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

The annual apparent motion of the → Sun in the sky with respect to → fixed stars along the path called → ecliptic. The apparent annual motion is due to the → Earth's → revolution about the Sun. In the course of this motion, the Sun appears to shifts about 1° eastward per day.

→ annual; → motion.

Generally, the variation of a quantity over a year. In particular the yearly change in the right ascension or declination of a star, produced by the combined effects of the precession of the equinoxes and the proper motion of the star.

→ annual; → variation.

The phenomenon whereby the → refractive index of light in a medium changes rapidly with wavelength in the vicinity of an → absorption band. Hence the → dispersion curve of the substance shows marked deviations from → Cauchy's equation, in contrast with the behavior of → normal dispersion. On the shorter λ side of the absorption band the refractive index falls off more rapidly than required by Cauchy's equation representing values of n for visible light. On the long λ side of the absorption band the index is very high, decreasing at first rapidly and then more slowly as one goes beyond the absorption band.

→ anomalous; → dispersion.

Statistics: The correlation coefficient of two random variables X and Y is in general defined as the ratio of the Cov(X,Y) to the two standard deviations of X and Y. It varies between 1 and -1 corresponding to complete correlation or anticorrelation.

Anticorrelation, from → anti- + → correlation.

Pâdhambâzâneš, from pâd-, → anti-, + hambâzâneš, → correlation.

A mathematical expression, derived from the → Clausius-Clapeyron equation, of the relation between the vapor pressure and the temperature of pure substances. It shows that the logarithm of vapor pressure is linearly dependent on the reciprocal of → absolute temperature.

Named after Louis Charles Antoine (1825-?), a French marine engineer, who derived the equation; → equation.

The point in the orbit of a planet, or other object in the solar system, which is furthest from the Sun.

Aphelion, from L. aphelium, from Gk. → apo- + helios "sun," cognate with L. sol, Skt. surya, Av. hvar-, Mod.Pers. xor, hur, O.H.G. sunna, Ger. Sonne, E. sun; PIE *sawel- "sun".

Apâhur, from Pers. prefix apâ, → apo-, + hur "sun."

The distance between the → Sun and an → object in orbit around it when they are at their farthest approach.

→ perihelion; → distance.

The point in a lunar orbit that is farthest from the center of the Lune. Also apolune.

Apocynthion, from → apo- "away from, off" + cynthion, from Gk. Cynthia "goddess of the Moon."

Apâmah, apâmâh, from apâ, → apo-, + mah, mâh, → Moon.

1) Generally, any process suppressing the secondary maxima of a diffraction pattern, such as the faint rings around the Airy disk of an optical image. This allows the telescope to resolve finer details.
2) Over a telescope aperture, the use of a screen that progressively cuts down, from the center to the edge of the aperture, the amount of light transmitted, in order to reduce diffraction.
3) A mathematical treatment carried out on data received from an interferometer before the Fourier transformation is calculated to obtain the spectrum.

Apodization from v. apodize, → a- "negation prefix" + pod from Gk. podos "foot" (compare with Pers. pâ, see below) + -tion "noun forming suffix;" literally "removing feet," i.e. suppressing the secondary maxima at the side of the Airy spot.

Pâzodâyi "removing feet," from pâ "foot," Mid.Pers. pâd, pây , Av. pad-, Skt. pat, Gk. pos, gen. podos, L. pes, gen. pedis, PIE *pod-/*ped-. Zodâyi, n. from zodudan "to polish, clean," Mid.Pers. uzdâtan, Av. uzdâ-, from uz-, → ex-, + dâ- "make, create."

1) The position on the celestial sphere at which a heavenly body would be seen from the Earth at a particular time.
2) A position given by the coordinates calculated for a star, if it were seen from the Earth's centre, relative to the → real equator and the → real equinox, at a certain date. It includes the displacements from one heliocentric direction, given in a stellar catalogue, due to → precession, → nutation, → aberration, → proper motions, → annual parallax, and light gravitational deviation (M.S.: SDE).

→ apparent; → position.

A period during which a → planet, → asteroid, or → comet is observable, generally between two successive → conjunctions of the body with the Sun.

M.E. apparicioun, from O.Fr. apparition, from L.L. appritionem "an appearance," from L. apparitus, p.p. of apparere "to appear."

Padidâri, n. from → padidâr + -i; padidâreš, verbal n. from *padidâridan.

In psychology of education, the fundamental process in acquiring knowledge, and the part played by existing knowledge.

From Fr. aperception, from N.L. apperceptionem, from ap- variant of → ad- before p + → perception.

From prefix bar- "on, upon, up" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + âgerteš, → perception.

1) General: The act of applying to a particular purpose or use.
2) Computers: A program that performs a specific function for the user, as contrasted with an environment or operating system. Some examples are Microsoft Windows, Microsoft Word, and Adobe Photoshop. The word "application" is used because each program has a specific application for the user.

Verbal noun of → apply.

A software with a specific function, such as a word processor or game. Contrast with operating system software.

→ application; → software.

1) Anxiety or fear that something bad or unpleasant will happen.
2) Understanding; grasp.
3) The action of arresting someone (Oxford Dictionary, lexico.com).

Verbal noun of → apprehend.

1) General: A guess or estimate; nearness in space, position, degree.
2) Math., Physics: Result that is not quite exact, but is within the limits of accuracy required for a given purpose.

Approximation, verbal noun of → approximate.

Nazdineš, verbal noun of nazdinidan, → approximate.

→ Rotation of the → line of apsides in the plane of the orbit in the same direction as the → revolution of the → secondary body. The major axis of the Earth's orbit rotates by 11.6 arcseconds per year.

→ apsidal; → motion.

→ advance of perihelion, → relativistic precession.

→ apsidal; → precession.

The difference in → right ascension between the → Sun and the → Moon, measured in degrees.

→ arc; → separation.

The → angular  → difference in → altitude between the → Sun and the → Moon.

→ arc; → vision.