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

The acceleration exerted on the plasma particles according to the → magnetocentrifugal model.

→ magnetocentrifugal model; → acceleration.

A → magnetohydrodynamic model devised to account for the → bipolar jets and → outflows observed around → protostars. Basically, a → poloidal magnetic field is frozen into a rotating → accretion disk. If the angle between the magnetic field lines threading the disk and the rotation axis of the disk is larger than 30°, the plasma can be accelerated out of the accretion disk along the field lines. The field lines rotate at a constant → angular velocity, and as the gas moves outward along the field lines, it is accelerated by an increasing → centrifugal force (magnetocentrifugal acceleration). At some point, when the rotation velocity is about the same as the → Alfven velocity in the gas, the field lines get increasingly wound up by the inertia of the attached gas and a strong → toroidal magnetic field component is generated. The toroidal component is the main agent in collimating the flow into a direction along the → open magnetic field lines. The earliest version of the model was proposed by Blandford & Payne (1982, MNRAS 199, 883). It has two main versions: → X-wind and → disk wind models. See also → magnetorotational instability.

→ magneto-; → centrifugal; → model.

The factor by which the angular diameter of an object is apparently increased when viewed through an optical instrument to that of the object viewed by the unaided eye.

Verbal noun of → magnify.

A thing or device that magnifies.

From → magnify + suffix -ir.

Bozognemâ, agent noun of bozorg nemudan, → magnify.

To increase the apparent size of, as a lens does.

From O.Fr. magnifier, from L. magnificare "esteem greatly, extol," from magnificus "splendid," from magnus "great" + root of facere "to make."

From bozorg "large, magnificent, great" + nemudan "to show." The first element from Mid.Pers. vazurg "great, big, high, lofty;" O.Pers. vazarka- "great;" Av. vazra- "club, mace" (Mod.Pers. gorz "mace"); cf. Skt. vájra- "(Indra's) thunderbolt," vaja- "strength, speed;" L. vigere "be lively, thrive," velox "fast, lively," vegere "to enliven," vigil "watchful, awake;" P.Gmc. *waken (Du. waken; O.H.G. wahhen; Ger. wachen "to be awake;" E. wake); PIE base *weg- "to be strong, be lively." The second element nemudan from Mid.Pers. nimūdan, nimây- "to show," from O.Pers./Av. ni- "down; into," → ni-, + māy- "to measure," → display.
Bozorgidan infinitive from bozorg + -idan.

A lens or lens system that produces an enlarged virtual image of an object placed near its front focal point. According to Enoch (1998, SPIE vol. 3299, p. 424), the earliest lenses identified are from the IV/V Dynasties of Egypt, dating back to about 4,500 years ago (e.g., the eyes of the Louvre statue Le scribe accroupi and other examples located in the Cairo Museum). For more information see → burning sphere.

Magnifying, verbal adj. of → magnify; → glass.

Zarrebin, from zarré "a minute thing," → particle, + bin "seer; to see" (present stem of didan; Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know;" Gk. oida "I know," idein "to see;" L. videre "to see;" PIE base *weid- "to know, to see").

The ratio between the focal lengths of the objective and ocular in a telescope.

Magnifying, verbal adj. of → magnify; → power.

1) Readily perceived by the eye or the understanding; evident; obvious; apparent; plain.
2) To make clear or evident to the eye or the understanding; show plainly (Dictionary.com).

M.E., from O.Fr. manifest "evident, palpable," or from L. manifestus "plainly apprehensible, clear, apparent, evident;" "proved by direct evidence;" "caught in the act," probably from manus "hand," + -festus "struck; (able to be) seized."

From Torbat-Heydariye-yi nemusâr "evident, conspicuous, visible," from nemu-, nemudan "to show, display" from Mid.Pers. nimūdan, from ne- "down; into;" O.Pers./Av. ni- "down; below; into," → ni-, + mu- (as in âz-mu-dan, â-mu-dan, far-mu-dan, pey-mu-dan, etc.); Av. mā(y)- "to measure," → display, + -sâr a suffix of state, position, similarity.

1) An act of manifesting.
2) The state of being manifested.
3) Outward or perceptible indication; materialization.
4. A public demonstration, as for political effect (Dictionary.com).

Verbal noun of → manifest; → -tion.

A → topological space in which every point has a → neighborhood which resembles → Euclidean space (Rⁿ), but in which the global structure may be different. An example of a one-dimensional manifold would be a circle; if you zoom around a point the circle looks locally like a line (R¹). An example of a two-dimensional manifold would be a sphere; a small portion looks locally like a plane (R²). See also → flat manifold.

O.E. monigfald (Anglian), manigfeald (W.Saxon) "varied in appearance," from manig "many" + -feald "fold."

Baslâ, from bas "many, much" (Mid.Pers. vas "many, much;" O.Pers. vasiy "at will, greatly, utterly;" Av. varəmi "I wish," vasô, vasə "at one's pleasure or will," from vas- "to will, desire, wish") + lâ "fold."

The portion of the isotope shift which results from the difference between the nuclear masses of different isotopes.

→ mass; → shift.

The average amount of time an unstable radioisotope exists before it decays, It is equal to 1.44 times the half-life.

→ mean; → life.

An act or instance of modifying; the state of being modified; partial alteration.

Verbal noun of → modify.

A modification of the Julian Date, representing the number of days that have elapsed since midnight (instead of noon) at the beginning of Wednesday November 17, 1858. MJD = JD - 2,400,000.5 The reason for adopting that date is the fact that the Julian Day 2,400,000 just happens to be November 17, 1858.

→ modify; → Julian date.

A modification of the Newton's law of gravitation below a critical acceleration of about 1.2 x 10^-8 cm s^-2, where the gravitational force scales as 1/r instead of 1/r². Originally put forward to describe the rotation curves of galaxies with no need to assume any dark matter, MOND is now tested at larger cosmological scales (Milgrom, M. 1983, ApJ, 270, 365).

→ modify; → Newtonian dynamics.

A quantity defined as Π = (dM/dt) v_∞ R^0.5 for a star with radius R having a wind with → terminal velocity v_∞ and a → mass loss rate dM/dt. There is a tight linear relation between the modified wind momenta and the stellar luminosities for → Population I→ O stars. See also → wind momentum.

→ modify; → wind; → momentum.

In data processing, a quantity used to alter an instruction in a prescribed way to produce the instruction actually obeyed.

Agent noun of → modify.

To change somewhat the form or qualities of; alter partially; amend.
To reduce or lessen in degree or extent; moderate; soften:

From O.Fr. modifier, from L. modificare "to impose a rule or pattern, regulate, restrain," from modus "measure, rhythm, song, manner" PIE base *med-/*met- "to measure, limit, consider, advise, take appropriate measures" + root of facere "to make"

Vâtarzidan, from vâ- prefix denoting "reversal, opposition; separation; repetition; open; off; away" (variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] "away, from;" Av. apa- [pref.] "away, from," apaš [adv.] "toward the back;" cf. Skt. ápāñc "situated behind") + tarz "mode, manner" + -idan infinitive suffix.

A mixing process in a → fluid caused by the → random relative motions due to → Brownian motion of the individual particles. See also → eddy diffusion.

→ molecular; → diffusion.

A system of → spectral classification introduced in 1943 by William W. Morgan (1906-1994), Philip C. Keenan (1908-2000), and Edith M. Kellman (1911-2007) at Yerkes Observatory. Also known as the MK (or MKK) classification or the → Yerkes system.

Named after the two main astronomers, as above; → classification.