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

A star whose variation in apparent brightness is not due to changes in the star itself but to some external cause, such as eclipsing by a companion.

→ extrinsic; → variable; → star.

The organ of vision that detects light.

O.E. ege (Mercian), eage (W. Saxon), from P.Gmc. *augon, from PIE *ok^w- "to see;" cf. Av. aši- "(both) eyes;" Skt. áksi- "eye;" Gk. osse "(both) eyes;" Goth. augo; O.C.S. oko; Lith. akis; L. oculus; Arm. ac-kh "eye."

Cašm, from Mid.Pers. cašm, Av. cašman- "eye," ākas- "to look," from prefix ā- + Proto-Iranian *kas- "to look, appear," cf. Skt. cáksus- "seeing."

The distance between the eyepiece of a telescope and the location of the exit pupil. This is where the observer's eye should be positioned to see the entire field of view of the eyepiece. Also termed eye distance.

→ eye; relief, from M.E. relef, from O.Fr. relief "assistance," from relever "to raise," from L. relevare "to raise, alleviate," from re- intensive prefix, + levare "to lift up, lighten."

Cašm nehâd "eye position," from cašm, → eye, + nehâd "position, placing, posture," contracted form of nehâdan "to place, put;" Mid.Pers. nihâtan; Av. ni- "down; into," → ni-, + dā- "to put; to establish; to give," dadāiti "he gives;" cf. Skt. dadāti "he gives;" Gk. didomi "I give;" L. do "I give;" PIE base *do- "to give."

The necessary precautions that must be taken in order to avoid damaging the eyes when watching a → solar eclipse. The only time that the Sun can be viewed safely with the naked eye is during a → total eclipse, when the Moon completely covers the disk of the Sun. It is never safe to look at a → partial eclipse or → annular eclipse, or the partial phases of a total solar eclipse, without the proper equipment and techniques. Even when 99% of the Sun's surface (the → photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause permanent retinal damage, especially when viewed through binoculars or other optical aids (F. Espenak, NASA).

→ eye; safety, M.E. sauvete, from O.Fr. salvetet, from M.L. salvitatem "safety," from L. salvus, cognate with Pers. har "all, each, every," → holo-.

Gazand "damage, injury," Mid.Pers. wizend, ultimately from *ui-jan-, from *ui- "apart, away from," → expand, + *jan- "to beat, strike," cf. Pers. zan-, zadan "to beat, strike," → beat; cašm, → eye
Zilegi, → security.

A device consisting of a pair of glass or plastic lenses worn in a frame in front of the eyes to help correct imperfect vision or protect the eyes from light, dust, and the like. Also called glasses, spectacles.

→ eye; → glass.

Eynak, probably related to âyené "mirror," âbginé "glass" (Mid.Pers. êwênag "mirror," from *âdênak, from Proto-Iranian *ādayanaka-, from prefix ā- + the root of Av. dā(y)- "to see," didāti "sees" (cf. Mod.Pers. didan "to see," Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen") + suffix -ak). Other obsolete Pers. equivalents for eyeglasses are cešm-e farangi "Frank/European eye" and âyene-ye farangi "Frank/European glass." And it seems that the oldest mention of eyeglasses in Pers. is by the poet Jâmi (1414-1492), who calls it farangi šišé "Frank/European glass." These paradigms support the relation between eynak and âyené. As for the more recent term sam'ak "hearing aid," which is invoked to relate eynak to eyn (Ar. 'ayn "eye"), it may have been coined on the model of eynak supposing that eyn means "eye."

A → lens system, also known as an → ocular, used to → magnify the → image formed by the → objective of a → telescope.

→ eye; → piece.

Cašmi "ocular," adj. of cašm→ eye + -i adj. suffix.

The exterior part of the → solar corona, illuminated by solar light scattered or reflected by dust particles. The same phenomenon also produces the → zodiacal light, much farther away from the Sun. The dust particles are at most several microns in size and make up a disk stretching over almost 1 solar radius (700,000 km) from the Sun's surface. Unlike electrons, which are responsible for the → K corona, the dust particles move relatively slowly. Thus, the light scattered by them has the same spectrum as the → photosphere and shows the → Fraunhofer lines. The F corona is the most luminous part of the corona at 1.5 solar radii from the Sun's surface (M.S.: SDE).

F referring to the Fraunhofer lines; → corona.

Waves that propagate only on the stellar surface. See also: → oscillation mode; → g mode; → p mode.

f referring to → fundamental; → mode.

The → Saturn's ring, with a width of 30-500 km, lying just outside of the → A ring, at 140,210 km from the center of Saturn.

→ ring.

An extension of Einstein's → general relativity derived from relaxing the hypothesis that the → Hilbert-Einstein action for the → gravitational field is strictly linear. This was done by replacing the → Ricci scalar, R, with a non-linear function of R:
S = (1/2κ)∫d⁴x (-g)^1/2f(R) + S^m,
where κ ≡ 8πG and S^m is the matter part of the action. The case of f(R) = R represents the simplest type of f(R) gravity theories. The discovery of → dark energy in 1998 stimulated the idea that → cosmic acceleration today may originate from some modification of gravity to general relativity. Dark energy models based on f(R) theories have been extensively studied as the simplest modified gravity scenario to realize the late-time acceleration. There are three versions of f(R) modified gravity: metric (or second order) formalism, Palatini (or first order) formalism, and metric-affine gravity.

f(R), function of the → Ricci scalar; → gravity.

Same as → focal ratio.

f, from → focal; → number.

A star whose spectrum is characterized by strong → absorption lines of ionized → calcium, Ca II (→ H and K lines), which become much stronger than the hydrogen lines of the → Balmer series. A multitude of fainter metallic lines are also present. Ca II lines strengthen to later types. → Main sequence F stars, of which → Procyon is an example, have a → surface temperature of 6,000 to 7,400°C and a mass of 1.1 to 1.4 → solar masses (Habets & Heintze, 1981, AASS 46, 193).

B, letter of alphabet used in the → → Harvard classification; → type; → star.

An empirical power-law correlation between the luminosity (L) and the velocity dispersion of stars (σ) in the center of a elliptical galaxies. The original relation can be expressed mathematically as: L ∝ σ^γ, where the index γ is observed to be approximately equal to 4, but depends on the range of galaxy luminosities that is fitted. → Tully-Fisher relation.

After the astronomers Sandra M. Faber and Robert Earl Jackson, who first noted this relation in 1976 (ApJ 204, 668); → relation.

1) A short tale to teach a moral lesson, often with animals or inanimate objects as characters.
2) A story not founded on fact.
3) A story about supernatural or extraordinary persons or incidents; legend (Dictionary.com).

M.E. able, fabel, fabul, from O.Fr. fable "story, fable, tale; drama, play, fiction; lie, falsehood," from L. fabula "story, story with a lesson, tale, narrative, account; the common talk, news," literally "that which is told," from fari "speak, tell," from PIE root *bha- "speak."

Afsâné, from Proto-Ir. *abi-sanhana-, from *sanh- "to declare, explain;" cf. O.Pers. θaⁿh- "to declare, say;" Av. səngh- "to declare;" → speech.

A type of interferometer wherein the beam of light undergoes multiple reflections between two closely spaced partially silvered surfaces. Part of the light is transmitted each time the light reaches the second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like the multiple slits of a diffraction grating increase its resolution.

The design was conceived by French physicists Charles Fabry (1867-1945) and Alfred Pérot (1863-1925) in the late nineteenth century; → interferometer.

1) To tell invented stories; create fables or stories filled with fantasy.
2) To relate an event as a fable.

From L. fabulatus perfect passive participle of fabulor, from fabula, → fable.

Afsâne-bâftan "to forge fables, stories," from afsâné, → fable, + bâftan "to weave, twist, plait," → texture.

1) To tell invented stories; create fables or stories filled with fantasy.
2) To relate an event as a fable.

→ fabulate; → -tion.

1) Almost impossible to believe; incredible.
2) Exceptionally good or unusual; marvelous; superb.

→ fable; → -ous.

1) The front part of the head, from the forehead to the chin.
2) A plane surface of a geometric solid. The front of something having more than two sides. → interface.

M.E., from O.Fr. face, from L. facies "appearance, form; visage, countenance."

Dim "face," from Av. daēman- "eye," from dā(y)- "to see," didāti "sees" (cf. Mod.Pers. didan "to see," Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").
Ru(y), variant rox "face, surface; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height").

An angle formed by any two adjacent edges of a → polyhedron, in contrast to a → dihedral angle.

→ face; → angle.