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

An acceleration that results from the vector addition of two or more distinct accelerations.

→ resultant; → acceleration.

A single force which has the same effect as all other applied forces collectively.

→ resultant; → force.

A slowing down, holding back, or hindrance,

M.E., from M.Fr., from L retardare "to make slow, delay, keep back, hinder," from → re-, intensive prefix, + tardare "to slow."

Dirkard "delay," from dir "slowly, tardily; late" (Mid.Pers. dêr, variants dagr, drâz "long;" (Mod.Pers. derâz "long," variant Laki, Kurdi derež); O.Pers. darga- "long;" Av. darəga-, darəγa- "long," drājištəm "longest;" cf. Skt. dirghá- "long (in space and time);" L. longus "long;" Gk. dolikhos "elongated;" O.H.G., Ger. lang; Goth. laggs "long;" PIE base *dlonghos- "long") + kard past stem of kardan "to do, to make" (kâr "work," varaint kar (Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build;" Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make").

The act of retarding or state of being retarded. → retardation plate.

Verbal noun of → retard.

Same as → wave plate.

→ retardation; → plate.

The electric or magnetic field that is derived from the → retarded potentials.

Retarded, adj. of → retard; → field.

The → electromagnetic potential at an instant in time and a point in space as a function of the charges and currents that existed at earlier times.

Retarded, adj. of → retard; → potential.

An ordinary electromagnetic wave that goes forward with time. → Maxwell's equations are indifferent to the distinction between past and future. It is therefore permissible for the electromagnetic waves to go backward in time. Forward-in-time waves are called retarded, as they arrive after they are sent by the transmitter. Backward-in-time waves are called → advanced wave.

Retarded, adj. of → retard; → wavel.

The component of a → planispheric astrolabe that is held against the → tympanum by the → horse, but can rotate freely in the → mater around the → pin to simulate the daily movement of the stars in the sky. It is the most characteristic part of the planispheric astrolabe.

From L. rete "net."

Tanandu "spider," from tanidan "to spin," → tension; ankabut "spider," loan from Arab.

A system of intersecting lines which are placed in the focus of the objective of an optical instrument to aid in sighting; aligning, or measuring. Same as reticule.

From L. reticulum "little net," from to ret(e) "net" + -i- + -culum variant of → -ula.

Târbast, from târ "thread, warp, string" (related to tur "net, fishing net, snare," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from tanidan, tan- "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch") + bast "joined, tied," past stem of bastan, vastan "to bind, shut" (O.Pers./Av. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind).

The Net. A small constellation in the southern hemisphere, at 4h right ascension, 62° south declination. It is centred on a group of stars with magnitudes 3.4 to 5 just north-west of the → Large Magellanic Cloud, and about halfway between → Canopus and → Achernar. Abbreviation: Ret; genitive: Reticuli.

L. reticulum "little net," named in 1752 by Abbé Nicolas Louis de Lacaille (1713-1762) to commemorate the reticle, an instrument he used to measure star positions. The constellation was first published by Isaak Habrecht of Strasbourg as the Rhombus, but was renamed by Lacaille as Reticulum Rhomboidalis.

Tur "net, fishing net, snare," related to târ "thread, warp, string," tâl "thread" (Borujerdi dialect), tân "thread, warp of a web," from tanidan, tan- "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch").

The multi-layered, light-sensitive membrane lining the inside of the posterior wall of the eyeball. It contains the rods and cones that receive an image from the lens and send it to the brain through the optic nerve.

M.L. retina, from L. rete "net," Gerard of Cremona's 12c. translation of Arabic (tabaqa) shabakiyya "net-like (layer)," itself a translation of Gk. amphiblestron used by the famous Greek physician, surgeon, and philosopher Galen (AD c129-c216). This term had two meanings, "a surrounding coat" (of the vitreous) and "a fisherman's net." Galen used the word in the first sense, but when it was translated into Ar. the translator inappropriately chose the second meaning.

Šabakiyé, from Ar. šabakiya, from šabaka, šabakat "a net."

An old galaxy with faint emission lines whose ratios are similar to those of → LINERs, i.e. galaxies with low-ionization nuclear emission-line regions. All galaxies after consuming their → molecular clouds, where stars are formed, follow a "passive" evolution during which their → stellar populations simply get older and older. The old stellar populations contain hot post-→ AGB stars and → white dwarfs which are able to ionize the surrounding gas and produce spectra identical to those of LINERS.

Retired in the sense "withdrawn from or no longer occupied with one's business or profession," p.p. of retire, from M.Fr. retirer "to withdraw (something)," from → re- "back" + O.Fr. tirer "to draw;" → galaxy. The concept of retired galaxies was first proposed by G. Stasińska et al. (2008, MNRAS 391, L29) to name the final stages of galaxies that cease their star forming activity. The word "retired" is also to be taken by opposition to "active" in the sense of "containing an accreting black hole" (like Seyfert galaxies), since liners are often thought to be a scaled down version of Seyfert nuclei.

Bâznešasté "retired," literally "seated back, seated away," from bâz-→ re- + nešasté "seated," p.p. of nešastan "to sit;" Mid.Pers. nišastan "to sit;" O.Pers. nišādayam [1 sg.impf.caus.act.] "to sit down, to establish," hadiš- "abode;" Av. nišasiiā [1 sg.subj.acr.] "I shall sit down," from nihad- "to sit down," from ni- "down, in, into," → ni-, + had- "to sit;" PIE base *sed- "to sit;" cf. Skt. sad- "to sit," sidati "sits;" Gk. hezomai "to sit," hedra "seat, chair;" L. sedere "to sit;" O.Ir. suide "seat, sitting;" Welsh sedd "seat;" Lith. sedmi "to sit;" Rus. sad "garden;" Goth. sitan, Ger. sitzen; E. sit.

1a) The forced or strategic withdrawal of an army or an armed force before an enemy, or the withdrawing of a naval force from action.
1b) The act of withdrawing, as into safety or privacy; retirement; seclusion.
2) To withdraw, retire, or draw back, especially for shelter or seclusion.

Mi.E. retret, from O.Fr., variant of retrait, noun use of p.p. of retraire "to draw back," from L. retrahere, from → re- + trahere "to draw."

Pas-kešidan "to retreat, pull back," from pas, → back, + kašidan "to pull, to draw, to drag," → galaxy.

Moving backward; having a backward motion or direction. → retrograde motion.

M.E., from L. retrogradus "going backward," from retrogradi "move backward," from retro- "backward" + gradi "to go, step."

Pasrow, pasraft, from pas- "back, behind," → back, + row, raft present and past stems of raftan "to go, walk;" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

The orbital motion or rotation of a solar system body in a clockwise direction (East to West) when viewed from the north pole of the ecliptic. It is a motion opposed to the → direct motion of the great majority of solar system bodies.

→ retrograde; → motion.

An object which has a retrograde orbit around its primary.

→ retrograde; → object.

An orbit with an inclination between 90° and 270° such as those of some comets and small asteroids orbiting the Sun.

→ retrograde; → orbit.

A shape of constant width created using an equilateral triangle and three similar circles. The equilateral triangle lies in the first circle with a vertex coinciding with the center of the circle and the sides equal to the circle radius. The centers of the two other circles are located at the two other vertices. The Reuleaux triangle is the intersection of the three circles.

Named after Franz Reuleaux (1829-1905), a German engineer, specialist of analysis and design of mechines; → triangle.

An act or instance of reversing. The state of being reversed. → phase reversal.

From → reverse + → -al.