An Etymological Dictionary of Astronomy and Astrophysics

For the specific purpose at hand, as opposed to a general solution; also, by extension, improvised or impromptu.

Etymology (EN): From L. ad “to, with, in,” cf. Skt. adhi “near,” PIE *ad- “to, near, at.”

Etymology (PE): Pad im, from Mid.Pers. pad “to, at, for, in” (Mod.Pers. bé “to, for, in, on, with, by”);
O.Pers. paity “agaist, back, opposite to, toward, face to face, in front of;” Av. paiti “to, toward, in, at;” cf.
Skt. práti “toward, against, again, back, in return, opposite;” Pali pati-; Gk. proti, pros “face to face with, toward, in addition to, near;” PIE *proti)

• Mid.Pers. im “this;” from Old.Pers./Av. ima “this;” Skt. imá; cf. Lori (Laki) im “this side.” The Mid.Pers. im occurs in Mod.Pers. as em- in emruz “today,” emšab “tonight,” and emsâl “this year.”

Addition of adjustments to a theory to save it from being falsified by compensating for anomalies not anticipated by the theory in its unmodified form. Theories that rely on continual, ad hoc adjustments are distrusted.

See also: → ad hoc; → hypothesis.

A fallacious objection to an argument or factual claim by appealing to a characteristic or belief of the person making the argument or claim, rather than by addressing the substance of the argument or producing evidence against the claim (wiktionary).

Etymology (EN): Literally “to a man,” from → ad- “to,” + hominem, accusative of homo “man,” → human.

Etymology (PE): Pad mart, literally “to a man,” from pad “to,” → ad hoc, + mart, → man.

Prefix meaning “to, toward, addition to, near,” from L. ad “to, toward.” It is modified to ac- or af- or ag- or al- etc. according to the following consonant.

Etymology (EN): Cognate with E. at, from O.E. æt “near, by, at”; compare with O.N., Goth. at, O.Fris. et, O.H.G. az, Skt. adhi “near,” PIE *ad- “to, near, at”.

To make suitable to or fit for a specific use or situation.

Etymology (EN): From M.Fr. adapter, from L. adaptare “adjust,” from ad- “to” + aptare “join,” from aptus “fitted.”

Etymology (PE): Niyâvidan from Mid. Pers. niyâw “apt, suitable, appropriate” + -idan verb making suffix.

Capable of adapting or of being adapted.

See also: → adapt + → -able.

1. The act or process of adapting.
   
2. The state of being adapted.

See also: → adapt.

Physiological process whereby the eye adjusts its sensitivity for different levels of illumination.

See also: → adaptation, → eye.

1. General: One that adapts.
   An appliance for connecting objects of different sizes or designs in an apparatus.
   
2. Astro.: A device that allows an observing instrument (imaging camera, spectrograph) to be mounted on a focus (e.g. Cassegrain) of a telescope.

See also: → adapt + → -er.

Same as → adaptation.

See also: → adaptation.

1. Relating to or exhibiting adaptation.
   
2. Capable of adapting or of being adapted. → adaptive optics; → adaptive optics system; → extreme adaptive optics.

See also: → adapt; → -ive.

A type of → algorithm that dynamically achieves high → resolution in localized regions of multidimensional → numerical simulations. AMR provides a higher → accuracy solution at lower costs, through an automatically → optimal distribution of → grid points for the computation region. It relies on locally refined mesh or mesh patches to increase the resolution of an underlying coarse mesh only where needed. It can alleviate some of the complexities of the generation of high quality grid and reduce the number of → iterations of “trial-and-error” between the grid generation and solution required for tailoring the grid to the specification of a problem. Thus, it can offer orders of magnitude saving in computational and storage costs over an equivalent uniformly refined mesh. AMR was originally developed for → inviscid, → compressible flow (Berger et al., 1984, Adaptive Mesh Refinement for Hyperbolic Partial Differential Equations. J. Comp. Phy., 53, 484). It has been extended to solve → Navier-Stokes equations, time dependent problems and more. Several AMR techniques have been developed and applied to compressible flow fields to capture characteristics at the strong gradient or discontinuous regions requiring higher space resolution, such as regions involving → shock waves, vortices (→ vortex), and → wakes
(see, e.g., Qingluan Xue, “Development of Adaptive Mesh Refinement Scheme and Conjugate Heat Transfer Model for Engine Simulations” (2009), Iowa State Univ., Graduate Theses and Dissertations, Paper 10678).

See also → Smoothed Particle Hydrodynamics.

See also: → adaptive; → mesh; → refinement.

A technique for improving the → image quality of a telescope against → atmospheric turbulence in which image distortions are compensated by high-speed changes in the shape of a small, thin mirror. → wavefront; → wavefront distortion; → wavefront correction; → Strehl ratio; → tip-tilt mirror, → Shack-Hartmann wavefront sensor, → active optics.

See also: → adaptive; → optics.

An → adaptive optics instrument used on the → European Southern Observatory (ESO) 3.6-m telescope at La Silla. It was an upgraded version of COME-ON-PLUS, the → Very Large Telescope (VLT) adaptive optics prototype.

It had 52 → actuators and performed corrections of the mirror 200 times per second. The reference → wavefront was sensed in the → visible. The observation was done in the → near-infrared (1-5 μm).

See also: → adaptive; → optics; → near-infrared; → system.

An → optical system that uses → adaptive optics.

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

1. To unite or so as to bring about an increase.
   

2. To increase a number by another number using addition, which leads to a → sum.

Etymology (EN): M.E. adden, from L. addere “add to, join,” from → ad- “to” + -dere combining form meaning “to put, place,” from dare “to give, grant,” from PIE base *do- “to give” (cf. Av. and O.Pers. dâ- “to give, grant, yield,” Av.
dadâiti “he gives,” Skt. dadâti “he gives,” Gk. didomi “I give,” L. do “I give”).

Etymology (PE): Bardâyidan, from bar- “on; up; upon; in, into; at; forth,” → on-, + O.Pers./Av. dā- “to give, grant, put,” dadāiti “he gives;” Mid.Pers./Mod.Pers. dâdan “to give, put”
(cf. Skt. dadáti “he gives;” Gk. tithenai “to place, put, set,” didomi “I give;”
L. dare “to give, offer;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do;” PIE base *dhe- “to put, to do”)

• -y-, epenthetic vowel, + infinitive suffix -idan.
  Afzudan, → increase.

A number or quantity to be added to another. In the expression 5 + 3, both 5 and 3 are addends.

Etymology (EN): From L. addendus “that which is to be added,” → add.

Etymology (PE): Bardâyé, from present stem bardây-,
→ add, + noun forming suffix -é.

The operation of combining two or more quantities to obtain a third quantity called their → sum. The result of adding.

See also: Verbal noun of → add.

The → plus sign +. It is believed to be a shortened form of the letters e and t in the L. word et, which, in early German manuscripts was the term for addition. The signs + and - were first used by Johann Wiedmann in 1489.

See also: → addition; → sign.

1. Involving → addition.
   

2. Something added to a substance to alter or improve it.

Etymology (EN): From L. additivus “added, annexed,” from p.p. stem of addere, → add; → -ive.

Etymology (PE): 1) Related to bardâyeš, → addition; 2) from bardây- prsent stem of bardâyidan, → add,

• -é nuance suffix.

Color created by mixing light rays of different colors. Combining all the color rays of light results in white light.
See also → subtractive color.

See also: → additive; → color.

The number which can be added to any other number without changing the magnitude of that number: zero. → multiplicative identity.

See also: → additive; → identity.

If E₁, E₂, …, E_n
are n → mutually exclusive events, then the probability of occurrence of at least one of them is the sum of their individual probabilities: P(E₁ + E₂ + … + E_n) = P(E₁) + P(E₂) + … + P(E_n).

See also: → additive; → law; → probability.

A binary star, in the constellation → Canis Major, 470 → light-years distant from Earth. The main star possesses an apparent magnitude of +1.5 and belongs to the spectral classification B2 II. The +7.5 magnitude companion star is 7’’.5 apart from the main star.

Etymology (EN): Adhara, from Ar. adhârâ “virgins,” plural of adhrâ’ “virgin”.

Etymology (PE): Azârâ, from Ar. Adhara.

1. To stay attached; stick fast; cling.
   

2. Physics: (of two or more dissimilar substances) to be united by a molecular force acting in the area of contact (→ adhesion).

Etymology (EN): From M.Fr. adhérer or directly from L. adhaerere “to stick to,” from → ad- + haerere “to stick.”

Etymology (PE): Âdusidan, from intensive/nuance prefix â-

• dusidan (Dehxodâ) “to stick, to adhere,” maybe related to Proto-Ir. *dauc- “to sew;” Pers. duxtan, duz- “to sew.”

1. The act or state of adhering; adhesion.
   

2. The quality of adhering; steady devotion, support, or attachment (Dictionary.com).

See also: → adhere + -ence, → -ance.

1. A person who follows or upholds a leader, cause, etc.; supporter; follower.
   

2. Sticking; clinging; adhering (Dictionary.com).

Etymology (EN): From O.Fr. adherent or directly from L. adhaerentem pr.p. of adhaerere “to stick to,” → adhere.

Etymology (PE): Âdusandé, from âdusidan, → adhere.

1. The act or state of adhering; state of being adhered or united.
   

2. Steady or devoted attachment, support, etc.; adherence.
   

3. Physics: The molecular force of attraction in the area of contact between unlike bodies that acts to hold them together (Dictionary.com). See also → cohesion.

See also: Verbal noun from → adhere; → -tion.

1. Of or pertaining to the molecular force → adhesion.
   

2. A substance used for sticking objects or materials together; glue.

See also: Adjective from → adhere.

The force of → attraction between molecules of different substances; for example, the force between the molecules of a solid and a liquid. When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the surface. This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.

See also: → adhesive; → force.

A → late-type → giant star of → spectral type K0-IIIb in → Andromeda. Other designations: ξ
(Xi) Andromedae, HR 390, and HD 8207. → Visual magnitude = 4.88, B - V = +1.08.

See also: From Ar. Al-dhayl “skirt of a garment; tail.”

A → thermodynamic process that occurs without → loss or → gain of → heat.

See also:

→ adiabatic change, → adiabatic index, → adiabatic initial conditions, → adiabatic phase, → adiabatic process, → adiabatic shock, → adiabatic temperature gradient, → superadiabatic temperature gradient.

Etymology (EN): From Gk. adiabatos “impassable,” from a- “not” + diabatos “passable,” from diabainein “to go across,” from dia- " through" + bainein “to go.”

Etymology (PE): Bidarrow from bi- “not; without” + darrow “way out,” from dar “out” + row “to go, going,” from raftan “to go.”

A change taking place in a system that has perfect thermal insulation, so that heat cannot enter or leave the system and energy can only be transferred by work.

See also: → adiabatic; → change.

Of a gas, the ratio of its → specific heat at constant pressure to its specific heat at constant volume: γ = C_P/ C_V.

See also: → adiabatic; → index.

The assumption whereby the density fluctuations in the very → early Universe would be produced by compressing or decompressing of all components of a homogeneous Universe. The adiabatic initial conditions lead to coherent oscillations in the form of peaks in the → temperature anisotropy spectrum. See also → acoustic peak, → baryon acoustic oscillation.

See also: → adiabatic; → initial; → condition.

Same as the → Sedov-Taylor phase.

See also: → adiabatic; → phase.

A → thermodynamic process in which no → heat is supplied to or rejected from a system. → polytropic process.

See also: → adiabatic, → process.

A → shock wave without → radiative cooling. The term “adiabatic” refers to the fact that no → heat is removed during shock.

See also: → adiabatic; → shock.

The temperature gradient defining the → radiative equilibrium
condition in a region. It is expressed as: dT/dr = (1 - 1/ γ)((T / P)(dP / dr), where T and P are temperature and pressure, dT / dr and dP / dr temperature and pressure gradients respectively, and γ = C_P / C_V.
For radiative equilibrium to be stable against → convection, the actual temperature gradient must be less than the adiabatic temperature gradient, i.e. |dT /dr|_rad < |dT /dr|_ad. See also → Schwarzschild’s criterion.

See also: → adiabatic; → temperature; → gradient.

In grammar, a word that qualifies, describes, or quantifies a noun.

Etymology (EN): M.E., from O.Fr. adjectif, from L. adjectivum “that is added to (the noun),” neuter of adjectivus “added,” from p.p. of adicere “to throw or place (a thing) near,” from → ad- “to” + iacere “to throw,” → jet.

Etymology (PE): Zâbé, from zâb “attribute, quality” (Dehxodâ); probably related to zib “beauty, adornment,” zibâ “beautiful, adorned,” zivar “ornament,” zab “easy; gratis; right, direct;” from Proto-Ir. *zai- “to adorn, to equip.”

1. To be close to or in contact with.
   

2. To attach or append (dictionary.com).

Etymology (EN): M.E., from O.Fr. ajoindre“join together, unite,” from L. adjungere “fasten on, harness, join to,” from → ad- “to” + jungere “to bind together,” cognate with → yoke.

Etymology (PE): Âbandidan, âbanidan, from prefix â- + band, vand, bastan, in dialects contracted to ban-, van- “to bind, attach,” → band,

• -idan infinitive suffix.

Literally “joined to.” → adjoint matrix.

See also: → adjoin.

The → transpose of a → matrix in which each → element is replaced by its → cofactor. Same as → conjugate transpose and → Hermitian conjugate.

See also: → adjoint; → matrix.

1. To change (something) so that it fits, corresponds, or conforms; adapt; accommodate.
   

2. To put in good working order; regulate; bring to a proper state or position (Dictionary.com).

Etymology (EN): M.E. ajusten, “to correct, remedy; arrange, settle, compose,” from M.Fr. adjuster, O.Fr. ajouter “to join,” from L.L. adjuxtare “to bring near,” from L. → ad- “to” + juxta “next,” related to jungere “to join,” from PIE *yeug- “to join,” → conjugate, akin to E. → yoke.

Etymology (PE): Barjutidan, from prefix bar-, → on-,

• Kurd. Soriani jut, jot “pair, couple, twin,” Aftari jot “yoke,” classical Pers. yuq, → yoke.

The act of adjusting.

See also: Verbal noun of → adjust.

1. To choose or take as one’s own; make one’s own by selection or assent.
   

2. To take and rear (the child of other parents) as one’s own child, specifically by a formal legal act.
   

3. To vote to accept (Dictionary.com).

Etymology (EN): M.E., from M.Fr. adopter, from L. adoptare, from → ad-

• optare, → opt.

Etymology (PE): Baroptidan, on the model of bargozidan “to choose,” from bar- “on, up, upon, in,” → on-,

• optidan, → opt.

The act of adopting. The state of being adopted.

See also: → adopt; → -tion.

Of or involving adoption. Acquired or related by adoption.

See also: → adopt; → -ive.

The second innermost known satellite of Jupiter, whose orbit is situated at a distance of about 129 000 km from the planet, and its orbital period is of 0.298 days; also known as Jupiter XV. Adrastea is 25 x 20 x 15 km in size.

Etymology (EN): In Gk. mythology, Adrastea was the daughter of Zeus and Ananke and the distributor of reward and punishments.

To take up and hold another substance on the surface.

See also: → adsorption.

1. A material that can hold or condense molecules of another substance on its surface by adsorption.
   
2. Relating to or capable of adsorption.

Etymology (EN): From → adsorb + →-ent.

Etymology (PE): Baršamandé, from baršamidan, → adsorb,

• -andé.

A process in which a layer of atoms or molecules of one substance forms on the surface of a solid or liquid. → absorption, → desorption, → sorption.

Etymology (EN): Adsorption from ad- “to” + sorption, from L. sorbere “to suck,” → absorption.

Etymology (PE): Baršam, from bar- “on, upon” + šam “to drink, sip,” → absorption.

1. A person who is fully grown or developed or of age.
   

2. Having attained full size and strength; grown up; mature. A person who has attained the age of maturity as specified by law (Dictionary.com).

Etymology (EN): From L. adultus “grown up, mature, adult, ripe,” p.p. of adolescere “to grow up, mature,” from → ad- “to” + alescere “be nourished,” from alere “to nourish.”

Etymology (PE): Bornâ, from Mid.Pers. purnây- “adult;” Av. pərənāyu- “adult, old;” (Baluchi warnâ “adolescent”), literally “of full age,” from pərəna-, → full, + āyu- “age,” → aeon.

The slow rotation of the major axis of a planet’s orbit in the same direction as the revolution of the planet itself, due mainly to gravitational interactions with other planets. The perihelion of the planet Mercury advances about 9’.6 per century. The bulk of the advance was accounted by perturbations from other planets. However, a remaining small advance, by 43’’ per century, was eventually explained as an effect predicted by Einstein’s theory of → general relativity. In the case of close binary stars, the advance of pericenter may additionally be caused by mass transfer and the stars’ distorted (elliptical) shapes. Advance of perihelion (or pericenter) is also known as → apsidal motion.

Etymology (EN): Advance, from O.Fr. avancer “move forward,” from V.L. *abantiare, from
L.L. abante “from before,” from ab- “from” + ante “before,” PIE *ant- “front, forehead;” → perihelion.

Etymology (PE): Pišraft “advance,” from piš “forward; in front; before,” Mid.Pers. peš

• raft “going; walk, travel,” from raftan “to go.”

A wave that travels backward in time according to Maxwell’s electromagnetic theory; it arrives before it is transmitted. → Maxwell’s equations have two solutions, the normal solution
describes the ordinary waves, called → retarded waves, traveling forward in time. However, no advanced waves have ever shown up in any experiment. The advanced solutions of Maxwell’s equations are usually simply discarded as “unphysical.”

Etymology (EN): Advanced, adj. from advance, →
advance of perihelion; → wave.

Etymology (PE): Mowj, → wave; pišras “advanced,” from piš “before,” Mid.Pers. peš

• ras “arriving,” from rasidan “to arrive,” Mid.Pers. rasitan, O.Pers./Av. rasa- present stem of ar- “to move, go or come toward,” cf. Skt. ar-, rcchati.

1. Geology: The process of transport of a quantity by the velocity field due to the movement of a fluid. Advection differs from → convection, which describes thermally driven circulation.
   

2. Meteorology: The predominantly horizontal, large-scale motions of the atmosphere. In contrast, convection describes the predominantly vertical, locally induced motions.

Etymology (EN): From L. advecti “act of conveying,” from advectus, past participle of advehere “to carry,” from ad-, “to” + vehere “to carry, bring;” Skt. vah-, vahati “to carry, conduct, guide,” Av. vaz-, vazaiti “to guide, lead”; PIE *wegh- “to go, transport in a vehicle”.

Etymology (PE): Pahnbaz from pahn “flat, wide, → broad,”

• baz “to carry,” → evection.

The first term on the right side in the → induction equation.

See also: → advection; → term.

Adj. from → advection.

A word that serves to qualify a verb, an adjective, another adverb, or an entire sentence. More specifically, adverbs indicate manner, time, place, cause, or degree, and answer questions such as “how,” “when,” “where,” “how much.”

Etymology (EN): From L.L. adverbium “adverb,” literally “that which is added
to a verb,” from → ad- “to” + verbum “word, → verb,” a translation of Gk. epirrhema “adverb,” from → epi- “upon, on” + rhema “verb.”

Etymology (PE): Apivâz, from api-, → epi-, + vâz “word,” → verb.

1. A person, group, or force that opposes or attacks; opponent; enemy; foe.
   

2. A person, group, etc., that is an opponent in a contest; contestant (Dictionary.com).

Etymology (EN): M.E. adversaire; O.Fr. adversaire “opponent, adversary, rival,” from L. adversarius “opposite, hostile, contrary,” from adversus “turned against,” from → ad- + verse, → universe.

Etymology (PE): Hamestâr, from Mid.Pers. hamestâr “adversary,” from Av. hamaēstar-, from ha-, → com-, + maēd- “to bring down, to suppress.”