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

An observation which expands previous observations and aims at obtaining complementary data in particular with other telescopes/instruments.

Follow-up, from follow, from O.E. folgian, fylgan "to follow, pursue," from W.Gmc. *fulg- (cf. O.Fris. folgia, M.Du. volghen, Ger. folgen "to follow") + up, O.E. up, uppe (cf. Du. op, Ger. auf "up, upward"), from PIE base *upo "up from below;" cf. O.Pers./Av. upā; Skt. úpa; Gk. hypo; L. sub, → hypo-; → observation.

Nepâheš, → observation; peygir, from pey "after; step," related to pâ "foot, step, track," → foot, + 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").

A → sunspot that follows the → leader spot. Sunspots tend to appear in groups consisting of one leader and several follower spots. The leader and the follower spots having opposite polarities.

Agent noun of follow, from O.E. folgian, fylgan "to follow, pursue," from W.Gmc. *fulg- (cf. O.Fris. folgia, M.Du. volghen, Ger. folgen "to follow").

Laké, → spot; peyrow "follower," from pey "step; after," related to pâ "foot, step, track," → foot, + row "going; which goes," present stem of raftan "to go, walk, proceed," Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack."

The brightest star (V = 1.17) in the constellation → Piscis Austrinus. Fomalhaut is a white A3 main-sequence star about 25 light-years away. It is encircled by a dust belt (→ debris disk) of about 25 A.U. wide at a radial distance of about 140 A.U.

From Ar. Fam al-Hut (فم‌الحوت) "the fish's mouth," from fam "mouth" + hut "fish."

Famelhut, from Ar. as above; Mâhidahân, from mâhi "fish," from Mid.Pers. mâhik; Av. masya-; cf. Skt. matsya-, Pali maccha- + dahân "mouth;" Mid.Pers. dahân, from Av. zafan-, zafar- "mouth (of Ahrimanic beings)."

An assortment or set of type or characters all of one style and sometimes one size (Merriam-Webster.com).

From M.Fr. fonte "act of founding, casting," from fondre "to melt," so called because all the letters in a given set were cast at the same time (etymonline.com).

Rixtâr, from rixtan "to cast, to pour," → morphology.

1) The terminal part of the vertebrate leg upon which an individual stands.
2) Something resembling a foot in position or use.

M.E., from O.E. fot; cf. O.S. fot, O.N. fotr, Du. voet, O.H.G. fuoz, Ger. Fuß, Goth. fotus "foot;" cognate with Pers. pâ, pây, as below.

Pâ "foot;" Mid.Pers. pâd, pây; Khotanese fad; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; E. foot, as above; PIE *pod-/*ped-.

A preposition used to indicate the object or purpose of an action.

M.E., from O.E. for "before, in the sight of, in the presence of" (source also of Old Saxon furi "before," Old Frisian for, Middle Dutch vore, Dutch voor "for, before;" German für "for;" Danish for "for," før "before;" Gothic faur "for," faura "before"), from PIE root *per- "forward," hence "in front of, before," etc.

Barâye "because of," related to Pers. cerâ "for what reason, why?," irâ "for this reason, therefore," zirâ "because, on account of;" also rây "opinion, consult," Mid.Pers. râd, rây "because of, for the sake of, on behalf of;" O.Pers. rā "reason, cause," in rādiy "for this reason," → reason.

Increased reddening and monochromaticity of light as the path length in the air increases.

After the Scottish physicist James David Forbes (1809-1868); → effect.

1) General: Not allowed; prohibited.
2) Physics: Involving a change in → quantum numbers that is not permitted by the → selection rules, → forbidden transition.

Past participle of forbid, from O.E. forbeodan, from for- "against" + beodan "to command" (O.E. biddan"to beg, ask, demand;" cf. Ger. bitten "to ask"); cf. Du. verbieden, O.H.G. farbiotan, Ger. verbieten.

Bažkam in classical Persian dictionaries "a keeping back, a preventing," from Av. paitigam- "to prevent," from paiti- "opposite, against, back, in return" (O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Mod.Pers. variants pâd- (→ anti-); cf. Skt. práti "opposite, against, again, back, in return, toward;" Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti) + gam- "to come; to go," jamaiti "goes;" O.Pers. gam- "to come; to go;" Mod./Mid.Pers. gâm "step, pace," âmadan "to come" (cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").

In → solid state physics, a range of → energy levels which is not attained by any electrons in a → crystal. In the energy level diagram forbidden bands appear as gaps between → allowed bands.

→ forbidden; → band .

A → forbidden line in → emission.

→ forbidden; → emission; → line.

A spectral line emitted by atoms undergoing energy transitions not normally allowed by the → selection rules of → quantum mechanics. Forbidden emission lines form in low-density interstellar gas and are collisionally excited. They are designated by enclosing in brackets, e.g. [O III] and [N II], O and N representing oxygen and nitrogen atoms respectively.

→ forbidden; → line.

A transition between two quantum mechanical → states that → violates the quantum mechanical → selection rules.

→ forbidden; → transition.

A decrease in the Galactic cosmic flux around sunspot maximum as a consequence of Solar flare activity. When sunspots explode, they often hurl massive clouds of hot gas away from the Sun, a phenomenon called → coronal mass ejections (CME). The CMEs contain not only gas but also magnetic fields. So when a CME sweeps past Earth, it also sweeps away many of the electrically-charged cosmic rays.

After Scott E. Forbush, American physicist who studied cosmic rays in the 1930s and 40s; → effect; decrease, from O.Fr. stem of descreistre, from L. decrescere, from → de- "away from" + crescere "to grow."

Kâheš, verbal noun of kâstan, kâhidan "to decrease," from Mid.Pers. kâhitan, kâstan, kâhênitan "to decrease, diminish, lessen;" Av. kasu- "small, little" (Mod.Pers. keh), Proto-Iranian *kas- "to be small, diminish, lessen."

1) The cause of a change in motion or shape of a body.
2) A → vector quantity defined by → Newton's second law as the rate of change of → momentum or, equivalently, as the product of → mass and → acceleration. A force is completely specified by giving its magnitude, direction, and point of application. In mechanics, force represents the quantitative measure of the mechanical interaction of material bodies.

From O.Fr. force, from L.L. fortia, from neut. pl. of L. fortis "strong," from forctus, from PIE base *bhergh- "high" (cf. Av. barəz- "high, mount," barezan- "height;" O.Pers. baršan- "height;" Mod.Pers. borz in (the mountain chain) Alborz, and borz "height, magnitude," bâlâ "up, above, high, elevated, height," Lori dialect berg "hill, mountain;" Skt. bhrant- "high;" O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg).

Niru, from Mid.Pers. nêrok, Av. nairya- "manly, male" (cf. Skt. nárya-), from nar- "man, male" (Mid./Mod.Pers. nar- "male," Skt. nár- "male").

Same as → field of force.

→ force; → field.

One of the three quantities (k, α, and δ) which are used in the → radiation-driven wind theory to express the radiation pressure due to spectral lines. These coefficients parametrize the radiation acceleration as: g_rad≅ k(dv/dr)^αg_e, where g_e = σ_eL/4πcR_*² is the radiative acceleration by electron scattering. The parameter k is dependent on the number of lines that produce the radiation pressure. The parameter α depends on the optical depth of the driving lines and varies between 0 (optically thin) and 1 (optically thick). The parameter δ describes the dependence of k on the density with k ≅ ρ^δ. The velocity law of radiation-driven winds depends on α and δ, but not on k. The → mass loss rate depends on k, α, and δ (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269 and references therein).

→ force; → multiplier; → parameter.

Any set of forces acting on a → rigid body.

→ force; → system.

The condition in a plasma when the → Lorentz force is zero, that is when the electric current flows along the magnetic field. Force-free magnetic fields are encountered in astrophysical plasmas with negligible gas pressure. The solar corona is the best available example of such fields in action in a plasma.

→ force; → free; → magnetic; → field.

1) Physics: Caused by an external force. → forced oscillation.
2) General: Subjected to force, compulsory.

Adjective from → force.

Adjective from zur, → strength.

A fluid flow generated when external forces cause the fluid to flow, for example when a flow is caused by a pump. It contrasts with → free flow.

→ forced; → flow.