic.

A hypothetical → compact object composed of particles other than electrons, protons, and neutrons balanced against → gravitational collapse by → degeneracy pressure of corresponding quantum properties.

See also: → exotic; → star.

1a) To change (something) from a smaller form and/or size to a larger one.

1b) To increase the extent, number, volume or scope of (something).

1c) To express (something) at length and/or in detail.

1d) Math.: To write (a mathematical expression) as a sum of terms in an extended form.

2. to increase or grow in extent, bulk, scope; to spread out; unfold; develop.
   

See also → spread, → extend, → dilate.

Etymology (EN): M.E. expanden, from O.Fr. espandre “to spread, spread out,” from L. expandere “to spread out, unfold, expand,” from → ex- “out” + pandere “to spread, stretch,” from nasalized form of PIE root *pete- “to spread,” a Pers. offshoot of which is pahn “wide, broad,” as below.
from

Etymology (PE): Sopândan, “to stretch, to extend, open out” from so- “out,” → ex-, + pân, from pan, variant of pahn “wide, large, broad, ample, extensive,” from Mid.Pers. pah(a)n; Av. paθana- “broad, wide, spacious;” PIE root *pete- “to spread;” cf. L. patere “to be open,”
Gk. petannynai “to spread out,” petalon “a leaf.”

Alternatively, sopândan “to open up, to open out,” from so- “out,” → ex-, + pân “open,” cf. Yaghnobi pen, peyn “to open, unroll,” Sogd. pyn- “to open,” ultimately from Proto-Ir. *apa- “off, away, from” + *hHai- “to chain, bind,” from which Pers. gošâdan “to open, release” (Cheung 2007).

A → radio interferometer array consisting of 27 25-meter diameter antennas located on the Plains of San Agustin in West-Central New Mexico.
EVLA will operate at any frequency between 1.0 and 50 GHz and will have a continuum sensitivity improvement over the → VLA by factors of 5 to 20.The EVLA project is expected to be completed in 2012. See also the EVLA homepage.

See also: → expand; → very; → large; → array.

The deduction based on the observational fact that the greater the → distance to a → galaxy, the greater the → redshift in its → spectral lines (→ Doppler effect). The observations strongly indicate that galaxies appear to be moving away from us with speeds proportional to their distance. This is in agreement with the overall → expansion of the → Universe.

See also: → expand; → -ing; → Universe.

1. General: The act or process of expanding; the state or quality of being expanded. → expansion of the Universe.
   

2. Math.: The process of expressing a quantity, or a quantity expressed,
   as a sum of a series of terms. For example the expression (2x - 1)(x + 3) can be expanded to: 2x² + 5x - 3. See also → binomial expansion.

See also: Noun from → expand.

The receding of galaxies from one another at a speed proportional to their separation, as inferred by Edwin Hubble from the observed Doppler shift of distant galaxies. → Hubble constant describes the local rate of the expansion.

See also: → expansion; → universe.

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.

See also: → expansion; → parameter.

Statistics: Same as → mathematical expectation, → expected value.

Etymology (EN): From L. expectare “to await, hope,” from → ex- “thoroughly” + spectare “to look,” from → specere “to look at,” → -scope.

Etymology (PE): Bayusesš, verbal noun of bayusidan “to expect;” Mid.Pers. pyws- “to hope for, desire” (prefixed *pati-); O.Pers. vasiy “at will, greatly, utterly,” vašna- “will, favor;” Av. vas- “to will, desire, wish, long for,” vasəmi “I wish,” vasna- “will, favor,” ušti- “desire, wish, will,” vasô, vasə “at one’s will.” This word is extant in several Mod.Pers. dialects, Tabari vessen “to wish, desire,” Gilaki vâssan “to wish, desire,” vâsti “desire,” Kurd. wistin “to desire, wish,” Lâri avessa “to desire,” colloquial Tehrâni vâsé “for” (Mid.Pers. vasnâd “because”);
cf. Skt. vaś- “to wish, want, desire,” váśa- “wish, desire,” vasēna “for, because;” Gk. ekon “voluntary;” PIE base *uek- “to wish.”

Statistics: Same as → mathematical expectation, → expectation.

See also: → expectation; → value.

To use up. See also → spend, → consume.

Etymology (EN): From L. expendere “to pay out, weigh out money,” from → ex- “out” + pendere “to pay, weigh.”

Etymology (PE): Hazinidan, back formation from haziné, → expenditure.

1. The act of expending something, especially funds; disbursement; consumption.
   

2. Something that is expended; expense (Dictionary.com).

Etymology (EN): From → expend.

Etymology (PE): 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.

An act or operation for the purpose of discovering something unknown or of testing a principle, supposition. See:

→ Aspect experiment, → Carnal-Mlynek experiment, → Davisson-Germer experiment, → double-slit experiment, → Eratosthenes experiment, → Hafele-Keating experiment, → Hertz experiment, → Michelson-Morley experiment, → Millikan’s oil-drop experiment, → Pascal’s barrel experiment, → random experiment, → Stern-Gerlach experiment, → thought experiment, → toothed-wheel experiment, → Trouton-Noble experiment, → Young’s experiment.

Etymology (EN): From O.Fr. experiment, from L. experimentum “a trial, test,” from experiri “to test, try,” from → ex- “out of” + peritus “experienced, tested.”

Etymology (PE): Âzmâyeš, verbal noun of âzmudan, âzmây- “to try, experiment, test;” Mid.Pers. uzmudan, ôzmutan “to test, try, prove;” from O.Pers./Av. *uz-māy-, from uz-, → ex- + mā(y)- “to measure,” Proto-Ir. *maH- “to measure;” PIE *meH- “to measure;” cf. Skt. mati “measures,” matra “measure;” Gk. metra “lot, portion;” L. metri “to measure.”

1. To make plain or clear; to render understandable or intelligible.
   

2. To make clear the cause or reason of; to account for.
   

3. To assign a meaning to; → interpret.

Etymology (EN): From L. explanare “to make level, smooth out; make clear,” from → ex- “out” + planus “flat; clear.”

Etymology (PE): Ostâhidan, literally “to unfold, spread out” (on the model of Fr. expliquer, Sp. explicar, from L. → ex- “out”

• plicare “to lay, fold, twist,” from PIE base *plek- “to plait, twist;” cf. Gk. plekein “to plait,” L. plectere “to plait, braid, intertwine,” O.C.S. plesti “to braid, plait, twist,” Goth. flahta “braid”), from os- “out,” → ex- + tâh “fold, plait, ply;”
  Mid.Pers. tâg “piece, part” + -idan infinitive suffix.

1. The act or process of explaining.
   

2. A statement made to clarify something and make it understandable.

See also: Verbal noun of → explain.

1. General: Precisely and clearly expressed.
   

2. Math.: → explicit function.

Etymology (EN): From Fr. explicite, from L. explicitus “unobstructed,” variant p.p. of explicare “unfold, unravel, explain,” → explain.

Etymology (PE): Ostâhi, from ostâh present stem of ostâhidan,
→ explain, + -i adj. suffix.

The most usual form of a function in which the dependent variable (written on the left hand side of the Same as → equality sign)
is expressed directly in terms of independent variables written on the left (on the right hand side). See also → implicit function.

See also: → explicit; → function.

Verbal form of → explosion.

Etymology (EN): From L. explodere “drive out or off by clapping,” originally theatrical, “to drive an actor off the stage by making noise,” from → ex- “out” + plaudere “to clap, beat,” of uncertain origin.

Etymology (PE): Oskaftidan, from os-, → ex- + kaftidan “to burst; to split,” variants kaftan, kâftan “to split; to dig,” Parthian Mid.Pers. q’f- “to split;” Sogdian kβ “to spli;” Chorasmian kf- “to split, be split;” Proto-Iranian *kap-, *kaf- “to split.”

1. An act or instance of exploring or investigating; examination.
   

2. The investigation of unknown regions.
   

3. The process of searching for minerals by means of geological studies.
   
4. Medicine: An examination or investigation for diagnostic purposes, usually involving endoscopy or a surgical procedure.

See also: Verbal noun of → explore.

1. To travel to or in a place for the purpose of discovery.
   

2. To make a careful investigation or study of something.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: Agent noun of → explore.

The sudden and violent release of mechanical, chemical, or nuclear energy from a confined space which creates a heat wave that travels at → subsonic speeds. → detonation; → deflagration; → implosion.

See also: Verbal noun of → explode.

1. (n.) A chemical or compound that causes a sudden, almost instantaneous release of pressure, gas, heat, and light when subjected to sudden shock, pressure, high temperature, or applied potential.
   

2. (adj.) Pertaining to or of the nature of an → explosion.

Etymology (EN): From explos(ion), → explosion + → -ive.

Etymology (PE): Oskaftâk, from oskaft-, stem of oskaftan,
→ explode, + -âk noun suffix.

The explosive processes that are believed to occur in supernovae. Explosive carbon burning occurs at a temperature of about 2 × 10⁹ degrees and produces the nuclei from neon to silicon. Explosive oxygen burning occurs near 4 × 10⁹ degrees and produces nuclei between silicon and calcium in atomic weight.At higher temperatures, still heavier nuclei are produced.

Etymology (EN): → explosive; → nucleosynthesis.

1. The state or quality of being explosive.
   

2. A measure of the extent to which a material is explosive.

See also: → explosive; → -ity.

Math.: A symbol or number placed above and after another symbol or number (called the base) to denote the power to which the latter is to be raised. Examples: n in the expresseion aⁿ; 3 in the expression 2³.

Etymology (EN): From L. exponentem, pr.p. of exponere “put forth, explain,” from → ex- “forth” + ponere “to put, to place.”

Etymology (PE): Nemâ, agent noun of nemudan “to show, display,” from Mid.Pers. nimūdan, from ne- “down; into;” O.Pers./Av. ni- “down; into,” → ni-, + mun, Av. māy- “to measure,” → display.

Of or expressed by a mathematical → exponent. → exponential curve, → exponential equation, → exponential function.

See also: → exponent + -ial, variant of → -al.

A curve that represents an → exponential function.

See also: → exponential; → curve.

An equation in which unknowns appear as exponents. Examples: 2^{3x + 1} = 32.

See also: → exponential; → equation.

A function in the form of y = b^x defined for every → real number x, with positive base b > 1.

See also: → exponential; → function.

In an exponential manner.

See also: → exponential; → -ly.

1a) To ship (commodities) to other countries or places for sale, exchange, etc.

1b) Computers: To save (documents, data, etc.) in a → format usable by another → software program.

2. The act of exporting (Dictionary.com).

Etymology (EN): From L. exportare “to carry out, bring out; send away,,” from → ex- “away” + portare “carry.”

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

• bart variant of bord, bordan “to carry” (such as in dialects of Varzaneh barte, Nâin barte, Xonsâr birt, Esfahân bärten);
  Mid.Pers. burdan;
  O.Pers./Av. bar- “to bear, carry,” barəθre “to bear;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry;” PIE base *bher- “to carry.”

1. To reveal, make known, make visible.
   

   2. In imaging, to subject, as to the action of light, or other electromagnetic radiations.

Etymology (EN): M.E. exposen, from O.Fr. exposer “lay open, set forth,” from L. exponere “set forth, lay open, exhibit,” with contamination from poser “to lay, place” (→ position). doublet of expound.

Etymology (PE): 1) Osnehâdan, from os-, → ex-,

• nehâdan “to put, place,” → position.
  

2. nur dâdan, from nur, → light

• dâdan “to give,” 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;”
  PIE base *do- “to give.”

A formal exposition of facts.

Etymology (EN): From Fr. exposé, p.p. of exposer, “to → expose.”

Etymology (PE): Noun from osnehâdan, → expose.

1. The act of setting forth information or a viewpoint.
   

   2. Public exhibition or show.

See also: Verbal noun of → expose.

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.

See also: 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.

See also: → exposure; → meter.

The length of time during which the receiver is irradiated.

See also: → 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.

Etymology (EN): 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.”

Etymology (PE): 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).

See also: → express; → -tion.

To stretch out; draw out to the full length; to enlarge the scope of; to increase the length or duration of.

Etymology (EN): From O.Fr. estendre, from L. extendere “stretch out,” from → ex- “out” + tendere “to stretch,” see below.

Etymology (PE): Ostanidan, from os-, → ex- + tanidan as in Av. ustāna- “stretched out” (ustāna-zasta- “with outstretched hands”), cf. Skt. uttāná- “stretched out, spread out.” Mod.Pers. tanidan “to spin, twist, weave;” Mid.Pers. tanitan, from
Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend," tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch.”

An object whose angular size exceeds the resolution of the instrument used to observe it.

See also: → extended; → object.

In radio astronomy, a source whose angular extent could be measured, as distinguished from a point source.

See also: → extended; → source.

1. An act or instance of extending; the state of being extended.
   

2. Physics: That property of a body by which it occupies space.
   

3. Math.: A field F is said to be an extension of a field K if K is a subfield of F.
   

4. Logic: The sum of all individuals or objects to which the comprehension of a term is applied. For example, the extension of the term “dog” is the set of all (past, present and future) dogs in the world.

See also: Verbal noun of → extend.

The range over which a thing extends; length, area, volume, or scope.

See also: → extension.

1. Outer; being on the outer side; situated or being outside, which is outside.
   

   2. Outside; an exterior part or surface.

Etymology (EN): From L. exterior “outward, outer, exterior,” comparative of exterus “on the outside, outward, outer, foreign,” itself a comparative of → ex- “out of.”

Etymology (PE): Boruni, from borun, variant of birun “out, the outside,” → out.

1. Any of the four angles that do not include a region of the space between two lines intersected by a third straight line (→ transversal).
   

   2. The angle between any side and an extension of an adjacent side of a polygon.

See also: → exterior; → angle.

Of or pertaining to the outside or outer part.

Etymology (EN): M.E., from M.Fr. externe or directly from L. externus “outside, outward,” from exterus, a comparative of → ex-,

• → -al.

Etymology (PE): Biruni, adj. from birun “out, the outside,” → out.

The → photoelectric effect in solids where free electrons are emitted from the surface of a substance (e.g., → semiconductor) when radiation of appropriate frequency falls on it. Also called → photoemissive effect.

See also: → external; → photoelectric; → effect.

The work done by a thermodynamic system as it expands against its surrounding environment. It is equal to ∫pdV, where p is the applied external pressure and V the volume, integrated from the initial V₁ to final V₂.

See also: → external; → work.

Verbal noun of → externalize.

See also: → externalize + → -tion.

1. To make external; embody in an outward form.
   

2. To regard or treat as being caused by externals; attribute to external causes (Dictionary.com).

See also: → external + → -ize.

1. Dimming of light by an intervening medium (the Earth’s atmosphere or the interstellar medium). It is usually due to both scattering and absorption.
   
2. Paleontology: The act or process of dying out or coming to an end, becoming extinct: the extinction of a species; → mass extinction.

Etymology (EN): Noun of extinct, from L. extinctus, p.p. of extinguere “to quench, wipe out,” from → ex- “out” + stinguere “to quench,” from PIE base *steig- “to prick, stick, pierce;” cf. Mod.Pers. tiz, tež, tig, tej, tij, tiq
“sharp;” Av. tiγra- “pointed,” tiγray- “arrow;” → deblur.

Etymology (PE): Xâmuši, noun of xâmuš “extinguished; silent,” Mid.Pers. xâmôš “silent;” cf. Skt. amrs- “to bear patiently.”

Gradient of apparent magnitude with air mass.

See also: → extinction; → coefficient.

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.

See also: → extinction; → correction.

A graph representing the variation of the → interstellar extinction against → wavelength. Usually it displays the → normalized values of extinction as a function of (the → inverse) of the wavelength (in → microns). See, e.g., Sandage & Mathis, 1979, Ann. Rev. Astron. Astrophys. 17, 73.

See also: → extinction; → curve.

Stars specifically observed at selected air masses in view of determining the atmospheric extinction coefficients.

See also: → extinction; → star.

A facility at → European Southern Observatory (ESO)’s → La Silla Observatory funded by the European Research Council and the French Agence National de la Recherche with the purpose of detecting and studying → transiting  → exoplanets. ExTrA will search for Earth-sized planets orbiting nearby → red dwarf stars.

It uses three 0.6-metre telescopes. They regularly monitor the amount of light received from many red dwarf stars and look for a slight dip in brightness that could be caused by a planet passing across a star’s disk and obscuring some of its light.

The three ExTra telescopes collect light from the target star and four comparison stars and that light is then fed through optical fibres into a → multi-object spectrograph. This innovative approach of adding → spectroscopic information to traditional photometry helps mitigate the disruptive effect of Earth’s atmosphere, as well as effects introduced by instruments and detectors, thus increasing the precision achievable.

See also: ExTrA, short for Exoplanets in Transits and their Atmospheres, → exoplanet; → transit; → atmosphere.

Prefix meaning “outside; beyond the scope of; in addition to what is used or expected.” Also extro-.

Etymology (EN): M.E., from L. extra, adverb and preposition, “outside, except, beyond,” from exter “outward, on the outside.”

Etymology (PE): Ostar-, from os-, → ex-, + -tar comparative suffix (Mid.Pers. -tar; Av. -tara; PIE base *-tero); borun-, from borun “out, the outside” (Mid.Pers. bêron, from bê “outside, out, away”

• rôn “side, direction;” Av. ravan- “(course of a) river”).

1a) To draw or pull out, often with great force or effort.

1b) To obtain from a substance by chemical or mechanical action, as by pressure, distillation, or evaporation.

1c) To derive or obtain (information, for example) from a source.

1d) Math.: To determine or calculate (the root of a number).

2. Something extracted (FreeDictionary.com).

Etymology (EN): From L. extractus, p.p. of extrahere “to draw out,” from → ex-“out, out of” + trahere “to draw” “to pull, draw,” from PIE root *tragh- “to draw, drag, move.”

Etymology (PE): Barhanjidan, from bar- “on; upon; against; before; at; in,” → object,

• hanjidan “to draw, to pull,” variants âxtan, âhixtan, âhiz-, halanjidan, lenjidan; Mid.Pers. âhynj- “to draw up,” other Pers. cognate sanjidan, farhang, nehang, etc.; ultimately from prefixed (*a-) Proto-Ir. *θanj- “to pull, draw;” Av. θanj- “to pull, to draw.”

1. The act of extracting or the condition of being extracted.
   

   2. Something obtained by extracting; an extract (FreeDictionary.com).

See also: → extract; → -tion.

Of, pertaining to, or dealing with the space beyond the Milky Way.

See also: From → extra- + → galactic.

The branch of astronomy that deals with objects beyond the Milky Way, especially galaxies and quasars.

See also: → extragalactic; → astronomy.

The integrated intensity of all of the light emitted throughout the history of the Universe across the whole of the → electromagnetic spectrum,
including those which are not individually detected. The EBL spectrum includes cosmological backgrounds associated with either primordial phenomena, such as the → cosmic microwave background radiation (CMBR),
or photons emitted by stars, galaxies and → active galactic nuclei (AGN) due to → nucleosynthesis or other → radiative processes, including → dust scattering, → absorption and reradiation. The EBL may also contain signals that are diffuse and extended, including high-energy photons associated with dark matter particle decays or annihilation.

See also: → extragalactic; → background; → light.

1. Beyond what is usual, ordinary, regular, or established.
   

2. Exceptional in character, amount, extent, degree, etc. (Dictionary.com). → unordinary.

See also: → extra-; → ordinary.

When a beam of → unpolarized light is incident on a → doubly refracting crystal, there will be two refracted rays. The ray for which → Snell’s law does not hold.

See also: → extraordinary; → ray.

Math.: To estimate the value of a result outside the range of a series of known values.

Etymology (EN): From → extra- + (inter)polate, → interpolate.

Etymology (PE): From borun, → extra- + 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.”

Predicting the value of unknown data points by projecting a function beyond the range of known data points.

See also: Verbal noun of → extrapolate.

Not belonging to the → solar system; outside, or originating outside, the solar system.

See also: → extra-; → solar.

A planet which belongs to a star other than → Sun, and therefore does not belong to our → solar system; same as → exoplanet.

See also: → extrasolar; → planet.

A → planatary system around a star other than the Sun. Same as → exoplanetary system .

See also: → extrasolar; → system.

1. (adj.) Of or from outside the limits of the Earth.
   

2. (n.) A hypothetical extraterrestrial being; → alien.

See also: → extra- + → terrestrial.

Life that may exist and originate outside the planet Earth.

See also: → 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.

Etymology (EN): From L. extremus “outermost, utmost,” superlative of exterus, “outer,” comparative of ex “out of,” → ex-.

Etymology (PE): 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.

See also: → extreme; → adaptive; → optics.

Same as → extreme horizontal branch star.

See also: → 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.

See also: → extreme; → horizontal; → branch; → star.

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

See also: → 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.

See also: → extreme; → mass; → ratio; → inspiral.

A part of the ultraviolet radiation with wavelengths between 50 and 300 Angstöms.

See also: → extreme; → ultraviolet.

A star with an iron abundance [Fe/H] < -3 found in a → galactic halo. These stars,
whose → metallicity is typically less than one thousandth
of the solar value, are believed to have formed shortly after the → Big Bang, 13.7 billion years ago. The number of such stars depends on the primordial → initial mass function. If the IMF were steep, there could, in principle, be a lot of EMPSs formed at high → redshifts. Thus many of them could have ended up in the halos of galaxies. See also → Population III star.

See also: → extreme; → metal; → poor; → star.

A → microorganism with the ability to thrive in extreme environmental conditions that would kill other species. These conditions include high temperatures, very low temperatures, high pressures, high levels of radiation, and high concentrations of salt in water.

See also: → extreme; → -phile.

A maximum or minimum value of a function in a specified interval.

Etymology (EN): From L. extremus, → extreme.

Etymology (PE): Ostomé, from ostom, → extreme

• noun suffix -é, from Mid.Pers. -ag.

Not essential or inherent; not forming part of or belonging to a thing. → intrinsic.

Etymology (EN): Extrinsic, from L.L. extrinsecus “outward,” from extrim- + secus “beside,” from sequi “to follow.”

Etymology (PE): Borungin, from borun “out, the outside” (Mid.Pers. bêron, from bê “outside, out, away”

• rôn “side, direction;” Av. ravan- “(course of a) river”) + -gin adj. suffix, contraction of âgin “filled.”

Photoconductivity due to the addition of impurities or external causes.

Etymology (EN): → extrinsic; → photoconductivity.

Etymology (PE): Šidhâzandegi, → photoconductivity; borungin, → extrinsic.

A semiconductor, such as silicon, whose responsive properties can be altered by the addition of impurities. Copper- and mercury-doped germanium are both examples of this semiconductor material.

See also: → extrinsic; → semiconductor.

A star whose variation in apparent brightness is not
due to changes in the star itself but to some external cause, such as eclipsing by a companion.

See also: → extrinsic; → variable; → star.