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

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

→ weak; → emission; → line.

In a → star cluster, an → encounter that occurs at a distance and produces only very small changes in a star's velocity.

→ weak; → encounter.

All structureless bodies fall along the same → path in a → gravitational field, independent of their composition. Also known as → universality of free fall. See also: → equivalence principle, → Einstein equivalence principle.

→ weak; → equivalence; → principle.

Same as → weak interaction.

→ weak; → force.

A gravitational bending of light by structures in the Universe that distorts the images of distant galaxies. The distortion allows the distribution of → dark matter and its evolution with time to be measured, thereby probing the influence of → dark energy on the growth of structures. Weak gravitational lensing is generally difficult to identify in individual images, in contrast to → strong gravitational lensing (see, e.g., Bartelmann & Peter Schneider, 2001, Phys. Rept. 340, 291).

→ weak; → gravitational; → lensing.

One of the fundamental forces of nature that accounts for some particle interaction, such as → beta decay (→ radioactivity), the decay of free → neutrons, → neutrino interactions, and so forth. It is short-ranged, dominating at distances of 10^-16 cm and occurs at a rate slower than that of the → strong interaction by a factor of about 10^-13, hence its name. Although the weak interaction also includes interactions in which no neutrinos are emitted, neutrino emission accompanies all weak interactions of interest to astrophysics. Weak interaction plays an important role in the evolution of the stars from birth to death. For example, the → proton-proton reaction is a weak interaction. Also called → weak force or → weak nuclear force.

→ weak; → interaction.

The → gravitational lensing in which the images are only weakly distorted, and do not form wide arcs or multiple image systems. This happens if the → gravitational lens mass in front of a source is not concentrated enough to form multiple images. The resulting small distortions cannot be seen on individual sources, as we do not know their unlensed, "intrinsic" shape. However, if an entire population of background sources is available, the distortions can be revealed, either statistically or by local averaging. See also → strong lensing.

→ weak; → lensing.

Same as → weak interaction.

→ weak; → nuclear; → force.

The discrepancy between the observed → mass loss rates and the predicted values for → weak-wind O-type stars.

→ weak; → wind; → problem.

A T Tauri star that lacks strong emission lines in its optical spectrum, and lacks both strong → stellar wind and → infrared excess. These objects are believed to be → pre-main sequence stars without obvious signs for disk → accretion. Weak-line T Tauri stars result from the evolution of → classical T Tauri stars.

→ weak; → line; → T Tauri star.

A → main sequence → O star with low luminosity and surprisingly weak → stellar wind compared to "classical" dwarfs. The → mass loss rates are lower than 10^-8 solar masses per year and the → modified wind momenta nearly 2 orders of magnitude smaller than that expected from wind models for typical O stars. Weak-wind O-type stars occur in both → metal-rich and → metal-poor environments. Their nature is not yet fully understood. same as → weak wind problem.

→ weak; → wind; → O-type star.

The state of the → atmosphere, mainly with regard to its effects of temperature, cloudiness, rainfall, wind, etc. upon life and human activities. As distinguished from → climate, weather consists of the short-term variations in the atmosphere.

M.E., from O.E. weder; cf. M.Du., Du. weder, O.H.G. wetar, Ger. Wetter "storm, wind, weather."

Havâb, short for havâ "weather; air" (see below) + âb→ water, from âb o havâ "weather; climate."
Havâ, from Ar., probably itself a loanword from Mid.Pers. vây "weather, air," Av. vayah-, vaya- "weather," from va- "to blow;" cf. Skt. va-, Gk. aemi- "to blow;" Av. vâta- "wind," Skt. vata-, L. ventus, Mod. Pers. bâd "wind." PIE *we- "to blow;" havâb contraction of havâ + âb "→ water," from âb o havâ "weather," literally "water and air."

Geology: The various processes, such as the actions of wind, rain, temperature changes and so forth, which mechanically and chemically cause exposed rocks to decompose.

From → weather + → -ing.

Sâyand, from sâyidan "to touch, to rub," variants sâbidan, pasâvidan; Khotanese sauy- "to rub;" Sogdian ps'w- "to touch;" ultimately Proto-Iranian *sau- "to rub."

1) A network of fine threads constructed by a spider from fluid secreted by its spinnerets, used to catch its prey.
2) A complex system of interconnected elements (OxfordDictionaries.com)

M.E., from O.E. webb "woven fabric, woven work, tapestry," from (cf. O.Sax. webbi, O.Norse vefr, Du. webbe, O.H.G. weppi, Ger. Gewebe "web"); Skt. ubhnati "he laces together," Per. baftan "to weave," as below; Gk. hyphe, hyphos "web;" PIE *webh- "to weave."

Vap, variant of Mid.Pers. waf-, wap- "to weave;" Baluchi gwapit, gwapt/gwap-, Yazdi vôpt/vôp- "to weave;" Mod.Pers. bâf-/bâftan; Av. ubdaēna- "made from woven material;" Proto-Ir. *uab/f "to weave;" cognate with web, as above.

The → SI unit of → magnetic flux. It is equal to 10⁸ → maxwells.

Named after German physicist Wilhelm Eduard Weber (1804-1891).

A physiological relationship stating that to make a sensation increase in arithmetical proportion, the stimulus must increase in geometrical progression. In acoustics, the → bel (B) unit is used to relate the intensity of sound to an intensity level corresponding to the human hearing sensation. Similarly, the division of stars into a scale of → magnitudes is based upon the Weber-Fechner law. Same as Fechner's law.

After Ernst Heinrich Weber (1795-1878), a German physician, was one of the first people to approach the study of the human response to a physical stimulus in a quantitative fashion, and Gustav Theodor Fechner (1801-1887), a German physicist who founded psycho-physics and proposed the mathematical formulation in 1860; → law.

A glass prism of very small angle used as an optical element to divert the path of a beam of light for a particular purpose. → absorbing wedge.

M.E. wegge; O.E. wecg "a wedge," cf. M.Du. wegge, Du. wig, O.H.G. weggi "wedge," Ger. Weck "wedge-shaped bread roll."

Gové "wedge;" Av. vada- "wedge," ^xvaδa- "deadly weapon;" cf. Skt. vadhá- "killer, deadly weapon," vadh- "to slay, kill;" Gk. othein "to push" (root of → osmosis).

A photometer in which an → absorbing wedge is inserted in the brighter of two beams until the flux densities of the two light sources are equal.

→ wedge; → photometer.

A division of time containing 7 successive days, which is completely independent of the month or the year. Unlike the month and the year, the week is an artificial unit of time, lacking an equivalent astronomical period.

M.E. weke; O.E. wice, cf. O.N. vika, M.Du. weke, O.H.G. wecha, Ger. Woche, akin to L. vicis "turn, change."

Hafté "week, hebdomad," from haft "seven" → hepta-.

If a function φ(x) is continuous on a closed interval [a,b], then for every ε > 0 there exists a polynomial P(x) such that |f(x) - P(x)| <ε, for every x in the interval.

After German mathematician Karl Wilhelm Theodor Weierstrass (1815-1897); → approximation; → theorem.