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

1) Each of the upper limbs of the human body, especially the part between the → shoulder and the → wrist.
2) The upper limb from the shoulder to the → elbow.
3) A slender part of a structure projecting from a main part, such as a → spiral arm. → Orion Arm; → Perseus Arm; → Scutum-Crux Arm.

M.E. arm, from O.E. earm "arm," from P.Gmc. *armaz (cf. M.Du., Ger. Arm, O.N. armr, O.Fris. erm), from PIE base *ar- "to fit, join;" cf. Mod.Pers. arm, as below.

1) Ârm (Dehxodâ, Steingass) "arm, from the elbow to the shoulder;" Av. arma-, arəmo- "arm;" cf. Ossetic ärm "hand;" Armenian armuku "elbow;" Skt. irma- "arm;" Gk. arthron "a joint;" L. armus "shoulder;" cognate with E. arm, as above.
2) Bâzu, → upper arm.

An ancient instrument, used since ancient times until the Middle ages and later, to determine positions of celestial bodies. It consisted of an assemblage of rings, all circles of the same sphere, designed to represent the positions of the important circles of the celestial sphere.

L. armillarius, from armilla "arm ring, bracelet," from armus "arm" + → sphere.

Zâtolhelaq from Ar. "multi-ringed," from zât "holder, keeper" + helaq "rings," from halqah "ring."

1) An agreement between opposing armies to stop fighting for a particular time, especially in order to discuss possible peace; truce
2) A formal agreement, especially between nations, to end combat.

From Fr. armistice, from L. arma "arms" + -stitium, from sistere "to cause to stand," → solstice.

Nâjangân, literally "state of no war," from nâ- "no, not," → un-, + jang, → war, + -ân suffix of time and place.

A sort of → greenhouse effect in → stellar atmospheres where the deeper layers heat up due to overlying → opacity. The presence of numerous → bound-bound opacities of → metals amplifies the → scattering of → photons, in particular their → backscattering, forcing the → temperature to increase in order to conserve the radiation flux and the transport of energy from the interior to the outer parts of the atmosphere.

→ back; → warming; → effect.

A → spiral arm in the Milky Way galaxy seen at its best in the → constellation → Carina, but also crossing the constellations → Vela, → Crux, and → Centaurus. It may be a continuation of the → Sagittarius arm; the combined feature is called Sagittarius-Carina arm.

→ Carina; → arm.

The fourteenth of Jupiter's known satellites; 40 km in size; → retrograde orbit. It was discovered by Nicholson in 1938.

In Gk mythology, Carme was a wife of Zeus, and the mother of Britomartis, a Cretan goddess.

An area of land devoted to the raising of animals, fish, plants, etc.

M.E. ferme "lease, rented land, rent," from O.Fr., from Vulgar L. *ferma, derivative of *fermare for L. firmare "to make firm, confirm."

Keštzâr "farm, field," from kešt past stem of keštan, variants kâštan, kâridan "to cultivate, to plant;" Mid.Pers. kištan, kâridan "to sow, plant; to make furrows;" Av. kar- "to strew seed, cultivate," kāraiieiti "cultivates;" cf. Skt. kar- "to scatter, strew, pour out," + suffix -zâr denoting profusion, abundance, as in kârzâr "a field of battle; combat" šurezâr "unfertile, salty ground; nitrous earth," xoškzâr "arid land," and so forth.

The part of the arm between the → elbow and the → wrist.

From fore- a prefix meaning "before; front; superior," related to → per-; → arm.

Araš, variant ârenj "elbow;" Mid.Pers. âranj; O.Pers. arašan- "cubit;" Av. arəθnâ- "elbow;" Skt. aratni- "elbow," Iranian stem aratan-, araθn-, borrowed from Iranian into General Slavic as aršin "ell."

An increase in the average → temperature of the Earth's → atmosphere that brings about climatic changes.

→ global; → warming.

(adj.) Of, pertaining to, or noting a series of oscillations in which each oscillation has a frequency that is an integral multiple of the same basic frequency.
(n.) A wave motion, superimposed on a fundamental wave, having a frequency which is an integral multiple of the fundamental frequency. → overtone.

From L. harmonicus, from Gk. harmonikos "harmonic, musical," from harmonia "agreement, concord of sounds," related to harmos "joint," arariskein "to join together;" PIE base *ar- "to fit together."

Hamâhang, "harmonious, concordant," from ham- "together, with; same, equally, even" (Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-; Skt. sam-; also O.Pers./Av. hama- "one and the same," Skt. sama-; Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-) + âhang "melody, pitch, tune; harmony, concord," from Proto-Iranian *āhang-, from prefix ā- + *hang-, from PIE base *seng^wh- "to sing, make an incantation;" cf. O.H.G. singan; Ger. singen; Goth. siggwan; Swed. sjunga; O.E. singan "to chant, sing, tell in song;" maybe cognate with Gk. omphe "voice; oracle."

A number whose reciprocal is the → arithmetic mean of the reciprocals of a set of numbers. Denoted by H, it may be written in the discrete case for n quantities x₁, ..., x_n, as: 1/H = (1/n) Σ(1/x_i), summing from i = 1 to n. For example, the harmonic mean between 3 and 4 is 24/7 (reciprocal of 3: 1/3, reciprocal of 4: 1/4, arithmetic mean between them 7/24). The harmonic mean applies more accurately to certain situations involving rates. For example, if a car travels a certain distance at a speed speed 60 km/h and then the same distance again at a speed 40 km/h, then its average speed is the harmonic mean of 48 km/h, and its total travel time is the same as if it had traveled the whole distance at that average speed. However, if the car travels for a certain amount of time at a speed v and then the same amount of time at a speed u, then its average speed is the arithmetic mean of v and u, which in the above example is 50 km/h.

→ harmonic; → mean.

A motion that repeats itself in equal intervals of time (also called periodic motion).

→ harmonic; → motion.

Any oscillating particle in harmonic motion.

→ harmonic; → oscillator.

Math.: Any ordered set of numbers, the reciprocals of which have a constant difference between them. For example 1, ½, 1/3, ¼, ..., 1/n. Also called → harmonic sequence.

→ harmonic; progression.

→ harmonic progression.

→ harmonic; → sequence.

Overtones whose frequencies are integral multiples of the → fundamental frequency. The fundamental frequency is the first harmonic.

→ harmonic; → series.

A low-density region separating the spiral arms of a galaxy.

Interarm, from → inter- + arm "body part," from O.E. earm "arm," from P.Gmc. *armaz (cf. M.Du., Ger. arm, O.N. armr, O.Fris. erm), from PIE base *ar- "to fit, join;" Mod.Pers. arm "arm, from the elbow to the shoulder;" Av. arma-, arəmo- "arm;" Skt. irma- "arm;" Gk. arthron "a joint," L. armus "shoulder;" → region.

Andarbâzu, from andar-, → inter-, + bâzu "arm," from Mid.Pers. bâzûk "arm;" Av. bāzu- "arm;" cf. Skt. bāhu- "arm, forearm;" Gk. pechys "forearm, arm, ell;" O.H.G. buog "shoulder;" Ger. Bug "shoulder;" Du. boeg; O.E. bôg, bôh "shoulder, bough;" E. bough " a branch of a tree;" PIE *bhaghu- "arm"); nahiyé, → region. Andararm, from andar-, → inter-, + arm, as above.

The frequency of precession of a charged particle describing a circular motion in a plane perpendicular to the magnetic induction in a uniform magnetic field.

Named after Joseph Larmor (1857-1942), an Irish physicist, the first to calculate the rate at which energy is radiated by an accelerated electron, and the first to explain the splitting of spectrum lines by a magnetic field; → frequency.

The radius of the circular motion of a → charged particle moving in a → uniform magnetic field. Same as → gyroradius, → radius of gyration, → cyclotron radius. The Larmor radius (r_L) is obtained by equating the → Lorentz force with the → centripetal force: qvB = mv²/r_L, which leads to r_L = p/(ZeB), where p is → momentum, Z is → atomic number, e is the → electron charge, and B is → magnetic induction. The frequency of this circular motion is known as the → gyrofrequency.

→ Larmor frequency; → radius.

If a system of → charged particles, all having the same ratio of charge to mass (q/m), acted on by their mutual forces, and by a central force toward a common center, is subject in addition to a weak uniform magnetic field (B), its possible motions will be the same as the motions it could perform without the magnetic field, superposed upon a slow → precession of the entire system about the center of force with angular velocity ω = -(q/2mc)B.

→ Larmor frequency; → theorem.