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

The distance between the point of application of a → force and the → axis around which the object could → rotate.

→ lever; → arm.

One of the → spiral arms of the → Milky Way Galaxy which contains our → solar system. Same as → Orion Arm.

→ local; → arm.

Moderately warm; tepid.

M.E. lukewarme "tepid," from luke "tepid," of unknown origin, + → warm.

Velarm "lukewarm, tepid," of unknown origin.

A relatively dense collection of meteoroids at certain spots along some → meteoroid streams.

→ meteoroid; → swarm.

A minor → spiral arm of the → Milky Way Galaxy close to which the → Sun is located. It is some 3,500 → light-years across and approximately 10,000 light-years in length. The solar system lies close to the inner rim of this spiral arm, about halfway along its length. Its name derives from the fact that the stars closest to the Sun which actually lie within the arm are in the constellation → Orion. Its other designations are → Local Arm, → Local Spur, → Orion Bridge, → Orion Spur, and → Orion-Cygnus Arm.

→ Orion; → arm.

Same as → Orion Arm.

→ Orion; → Cygnus; → arm.

One of the spiral arms of the Galaxy. It is about 5000 light-years farther from the center than the local Orion Arm, in which the Sun lies.

→ Persus; → arm.

One of the → spiral arms of the Milky Way Galaxy. It lies between the Sun and the the → Scutum-Crux arm. Also known as the Sagittarius-Carina Arm.

→ Sagittarius; → arm.

A spiral arm of our Galaxy located between the Sagittarius Arm and the Norma Arm, though it is rather less prominent than either of these two better defined spiral arms. It originates relatively close to the Sun's present position in the Galaxy, and follows a sweeping arc of about 80,000 light years to the opposite side of the Galactic disk.

→ Scutum; → Crux; → arm.

The motion of a body subjected to a restraining force which is directly proportional to the displacement from a fixed point in the line of motion. The equation of simple harmonic motion is given by x = A sin(ωt + θ₀), where x is the body's displacement from equilibrium position, A is the → amplitude, or the magnitude of harmonic oscillations, ω is the → angular frequency, t is the time elapsed, and θ₀ is the → initial phase angle.

→ simple; → harmonic; → motion.

An oscillator whose force is proportional to its extension, according to → Hooke's law. The way the oscillator moves is called → simple harmonic motion.

→ simple; → harmonic; → oscillator.

A solution of some mathematical equations when → spherical polar coordinates are used in investigating physical problems in three dimensions. For example, solutions of → Laplace's equation treated in spherical polar coordinates. Spherical harmonics are ubiquitous in atomic and molecular physics and appear in quantum mechanics as → eigenfunctions of → orbital angular momentum. They are also important in the representation of the gravitational and magnetic fields of planetary bodies, the characterization of the → cosmic microwave background anisotropy, the description of electrical potentials due to charge distributions, and in certain types of fluid motion.

The term spherical harmonics was first used by William Thomson (Lord Kelvin) and Peter Guthrie Tait in their 1867 Treatise on Natural Philosophy; → spherical; → harmonic.

The region in a → spiral galaxy that contains concentrations of → gas, → dust, and → massive stars. Spiral arms are created by → density waves. See also → density wave theory.

→ spiral; → arm.

A galaxy with prominent stellar → spiral arms and little star formation between stellar arms, such as M51.

→ strong; → arm; → spiral; → galaxy.

A great number of things especially in motion. → meteorite swarm.

ME; OE swearm; cf. O.S., M.L.G. swarm, Swed. svärm, M.Du. swerm, O.H.G. swarm, Ger. Schwarm "swarm;" O.N. svarmr "tumult."

Qang in Lârestâni "swarm of bees, flies, or the like," Lori qem (qem zaye) "swarm of bees, ants, and the like."

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

→ upper; → arm.

Bâzu "arm," from Mid.Pers. bâzûk "arm;" Av. bāzu- "arm;" Mod.Pers. bâhu "stick, staff; 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").

Moderately hot.

M.E.; O.E. wearm (cf. O.S., O.Fris., M.Du., O.H.G., Ger. warm, O.N. varmr, Goth. warmjan "to warm"); cognate with Pers. garm, as below.

Garm "warm;" Mid.Pers. garm "warm;" O.Pers. garma-pada "name of the fourth month" (June-July); Av. garəma- "warm; heat;" cf. Skt. gharmá "heat;" Gk. therme, thermos; L. formus "warm;" E. warm, as above; PIE base *ghworm-/*ghwerm- "warm."

A cloud of ionized gas within → active galactic nuclei (AGN) that causes absorption at → soft X-ray wavelengths. Warm absorbers were first suggested by Halpern (1984) to explain Einstein data of the quasar MR 2251-178. They are dubbed "warm" absorbers as they imply gas at temperatures of 10⁴-10⁵ K; the gas is → photoionized, not collisionally ionized. High resolution observations of warm absorbers have shown that they are outfowing. See also → cold absorber (Ceri Ellen Ashton, 2005, A Study of Warm Absorbers in Active Galactic Nuclei, Thesis, Mullard Space Science Laboratory Department of Space and Climate Physics University College London ).

→ warm; → absorber.

Meteo.: A leading edge that advances in a mass of air and replaces cooler air by warm air.

→ warm; → front.

A component of the → interstellar medium consisting of an extremely tenuous (density 0.1 to 10 cm^-3) and relatively warm gas (temperature about 8,000 K) filling the space between denser neutral and ionized gas. Hydrogen is partly ionized, partly atomic and observed by the → 21-centimeter line in emission.

→ warm; → intercloud medium.