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

The brightest star in → Aquila (apparent visual magnitude 0.77), and the twelfth brightest star in the sky. Altair is a whitish A7 → main sequence star. It has one of the fastest known rotational speeds, 242 km/s at the equator, compared with the Sun's about 2 km/s.

Altair, from Ar. An Nasr at-Taiir "The Flying Vulture," from Nasr "vulture" + Ta'ir "flying."

Karkas-e Parandé "The Flying Vulture" coined by Biruni (around A.D. 1000), from karkas "vulture," Av. kahrkâsa- "devourer hen," from *kahrka "hen" (Mod.Pers. kark "hen," karak "quail") + *âsa "to eat" (Mod.Pers. âš "food, soup") + Parandé "flying," from paridan "to fly" (from Mid./Mod.Pers. par(r) "feather, wing," Av. parəna- "feather, wing;" cp. Skt. parna "feather," E. fern; PIE *porno- "feather").

1) A → mounting for → telescopes that permits both → vertical and → horizontal → rotation.
2) A telescope having such a mounting.
See also: → altazimuth coordinate system, → altazimuth instrument, → altazimuth mounting.

Altazimuth, from alt(itude) + → azimuth.

Farâzâ-sugân, from farâzâ, → altitude, + sugân, → azimuth.

The coordinate system in which the position of a body on the → celestial sphere is described with respect to an observer's → celestial horizon and → zenith. The coordinates of a point in this system are its → altitude on the → vertical circle, and its → azimuth westward (clockwise) along the celestial horizon from the observer's south. Same as → horizon coordinate system.

→ altazimuth; → coordinate; → system.

A telescope that moves vertically along the → altitude circle of a celestial body and horizontally along its → azimuth circle.

→ altazimuth; → instrument.

A → telescope mounting which has its two axes of movement aligned with the → horizon and the → zenith.

→ mounting; → mounting.

(v.tr.) To change or make different.
(v.intr.) To change or become different.

M.E. alteren, from O.Fr. altérer, from M.L. alterre, from L. alter "other," from PIE *al- "beyond" + comp. suffix -ter.

Degargun kardan, degargunidan, from degargun, from degar, → change, + -gun "manner, fashion," → elliptical, + kardan, -idan, → -ize.

1) The act or process of altering; the state of being altered.
2) The result of altering.

Verbal noun of → alter.

1) Happening or following in turns; succeeding each other continuously.
2a) (v.intr.) To occur in a successive manner (day alternates with night); To change back and forth from one state, action, or place to another.
2b) Electricity: To reverse direction at regular intervals in a → circuit.
3) (v.tr.) To do or execute in succession or one after another (to alternate work and rest).

From L. alternus "one after the other," p.p. of alternare "to do first one thing, then the other," from alternus "every other," from alter "the other".

1) Peyvâr from pey "step; after" (as in peyâpey "successively, repeatedly") + Pers. vâr "turn (succession), time (repetition), alternation". Compare with Skt. vâra "one's turn, appointed time, alteration, succession".
2, 3) Peyvâr šodan, peyvâr kardan, peyvâridan, verbs from peyvâr "alternate," as above.

Occuring in a successive manner. Acting or proceeding by turns. → alternating current.

Verbal adj. from → alternate; → -ing.

An → electric current that reverses direction of flow at regular intervals. The typical alternating current is → sinusoidal in shape. Alternating current has the advantage over → direct current in that its → voltage magnitude can be changed easily through a → transformer. Moreover, it is safer to transfer over the longer city distances and can provide more → power. The frequency of alternating current is 50 Hz (Europe) or 60 Hz (USA).

→ alternating; → current.

General: Successive change from one thing or state to another and back again.
The process of periodically varying a voltage from zero to a maximum, back to zero, to a minimum, and then to zero.

Alternation, noun from → alternate.

1) (n) A proposition or situation offering a choice between two or more things only one of which may be chosen.
2) (adj) Offering or expressing a choice. → alternative energy, → alternatively.

Alternative, from → alternate.

Degarine, from degar "other," variant digar, from Mid.Pers. dit, ditikar "the other, the second," O.Pers. duvitiya- "second," Av. daibitya-, bitya- "second," Skt. dvitiya- "second," PIE *duitiio- "second" + suffix -ine.

Energy from a source other than the conventional fossil fuel sources.

→ alternative; → energy.

Statistics: In → significance testing, any hypothesis which differs from the one being tested. A hypothesis alternative to the → null hypothesis is denoted by H₁.

→ alternative; → hypothesis.

In place of, or as an alternative to.

Adverb from → alternative.

A machine or device that produces alternating current.

Alternator, noun from → alternate + → -or.

An instrument which determines the altitude of an object with respect to a fixed level, such as sea level.

L. altus "high" + → -meter.

Farâzsanj, from farâz "above, over, aloft" + -sanj, → -meter; farâzyâb, from farâz + yâb "finder," from yâbidan "to find, discover, obtain."

The measurement of heights in the atmosphere (altitude) by an → altimeter.

→ altimeter; → -metry.

1) The height above sea level.
2) The angle between an object's position on the celestial sphere and the horizon.
3) Of a triangle, the perpendicular from the base to the opposite vertex.

Altitude, from L. altitudo, from altus "high".

Farâzâ, from farâz "above, up, upon," → height, + noun making suffix -a.

A circle on the celestial sphere that has equal altitude over the Earth's surface and lies parallel to the horizon. Also called almucantar, circle of altitude, parallel of altitude.

→ altitude; → circle.