An Etymological Dictionary of Astronomy and Astrophysics

1. In an optical system, the point to which light rays are converged (real image) or from which they appear to diverge (virtual image) after reflection or refraction.
   Math.: A number, point, or unique element of a space that corresponds to some other number, point, or unit element.
   

2. To make an image of; to picture or represent in the mind.

Etymology (EN): From O.Fr. image, from L. imaginem (nom. imago) “copy, picture, likeness " from stem of imitari “to copy, imitate,” from im-, stem of imitare “to copy, imitate” + -ago noun suffix.

Etymology (PE): 1) Vine, from (Sorani) Kurd. vina or vena “image, picture; similar,” from vin/ven, variant of bin, present stem of dîtin, Pers. didan “to see, to look;” cf. Taleshi vinde “to see,” Tati vindiyan “to see,” Persian bin-, didan “→ see.” The relation between “image” and “see” is probably from the fact that the image of a subject can be seen without its presence.
Tasvir, loan from Ar.

2. Infinitive with gereftan “take,” → take, and dâštan “to have, to hold,” → property.

The process of adding several usually low-exposure images to create an image having a significantly higher signal/noise ratio.

See also: → image; → co-; → add.

A technique using a mathematical model of the blurring process to recover the original, sharp image. See also → blurred image.

See also: → image; → deburring.

The meeting of light rays emanating from an object after crossing an optical system.

See also: → image; → formation.

Device that produces an observable image that is brighter at output than the image at input.

See also: → image; → intensifier.

The plane in which is formed an image produced by an → optical system.

See also: → image; → plane.

One of the points constituting an extended image formed in an → optical system.

See also: → image; → point.

The use of techniques to produce, extract, identify, and display images for evaluation, interpretation, and further interaction with the data.

See also: → image; → processing.

1. The degree of visibility of relevant → information
   in an image.
   

2. The → full-width at half-maximum of a long exposure stellar image obtained by an instrument mounted on a telescope observing in the presence of → seeing.

See also: → image; → quality.

The separation between two detached but adjacent points in an image.

See also: → image; → resolution.

The process by virtue of which the original image can be created by removing the blurring and the noise that occur during image formation.

See also: → image; → restoration.

The quantity that relates the length on the image to the angular or physical separations on the sky.

See also: → image; → scale.

In an → optical system, the space defined by the totality of → image points. The corresponding points in image space and → object space are called → conjugate points.

See also: → image; → space.

A device for amplifying faint images by electronic means. Electrons, released when the incident radiation forms a pattern on a photocathode, are accelerated by a magnetic field so that they form a second, brighter image when they strike a phosphor screen.

See also: → image; → tube.

An electronic device which records images.

See also: → image; → -er.

1. The formation of mental images, figures, or likenesses of things, or of such images collectively.
   

   2. Pictorial images, as in works of art (Dictionary.com).

See also: Noun from → imager.

Capable of being imagined or conceived.

See also: → imagine; → -able.

1. Existing only in the imagination.
   

   2. Math.: → imaginary number.

See also: → imagine; → -ary.

A number that is or can be expressed as the square root of a negative number; thus √ -1 is an imaginary number, denoted by i; i² = - 1.

See also: → imaginary; → number.

1. The faculty of imagining, or of forming mental images or concepts of what is not actually present to the senses.
   

   2. The action or process of forming such images or concepts (Dictionary.com).

See also: → imagine; → -tion.

Characterized by or bearing evidence of imagination (Dictionary.com).

See also: → imagination; → -ive.

1. To form a mental image of (something not actually present to the senses).
   

   2. To think, believe, or fancy.
      

   3. To assume; suppose.
      

   4. To conjecture; guess (Dictionary.com).

Etymology (EN): M.E. imaginen, from M.Fr. imaginer “sculpt, carve, paint; decorate,” from L. imaginari “to form a mental picture, picture to oneself, imagine,” from imago “an image, a likeness,” from stem of imitari “to copy, imitate” (from PIE root *aim- “to copy”).

Etymology (PE): Vinârdan, from vin, short for vine, → image, + ârdan, short for âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

The visual representation of an astronomical body using a two-dimensional detector and computerized techniques.

Etymology (EN): From → image + → -ing.

Etymology (PE): Tasvirgari, from tasvirgar agent noun from tasvir→ image + -gar
from kar-, kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “makes;” cf. Skt. kr- “to do, to make;” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).

The method used to detect very brief flashes of → Cherenkov radiation generated by the → cascade shower of → relativistic charged particles produced when a very high-energy → gamma ray (in the range 50 GeV to 50 TeV) strikes the atmosphere at a typical altitude of 10 km. Owing to this technique, it possible to discriminate cosmic gamma rays from the cosmic ray background and to determine their energy and source direction. More specifically, the incoming gamma-ray photon undergoes → pair production in the vicinity of the nucleus of an atmospheric molecule. The electron-positron pairs produced are of extremely high energy and immediately radiate in a → bremsstrahlung process. This radiation is itself extremely energetic, with many of the photons undergoing further pair production. A cascade of charged particles ensues which, due to its extreme energy, produces a flash of Cherenkov radiation lasting between 5 and 20 nano-seconds. The total area on the ground illuminated by this flash corresponds to many hundreds of square meters, which is why the effective area of IACT telescopes should be large.

See also: → imaging; → atmospheric; → Cherenkov; → technique.

A detector with two-dimensional capability, such as a CCD.

See also: → image; → → scale.

1. Occurring or accomplished without delay; following or preceding without a lapse of time. → instant.
   

2. Having no object or space → intervening; without intervening medium or agent; direct (Dictionary.com).

Etymology (EN): M.E. immediat, from O.Fr. immediat, from L.L. immediatus “without anything between,” from → in- “not, opposite of,” + mediatus, p.p. of mediare “to be in the middle,” from L. medius “middle,” → medium.

Etymology (PE): Âni, from ân loan from Ar. ân “time, a short time.”
Amadim, literally “with nothing interposed,” from the negation prefix → a- + madium, → medium.

To plunge into or place under a liquid; dip; sink (Dictionary.com).

See also: → in- + merge, → submerge.

The disappearance of a star, planet, moon, or other body at the beginning of an → occultation or → eclipse. Also called → ingress.

See also: → immerge.

To come to a country of which one is not a native, usually for permanent residence.

See also: → in-; → migrate.

A collision between two bodies. In the case of solar system objects,
when one is much smaller than the other (like a meteoroid colliding with the Earth), a crater may be produced on the larger body.

Etymology (EN): From L. impactus, p.p. of impingere “to drive into, strike against,” from → in- “in” + pangere “to fix, fasten.”

Etymology (PE): Barxord, verbal noun of barxordan “to collide, clash, dash against each other,” from bar- “on, upon, up” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”)

• xordan “to hit, strike,” originally “to eat, drink, devour,” and by extension “to destroy,” from Mid.Pers. xvardan “to eat, enjoy (food),” Av. x^var- “to consume, eat;” Laki dialect hovârden “to eat;” Proto-Iranian *huar- “to consume, eat.”

A depression produced by the collision of a meteorite, asteroid, or comet with the surface of a planet or a satellite. Impact craters are the most characteristic surface features of solar system rigid bodies. They range in size up to hundreds or thousands of kilometers (where the impacts create giant basins as on the Moon, Mars, and Mercury).

See also: → impact; → crater.

An → atmospheric escape mechanism that occurs where atmospheric gases are expelled en masse as a result of large body impacts, such as the cumulative effect of asteroids hits (see, e.g., Catling, D. C. and Kasting, J. F., 2017, Escape of Atmospheres to Space, pp. 129-167. Cambridge University Press).

See also: → impact; → erosion.

A collision between two celestial objects, specially solar system bodies, with considerable consequences. Impact events involve release of large amounts of energy. Some examples are the 1908 Siberian → Tunguska event by a → comet, the → Barringer Crater, and the collision of an → asteroid with Earth 65 million years ago, which is thought to have led to the extinction of the dinosaurs and other species of the → Cretaceous-Paleogene period.

See also: → impact; → event.

The danger of collision with Earth posed by solar system small bodies that pass near our planet. These objects include → near-Earth asteroids and nuclei of → comets. See also: → near-Earth object, → impact crater, → Torino scale, → Palermo scale, → Space Situational Awareness.

See also: → impact; → hazard.

The loss of orbital electrons by an atom of a crystal lattice which has undergone a high-energy collision.

See also: → impact; → ionization.

1. A measure of the distance by which a collision fails being frontal.
   

2. In → gravitational lensing, the distance of closest approach of the light path to the → lensing object.
   

3. In → rainbows, the displacement of the → incident from an axis that passes through the center of the water droplet.

See also: → impact; → parameter

The enormous drop in temperature and the related effects of the shrouding of Earth with soot and dust particles after the planet is struck by a sizable comet or asteroid. Such a phenomenon is believed to have killed off the dinosaurs 65 million years ago.

See also: → impact; → winter.

A general term used for all rocks affected by, or produced by, the → shock waves and other processes generated by hypervelocity → meteorite → impact events. Impactites occur in and around the → impact crater, typically as individual bodies composed of mixtures of melt and rock fragments, often with traces of meteoritic material.

See also: → impact; → -ite.

A natural impacting body, such as a comet, asteroid, or planet. It can also be a space probe designed to collide with an astronomical body in the solar system.

Etymology (EN): Impactor, from → impact + -or a suffix forming agent nouns.

Etymology (PE): Barxordgar, from barxord, → impact,

• -gar agent suffix, from kar-, kardan “to do, to make” (Mid.Pers. kardan, O.Pers./Av. kar- “to do, make, build,” Av. kərənaoiti “makes,” cf. Skt. kr- “to do, to make,” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).

1. To give, convey, or grant from or as if from a store.
   

2. To communicate the knowledge of; disclose.

Etymology (EN): M.E., from O.Fr. impartir, from L.L. impartire “to share in, divide with another, communicate,” from assimilated form of → in- “into, in” + partire “to divide, → part.”

Etymology (PE): Darpârdan, from dar-, → in-, + pâr, → part, Mid.Pers. pârag “part, portion; gift, offering;” Av. pāra- “debt,” from par- “to remunerate, equalize; to condemn;” PIE *per- “to sell, hand over, distribute; to assign;” + -dan infinitive suffix.

General: The ratio of a quantity with the nature of a force to a related quantity with the nature of a current.
Electricity: The apparent opposition in an electrical circuit to the flow of an alternating current that is analogous to the actual electrical resistance to a direct current and that is the ratio of effective electromotive force to the effective current

Etymology (EN): From impede, from L. impedire “to entangle,” literally “to shackle the feet,” from in- “in” + pes (gen. pedis) “foot” + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.

Etymology (PE): Pâgiri, verbal noun of pâgir “impedder, impeded; hinderer, hindered,” from pâ “foot, step” (from
Mid.Pers. pâd, pây; Av. pad- “foot;” cf. Skt. pat; Gk. pos, gen. podos; L. pes, gen. pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-) + gir present stem of gereftan
“to take, seize” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”).

Latin verb meaning “to command, rule, reign.”

Etymology (EN): L. imperare “to command, give orders, exercise authority,” from → in- “into, in” + parare “to make ready, supply, order,” related to parire “produce, give birth to,” from PIE root *pere- “to produce, procure;” cf. Skt. prthukah “child, calf, young of an animal;” Gk. poris “calf, bull;” Czech spratek “brat, premature calf;” Lith. periu, pereti “to brood;” O.H.G. farro, Ger. Farre, Du. varre “bull,” O.E. fearr “bull;” see below for possible Iranian cognates.

Etymology (PE): Parmâtidan, from BMP plm’(d)y “to command, order,” Sogd. framat- “to command,” variants of farmudan, farmâyidan “to command, to order,” ultimately from prefixed Proto-Ir. *fra-maH-, from *maH- “to measure,” → experiment.

1a) A command or order.

1b) → imperative case.

2a) Absolutely necessary or required; extremely important.

2b) Of the nature of or expressing a command; commanding.

Etymology (EN): From L.L. imperativus “pertaining to a command,” from imperat-, p.p. stem of → imperare “to command.”

Etymology (PE): Parmât, noun from present stem of parmâtidan, → imperare; parmâtii, adj. from parmât.

The grammatical mood of a verb that expresses a command or a request, as in close the door!.

See also: → imperative; → case.

In an imperative manner.

See also: Adverb from → imperative; → -ly.

Not perfect; faulty or incomplete.

See also: → in-; → perfect.

A fault, flaw, or undesirable feature; the state or condition of being imperfect.

See also: → in-; → perfection.

Of, relating to, or suggestive of an empire or a sovereign, especially an emperor or empress (TheFreeDictionary).

See also: Adjective of → empire.

1. The extension of a nation’s authority by territorial acquisition or by the establishment of economic and political dominance over other nations.
   

   2. A political doctrine or system promoting such extension of authority (TheFreeDictionary.com).

See also: → imperial; → -ism.

1. General: Something implied; the act of implying.
   

2. A statement that follows from other given statements. For ex., an implication of x = -1 is that x² = 1.
   

3. A proposition found from two given propositions by connecting them in the form “If …, then …”. The first statement is the antecedent (or hypothesis) and the second the consequent (or conclusion).

Etymology (EN): From L. implicationem “interweaving, entanglement,” from implicatus, p.p. of implicare “involve, entangle, connect closely,” from → in- “in” + plicare “to fold,” → explain.

Etymology (PE): Dartâheš, verbal noun of dartâhidan “to imply,” from dar-, → in- + tâhidan “to fold, ply,” → explain.

1. General: Implied, rather than expressly stated.
   

2. Math.: → implicit function.

Etymology (EN): From L. implicitus, variant of implicatus, p.p. of implicare, → implication.

Etymology (PE): Dartâhi, from dartâh present stem of dartâhidan,
→ implication, + -y adj. suffix.

A function which contains two or more variables that are not independent of each other. An implicit function of x and y is one of the form f(x,y) = 0, e.g., 4x + y² - 9 = 0. See also → explicit function.

See also: → implicit; → function.

To collapse, or cause to → collapse, inward → violently. Opposite of → explode.

Etymology (EN): Implode, from → in- + (ex)plode, from
L. plaudere “to clap, beat,” of uncertain origin.

Etymology (PE): Forukaftidan, from foru- “down, downward; below; beneath” (Mid.Pers. frôt “down, downward;” O.Pers. fravata “forward, downward;” cf. Skt. pravát- “a sloping path, the slope of a mountain”) + 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”).

A violent inward collapse; the act of imploding; opposed to → explosion.

See also: Verbal noun of → implode.

1. To involve or indicate by inference, association, or necessary consequence rather than by direct statement .
   

2. To contain potentially.
   

3. To express indirectly (Merriam-Webster.com).

See also: Infinitive of → implication.

1a) To bring in (merchandise, commodities, workers, etc.) from a foreign country for use, sale, processing, reexport, or services.

1b) Computers: To bring (documents, data, etc.) into one software program from another.

2. The act of importing or bringing; something that is imported (Dictionary.com).

See also: From im-, variant of → in- + port, → export.

Of great significance or effect.

Etymology (EN): From M.Fr. important, from M.L. importantem, from importare “be significant in,” from importare “bring in,” → in- “into, in” + portare “to carry.”

Etymology (PE): Garin, on the model of Kurd. giring “important,” related to girân, gerân “heavy, important;” Mid.Pers. garân, Proto-Ir. stem *garu-; cf. Av. gouru-; Skt. guru- “heavy, important, venerable;” L. gravis “weighty, serious, heavy,” → gravity.

1. To lay on or set as something to be borne, endured, obeyed, fulfilled, paid, etc.
   

2. To put or set by or as if by authority (Dictionary.com).

Etymology (EN): M.E., from O.Fr. imposer “put, place; impute, charge, accuse,” from → in- “into, in” + poser “put, place,” → position.

Etymology (PE): Barnehâdan, literally “to place on, upon,” from bar-, → on-,

• nehâdan “to put, place,” → compose.

Very impressive because of great size, stately appearance, dignity, elegance, etc. (Dictionary.com).

See also: → impose; → -ing.

1. The laying on of something as a burden or obligation.
   

2. Something imposed, as a burden or duty; an unusual or extraordinarily burdensome requirement or task.
   

3. The act of imposing by or as if by authority (Dictionary.com).

See also: → impose; → -tion.

Not possible; unable to be, exist, happen. Unable to be done, performed, effected.

See also: → in-; → possible.

On who pretends to be what he is not.

Etymology (EN): M.Fr. imposteur, from L.L. impostor, agent noun from impostus, from imponere “to place upon, impose upon, deceive,” from → in- “into, in, on, upon” + ponere “to put place,” → position.

Etymology (PE): Daqalkâr, from daqal “imposture, deceit” + -kâr, agent noun suffix, from kardan, → -or.

Not precise; not exact; vague.

See also: From im-, variant of → in- + → precise.

The quality of lacking → precision.

See also: From im-, variant of → in- + → precision.

1. To press, to apply with pressure, especially to leave a mark.
   

2. To produce a profound effect upon the mind.

See also: → in-; → press.

1. A strong effect produced on the intellect, feelings, conscience, etc.
   

2. The first and immediate effect of an experience or perception upon the mind (dictionary.com).

See also: → press + -ion variant of → -tion.

Capable of being impressed; easily impressed.

See also: → impress; → -able.

1. A style of painting developed in the last third of the 19th century, characterized chiefly by short brush strokes of bright colors in immediate juxtaposition to represent the effect of light on objects.
   

2. A manner of painting in which the forms, colors, or tones of an object are lightly and rapidly indicated.
   

3. A manner of sculpture in which volumes are partially modeled and surfaces roughened to reflect light unevenly (Dictionary.com).

See also: → impression; → -ism.

Having the power to impress, to raise admiration, awe, respect, etc.

See also: → impress; → -ive.

Of a force acting on a body, the → product of the → force and the → time for which it acts. If the force changes with time, the impulse is the → integral of the force with respect to the time during which the force acts, and is
equal to the total change of → momentum produced by the force:

∫F dt = ∫m dv.

Impulse is a → vector quantity.

Etymology (EN): From L. impulsus “a push against, pressure, shock,” p.p. of impellere “to push, strike against, drive forward,” from → in- “into” + pellere “to push, drive.”

Etymology (PE): Tekâné, from tekân “involuntary motion, sudden shaking,” related to tak “rush, quick motion, stroke, blow” (tâxtan, tâzidan “to run; to hasten; to assault”); Mid.Pers. tak “assault, attack;” Av. taka- “leap, run,” from tak- “to run, flow;” cf. Skt. tak- “to rush, to hurry,” takti “runs;” O.Ir. tech- “to flow;” Lith. teketi “to walk, to flow;” O.C.S. tešti “to walk, to hurry;” Tokharian B cake “river;” PIE base *tek^w- “to run; to flow;” → flow.

The vector → impulse of the → resultant force on a particle, in any time interval, is equal in magnitude and duration to the vector change in momentum of the particle:

∫F dt = mv₂ - mv₁.

The impulse-momentum principle finds its chief application in connection with forces of short duration, such as those arising in collisions or explosions. Such forces are called → impulsive forces.

See also: → impulse; → momentum; → principle.

Relating to → impulse, the force which is very large but acts for a very short time.

See also: Impulsive, adj. of → impulse;
→ force.

A substance that is incorporated into a semiconductor material to provide free electrons (n-type impurity) or holes (p-type impurity).

Etymology (EN): Impurity, from im- negation prefix, → in-, + purity, O.Fr. pureté, from L.L. puritatem (nom. puritas) “cleanness, pureness,” from purus “clean;” cf. Av. pūitika- “serving for purification,” Mod.Pers. pâk “clean;” Skt. pavi- “to become clean,” pávate “purifies, cleanses;” O.H.G. fouwen, fewen “to sift;” PIE base *peu- “to purify, cleanse.”

Etymology (PE): Nâžâvi “impurity,” from nâ- negation prefix, → in-, + žâv “pure” + -i noun suffix.