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

The morphology of a galaxy which displays → spiral arms.

→ spiral; → structure.

The principle of conscious life; the vital principle in humans, animating the body or mediating between body and soul (Dictionary.com).

M.E., from L. spiritus "a breathing, breath; breath of life," related to spirare "to blow, breathe."

Minu "spirit;" Mid.Pers. mênôg "spirit;" Av. mainyu- "mind, mentality, mental force, inspiration," from mān- "to think," → mind.

Of, pertaining to, or consisting of → spirit.

→ spirit; → -al.

The quality or fact of being → spiritual.

→ spiritual; → -ity..

The observation that the abundance of → lithium (⁷Li) in metal-poor stars is constant regardless of the → effective temperature (> 5500 K) and the → metallicity ([Fe/H] < -2). The Spite plateau is currently interpreted as evidence that the Li observed in → halo population stars is → primordial. Since its discovery, the Spite plateau has been subject to numerous investigations, increasing the number of stars with Li measurements and extending the sample to include ever lower metallicities. Important issues are the existence or not of a significant scatter along the plateau, and the existence or not of atomic diffusion and mixing with deeper stellar zones where Li can be burnt, producing an offset with respect to the → Big Bang → nucleosynthesis abundance. Several recent studies have shown that the Spite plateau exhibits very little, if any, dispersion. There is, however, a discrepancy between recent results and that derived from Big Bang nucleosynthesis, based on the cosmological parameters constrained by the → WMAP measurements.

Named after François and Monique Spite, French astronomers, Paris Observatory, who first discovered this relation (1982, A&A 115, 357); → plateau.

An infrared telescope launched by NASA on 25 August 2003, the last in the series of Great Observatories. It was placed into a heliocentric orbit with a period of revolution that causes it to drift away from Earth at a rate of 0.1 → astronomical unit per year. Spitzer has a 85-cm primary mirror, made of beryllium and is equipped with three cryogenically-cooled science instruments: 1) IRAC (Infrared Array Camera), which operates simultaneously on four wavelengths (3.6, 4.5, 5.8, and 8 µm); 2) IRS (Infrared Spectrograph), with four sub-modules which operate at the wavelengths 5.3-14 µm (low resolution), 10-19.5 µm (high resolution), 14-40 µm (low resolution), and 19-37 µm (high resolution); and 3) MIPS (Multiband Imaging Photometer for Spitzer), three detector arrays in the → far infrared at 24, 70, and 160 µm. So far Spitzer has obtained precious data on all sorts of astronomical objects, thus contributing to all fields of astrophysics. It has also performed two sky surveys: GLIMPS, which covers 300° of the inner Milky Way galaxy, consisting of approximately 444,000 images taken at 4 separate wavelengths with the IRAC, and MIPSGAL a similar survey covering 278° of the Galactic disk at longer wavelengths.The planned nominal mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or slightly more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009. Without liquid helium to cool the telescope, most instruments are no longer usable. However, the two shortest wavelength modules of the IRAC camera are still operable and will continue to be used in the Spitzer Warm Mission.

Named in honor of Lyman Spitzer (1914-1997), an American theoretical physicist and astronomer best known for his research in star formation and plasma physics, who first suggested (1940s) placing telescopes in orbit to escape interference from the Earth's atmosphere; → space; → telescope.

A function consisting of several segments, usually → polynomials, joined smoothly together at specific points with an explicitly stated degree of accuracy. Spline functions are used to approximate a given function on an interval.

From East Anglian dialect, maybe related to O.E. splin and to modern splint. A spline was originally a slat or a thin strip of wood. A later meaning was "a long, thin, flexible strip used as a guide for drawing arcs of curves;" → function.

→ fibula.

M.E., from M.Du. or M.L.G. splinte, splente "thin piece of iron," related to M.Du. splinte "splint," probably literally "thin piece cut off."

→ fibula.

1) A crack, tear, or fissure. The act of splitting.
2) To separate by cutting, chopping, etc.

From M.Du. splitten, from P.Gmc. *spl(e)it- (cf. Dan., Fris. splitte, O.Fris. splita, Ger. spleißen "to split").

1) Fâq "a part of something separated in two sections, such as a beard, a quill pen, etc."
2) Fâqidan verbal form.

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.

In Saturn's rings, changing structures in the radial direction. It is thought that gravitational forces alone cannot account for the spoke structure, and it has been proposed that electrostatic repulsion between ring particles may play a role.

M.E.; O.E. spaca "spoke," related to spicing "large nail," from P.Gmc. *spaikon (cf. O.S. speca, O.Fris. spake, Du. spaak, O.H.G. speicha, Ger. speiche "spoke").

Parré "a rod that extends from the hub of a wheel to support or brace the rim."

Arising from internal forces or causes; independent of external agencies; self-acting.

From L.L. spontaneus "willing, of one's free will," from L. (sua) sponte "of one's own accord, willingly," of unknown origin.

Sarxod, literally "by himself/herself," from sar "head" (soru, sorun "horn;" karnâ "a trumpet-like wind instrument," variant sornâ "a wind instrument;" Mid.Pers. sar "head," sru "horn;" Av. sarah- "head," srū- "horn, nail;" cf. Skt. śiras- "head, chief;" Gk. kara "head," karena "head, top," keras "horn;" L. cornu "horn," cerebrum "brain;" P.Gmc. *khurnaz (Ger. Horn, Du. horen; cognate with E. horn, as above, from PIE *ker- "head, horn;" O.E. horn "horn of an animal," also "wind instrument;" E. horn); PIE base *ker- "head, horn, top, summit") + xod "self" (Mid.Pers. xwad "self; indeed;" Av. hva- "self, own").

The self-ignition of a substance that produces sufficient heat within itself, by a slow oxidation process, for ignition to take place without the need for an external high-temperature source. The produced heat energy is absorbed by the substance raising its temperature slowly until the → ignition temperature is reached. Same as spontaneous ignition.

→ spontaneous; → combustion.

The emission of electromagnetic radiation from an atom or molecule that does not depend on the presence of external fields.

→ spontaneous; → emission.

A physical phenomenon whereby a symmetric system becomes permanently asymmetric. A simple example is a ball lying on top of a hill in equilibrium. The hill-ball system is symmetric about the vertical axis through the top of the hill. Moreover, there is no preferred horizontal direction to the system. However, its state is unstable, since the slightest perturbing force will cause the ball to roll down the hill in some particular direction. The system becomes permanently asymmetric because the ball will not roll uphill by itself. Symmetry breaking is found in several fields of physics, for example in → magnetism (→ ferromagnetism), → thermodynamics (→ crystallization), and → particle physics, where it constitutes the basis of → electroweak interactions. In cosmology, according to the → Big Bang model, the fundamental forces of the Universe split off from one another in a form of spontaneous symmetry braking. If a single, unified force existed with a certain symmetry just after the Big Bang, if that symmetry were somehow broken so that the unified force were fractured, then the result might be several fundamental forces. See also → grand unified theory, → theory of everything, → phase transition.

→ spontaneous; → symmetry; → break.

An → atomic transition that gives rise to a → spontaneous emission.

→ spontaneous; → transition.

A meteor occurring occasionally, and not associated with any known meteor shower.

Sporadic, from M.L. sporadicus "scattered," from Gk. sporadikos "scattered," from sporas (genitive sporados) "scattered," from spora "seed, a sowing;" related to sporos "sowing," and speirein "to sow," from PIE *sper- "to strew;" → meteor.

Šahâb, → meteor; gahgâhi "from time to time," from gah, gâh "time; place" (Mid.Pers. gâh, gâs "time;" O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come").

A reproductive body in flowerless plants corresponding to the seeds of flowering ones.

From Modern L. spora, from Gk. spora "a seed, a sowing, seed-time," related to speirein "to sow, scatter."

Hâg, variant of xâg, → egg.

A period of low → solar activity that lasted from about A.D. 1420 to 1570. It occurred before → sunspots had been studied, and was discovered by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity.

Named for the German astronomer Gustav Spörer (1822-1895); → minimum.