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

1) The action or result of the verb → refract.
2) Participial adjective of → refract.

From → refract + → -ing.

A prism that is used as a dispersing element in a spectrograph.

→ refracting; → prism.

A telescope in which an image is formed by the refraction of light through a lens or lens system.

→ refracting; → telescope.

A method of dating that can only tell us whether an event or object is older or younger than another event or object. In geology, different layers of rock are compared to determine an ordered sequence of events in geologic history. In contrast to → absolute dating, relative dating cannot give the actual age of a rock. See also → stratigraphy.

→ relative; → dating.

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."

Capable of or having rotation.

From → rotate + → -ing.

A black hole that possesses angular momentum, as first postulated by Roy C. Kerr in 1963. Opposite of a stationary black hole. → ergosphere.

→ rotating; → black hole.

A star that has a non-zero → angular velocity. In a rotating star, the → centrifugal forces reduce the → effective gravity according to the latitude and also introduce deviations from sphericity. In a rotating star, the equations of stellar structure need to be modified. The usual spherical coordinates must be replaced by new coordinates characterizing the → equipotentials. See also → von Zeipel theorem.

→ rotating; → star.

A → diffraction grating with a series of grooves that have been ruled on a reflective surface with a diamond tool mounted on a ruling machine. Ruled gratings may have triangular or trapezoidal groove profiles, whereas → holographic gratings usually have sinusoidal groove profiles.

Ruled, → rule; → grating.

Turi, → grating; šiyârdâr "having grooves," from šiyâr, → groove, + -dâr "having, possessor," → property.

A technique that uses → spectral energy distribution results from models to reproduce observational data.

→ spectral energy distribution; → fitting.

The characteristic of a system of masses, such as a star, kept together by mutual gravity.

→ self; → gravitate.

1) The act of setting; the appearance of a → celestial body below the → horizon. Opposite of → rising.
2) A change in a software program or hardware device that adjusts it to the user's preference. For example, date and time setting, language setting, display setting, font setting, etc.

→ set; → -ing.

Two graduated disks attached to the right ascension and declination axis of an equatorial mount used in amateur astronomy that help an observer find astronomical objects in the sky by their equatorial coordinates.

M.E.; O.E. settan "cause to sit, put in some place, fix firmly" (cf. O.N. setja, O.Fris. setta, Du. zetten, Ger. setzen); → circle.

Dâyeré, → circle; âmâj-giri "taking aim," from âmâj "aim, target," → point + giri "taking" (vebal noun of gereftan "to take, seize, hold;" Mid.Pers. griftan, gir- "to take, hold, restrain;" O.Pers./Av. 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 *ghrebh- "to seize").

Colloquial name for → meteor.

Shooting, from shoot (v.); M.E. shoten; O.E. sceotan "to shoot" (cf. O.N. skjota, Du. schieten, Ger. schießen), from PIE base *skeud- "to shoot, to chase, to throw;" → star.

Šahâb, → meteor.

Statistics: A procedure that is used to decide whether to accept or reject the → null hypothesis or to determine whether observed samples differ significantly from expected results. Also called → test of significance and → rule of decision.

→ significance; → test.

A member of a class of → B stars that are situated along the → main sequence with → spectral types ranging from B2 to B9 and masses from 3 to 7 → solar masses. In the → H-R diagram the SPB group lies below → beta Cephei variables, which are more massive. SPBs show light and line-profile variations that are multi-periodic with periods of the order of days. This variability is understood in terms of non-radial → stellar pulsations, and their → oscillation modes are high-order → g modes. Theoretical models attribute the pulsational nature of SPBs to the → kappa mechanism, acting in the metal → opacity bump at 2 x 10⁵ K. Their g-mode pulsations penetrate deep into the stellar interior, making these objects very promising for → asteroseismology. Several oscillation modes are excited simultaneously, resulting in periodicities on time scales of the order of months or even years. The prototype of this group is 53 Per. First introduced as a distinct class by Waelkens (1991, A&A 246, 453).

→ slow; → pulsating; → B star.

The act or instance of being split or causing something to split. → splitting of energy level.

Verbal noun of → split.

The splitting of a single atomic level into a group of closely spaced levels when the substance producing the single line is subjected to a uniform magnetic field. → Zeeman effect; → Stark effect.

→ spliting; → energy level.

A method of making decision between rejecting or not rejecting a → null hypothesis on the basis of a set of observations.

→ statistical; → hypothesis; → test.

A mechanism that could be responsible for global → spiral structure in galaxies either by itself or in conjunction with spiral → density waves. In this mechanism, star formation is caused by → supernova-induced → shocks which compress the → interstellar medium. The → massive stars thus formed may, when they explode, induce further → star formation. If conditions are right, the process becomes self-propagating, resulting in agglomerations of young stars and hot gas which are stretched into spiral shaped features by → differential rotation. Merging of small agglomerations into larger ones may then produce large-scale spiral structure over the entire galaxy. The SSPSF model, first suggested by Mueller & Arnett (1976) was developed by Gerola & Seiden (1978). While the → density wave theory postulates that spiral structure is due to a global property of the galaxy, the SSPSF model examines the alternative viewpoint, namely that spiral structure may be induced by more local processes. The two mechanisms are not necessarily mutually exclusive, but they involve very different approaches to the modeling of galaxy evolution. The SSPSF gives a better fit than the density wave theory to the patchy spiral arms found in many spiral galaxies. However, it cannot explain → galactic bars.

→ stochastic; → self; → propagate; → star; → formation.