An Etymological Dictionary of Astronomy and Astrophysics

One of the most massive → star formation regions in the → Galaxy, situated in the constellation → Aquila at the junction point of the → Galactic bar and the → spiral arms. It lies at a distance of about 6 kpc from the Sun and covers a vast area of the → Galactic plane with l = (29° to 32°) and b = (-1° to + 1°).

W 43 is a complex of more than 20 → molecular clouds in ¹³CO emission with systemic velocities ranging from 12 km s^-1 to 110 km s^-1. The total → virial mass is estimated to be several 10⁶Msun.

Close to its center, W 43-Main is undergoing a remarkably efficient episode of → star formation and qualifies as a mini-starburst Among the 15 dense cores of W 43-Main (0.2 pc FWHM size and 5 × 10⁵ cm^-3 density), three extremely massive, → dense cores are potentially forming → massive stars: W 43-MM1 (M = 3600 Msun), W 43-MM2 (M = 1600 Msun), and W 43-MM3 (M = 1000 Msun). Adjacent to W 43-Main is a → giant H II region, illuminated by a cluster of → Wolf-Rayet and → OB stars, emitting ~ 10⁵¹ → Lyman continuum photons per second and a → far-infrared  → continuum luminosity of ~ 3.5 × 10⁶  Lsun. It is not yet clear what the impact is of this → starburst cluster on the W 43-Main cloud located 2-10 pc away. With its special characteristics, W 43 represents a type of molecular cloud complex which hosts high luminosity embedded clusters. Other well-known examples are W 49 and W 51 (e.g., Nguyen Luong et., 2013, arXiv:1306.0547).

See also: Number 43 in the following catalog: Gart Westerhout, 1958, Bull. Astron. Inst. Netherlands, 14, 215, A survey of the continuous radiation from the galactic system at a frequency of 1390 Mc/s.

A → boson particle that, along with → Z boson, mediates the → weak force in particle interactions. Two kinds of W bosons exist, the W⁺ and its antiparticle W^-. With a mass of 80.4 GeV/c², the W boson is almost 100 times as massive as the → proton.

See also: W for → weak; → boson.

A member of a class of → pulsating stars with a period of 1 to 35 days located in the → instability strip of the → H-R diagram. Also known as type II Cepheid variables, W Virginis stars are typically 1.5 mag fainter than classical Type I Cepheids and have
a mass less than that of the Sun. They also exhibit a period-luminosity relation which is distinct, but works in a similar way to the relation for Type I Cepheids. Hence W Virginis stars can also be used to measure Galactic and extragalactic distances.

See also: W, alphabetical letter; → variable star designation; → Virgo; → star.

Short for → Wolf-Rayet.

See also: → Wolf-Rayet star.

Short for → Wolf-Rayet star.

See also: → Wolf-Rayet star.

The most luminous → galaxy known. It has a → redshift of z = 4.601 and a → bolometric luminosity of 3.5 × 10¹⁴Lsun. W2246-0526 hosts a deeply buried → active galactic nucleus (AGN)/→ supermassive black hole (SMBH). Discovered using the → Wide-field Infrared Survey Explorer (WISE), W2246-0526 is classified as a → hot dust-obscured galaxy, based on its → luminosity and → dust temperature (T. Diaz-Santos et al. 2015, arXiv:1511.04079).

See also: Object designation from → Wide-field Infrared Survey Explorer (WISE).

To walk through water, snow, sand, or any other substance that impedes free motion or offers resistance to movement (Dictionary.com).

Etymology (EN): M.E. waden “to go, wade;” O.E. wadan “to go;” cf. Dan. vade, O.Fris. wada, Du. waden, Ger. waten, O.Norse vatha; akin to O.E. wæd “ford, sea,” L. vadere “to go, rush,” vadum “shoal, ford.”

Etymology (PE): Gampidan, related to Proto-Ir. *gamp-, *gamb- “to move,” cf. Dezfuli gomba, Bardesiri gopak “jump with two feet;” Sogd. (+ *â-) âγamp “walking;” (+ *uz-) Yighda žib-/žibi- “to rise, to stand,” jib- “to awake;” (+ *ham-) Wakhi gəfs-/gəfst- “to run.”

1. The track left by a moving ship.
   

2. A turbulent region appearing behind an object in a fluid which streams around the object, for example behind an aircraft in flight.

Etymology (EN): Cognate with M.L.G. wake “wake,” Nor. dialect vok, O.N. vok, voka “hole in the ice.”

Etymology (PE): Kel, from Tabari kel, kal “trail, track, footprint.”

1. To move along on foot at a moderate pace; advance by steps.
   

2a) An act or instance of walking.

2b) Physics: A moving of a particle among particles.
→ random walk; → quantum walk.

Etymology (EN): M.E. walken, from O.E. wealcan “to toss, roll;” cf. O.N. valka “to drag about,” Dan. valke “to full,” M.Du. walken “to knead, press, full,” O.H.G. walchan “to knead,” Ger. walken “to full.”

Etymology (PE): Camidan “to walk (proudly),” variant gâmidan “to walk,”
gâm “step, pace” (related to âmadan “to come,” → consequence); Mid.Pers. gâm “step, stride, pace;”
O.Pers. gam- “to come; to go;” Av. gam- “to come; to go,” jamaiti “goes;” cf. Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE stem *g^wem- “to go, come.”
Puyeš, verbal noun of puyidan “to walk, run, trot; wander,” from Mid.Pers. pôy-, pwd- “to run;” cf. Gk. speudein “to hasten;” Lith. spudinti.

1. An upright continuous structure that divides one area from another or surrounds an area.
   

   2. A wall-like, enclosing part, mass, or thing .

Etymology (EN): M.E., from O.E. w(e)all “rampart, dike, cliff,” also “defensive fortification around a city, side of a building” (O.Sax., O.Fris., M.L., M.Du. wal), from L. vallum “wall, rampart.”

Etymology (PE): Divâr “wall,” from Mid.Pers. dîvâr “wall;” related to Mid.Pers. bâr, var “enclosure, defences, fortress;” Mod.Pers. bâru “wall, rampart, fortification; fort; tower;” O.Pers. didā- “wall, stronghold, fortress;” Av. var- “castle,” from var- “to cover, conceil;” Proto-Iranian *dida-vāra-; cf. Skt. dehī- “wall;” Gk. teikhos “wall;” E. dike, ditch.

A photometric system with five wavelength ranges that does not use
filters. Instead it uses prisms and lenses (spectroscopy) to select the bands simultaneously. The wavelengths and the bandwidths are: W, 3250 and 140 Å; U, 3630 and 240 Å; L, 3840 and 230 Å; B, 4320 and 450 Å; and V, 5470 and 720 Å. The Walraven photometer was unique in design and remained literally unique as copies were never built. In addition, during its whole life the photometer was mounted permanently on the same telescope that had been built specifically for this instrument, the 91 cm Lightcollector’ reflector, which started in 1958 at the Leiden Southern Station in Broederstroom, South-Africa. After 20 years in South-Africa the telescope and photometer were moved to the European Southern Observatory La Silla observatory in Chile. The photometric observations were resumed in March 1979 and continued for another 12 years until the decommissioning of the photometer in 1991.

See also: After the inventors, the Dutch astronomer Theodore Walraven (1916-) and his wife Johanna Helena Walraven, née Terlinden (1920-89); → photometry.

Decreasing in strength, intensity, power, etc.

Etymology (EN): Waning, from wane, from M.E. wanen (v.), O.E. wanian “to lessen;” cf. O.S. wanon, O.N. vana, O.Fris. wania, M.Du. waenen, O.H.G. wanon “to wane, to grow less.”

Etymology (PE): Kâhandé “waning, decreasing;” from kâstan, kâhidan “to decrease;” Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” Av. kasu- “small, little” (Mod.Pers. keh); Proto-Iranian *kas- “to be small, diminish, lessen.”

The crescent phase of the Moon following the → last quarter which finally disappears with setting Sun.

See also: → waning; → crescent.

The oval shape of the moon a few days after the → full moon and before the → last quarter.

See also: → waning; → gibbous.

The circumstance when the phase of the Moon is decreasing from → full moon to → new moon.

See also: → waning; → moon.

A state of armed conflict between states, or between groups within states.

Etymology (EN): From M.E. werre, from O.E. werre, wyrre, from Old Northern Fr. werre, akin to O.H.G. werra “confusion, strife, quarrel,” Du. war “confusion, disarray,” O.E. wyrsa, wiersa “worse,” O.Norse verri “worse; confounded;” ultimately from PIE *wers- “to confuse, mix up.”

Etymology (PE): Jang, from Mid.Pers. jang “struggle, battle, fight.”

Moderately hot.

Etymology (EN): 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.

Etymology (PE): 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 ).

See also: → warm; → absorber.

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

See also: → 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.

See also: → warm; → intercloud medium.

The space containing a cluster of galaxies filled with a tenuous gas of temperature 10⁵ to 10⁷ K and density 10^-6 to 10^-4 cm^-3.
WHIM has been continuously shock-heated during the process of structure formation. It is so highly ionized that it can only absorb or emit far-ultraviolet
and soft X-ray photons, primarily at spectral lines of highly ionized C, O, Ne, and Fe. WHIM is thought to be the main reservoir of missing baryons.

See also: → warm; → hot; → intergalactic medium.

The process of becoming warmer; a rising temperature. → backwarming, → heating.

See also: → warm; → -ing.

The vertical twisting of a → galactic disk in its outer parts. Many → spiral galaxies, including our Milky Way, appear to have warps in the outer reaches of their stellar and gas disks. The rotating body of stars and gas that characterizes a spiral galaxy is generally flat, but the outer regions may deviate from the plane of the disk. The causes are multiple, some warps can come from spontaneous instability, some result from interactions between galaxies, and many reflect the external gas → accretion from intergalactic matter filaments.

Etymology (EN): M.E. werpen, OE weorpan “to throw;” cf. O.S. werpan, O.N. verpa “to throw,” Swed. värpa “to lay eggs,” Du. werpen, Ger. werfen “to throw; to distort.” Related to warp “threads running lengthwise in a fabric.”

Etymology (PE): Tâb “twisting, bending, waving, a curling lock,” variants tâv, tow, tew, from tâbidan, tâftan “to twist, to spin, to bend, to crook,” p.p.
tâftah “spun, silk or linen cloth,” loaned into E. as taffeta (from O.Fr. taffetas, from It. taffeta); similarly Gk. tapetion “little carpet” is probably from this Iranian origin (from which tapestry, tapis); Proto-Ir. *tâp- “to twist, to wind;” cf. L. tempus “time (span);” Lith. tempti “to stretch;” Russ. tepsti “to tighten.”

A → galactic disk that exhibits a → warp phenomenon.

See also: → warp; → disk.

1. Geology: The slight flexing or bending of the Earth’s → crust on a broad or regional scale, either upward or downward.
   

2. Of a galaxy, → warped disk, → warp.

See also: Verbal noun from → warp (v.).

A hard rough lump growing on the skin, caused by infection with certain viruses and occurring typically on the hands or feet (TheFreeDictionary.com).

Etymology (EN): M.E., from O.E. weart “wart,” cf. O.Norse varta, O.Frisian warte, Du. wrat, O.H.G. warza, Ger. Warze, Swed. varta, Russ. vered “ulcer,” perhaps ultimately from the same source as L. verruca “a steep place, swelling, wart” (Fr. verrue, Sp. verruga, Catalan berruga, It. verruca), ultimately from PIE *uer-s- “a steep place, height,” from *uer- “highland, high place, top;” cf. Gk. ouranos “sky.”

Etymology (PE): Zegil “wart,” maybe related to Pers. gereh “knot,” ultimately from prefixed (*uz-, → ex-) *graθH- “to tie (a knot).”
Veruk “wart,” variants vâruk, vâru, veri, var, oru, bâlu, bâlik, belik (also “the clitoris” in dialects), belije, bâlur, bali, maybe variants of zegil “wart,” as above, ultimately from Proto-Ir. *graθH- “to tie (a knot).”

To apply → water or other → liquid in order to cleanse.

Etymology (EN): M.E. washen; O.E. wascan, wæscan; cf. O.N. vaska, M.Du. wasscen, Du. wassen, Ger. waschen, from stem *wat-, the root of → water.

Etymology (PE): Mid.Pers. šustan, šuy- “to wash;” Av. xšaoδah- “flush of water,” xšudra- “liquid, fluid; semen;” cf. Skt. ksod- “to dissolve;” Proto-Ir. *xšaud- “to wash” (Cheung 2007).

A stellar catalog which is the world’s principal database of astrometric → double star information. It is maintained by the United States Naval Observatory. The WDS Catalog contains positions (J2000), discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions, and, when available, Durchmusterung numbers and notes for the components of 142552 systems (as of Feb 27 2018).

See also: Washington, referring to the location of the United States Naval Observatory in Northwest Washington, D.C; → double; → star; → catalog.

Unwanted or unusable items, remains, or byproducts. → nuclear waste; → radioactive waste.

Etymology (EN): M.E., from O.Fr. wast, g(u)ast, from L. vastum, neuter of vastus “waste.”

Etymology (PE): Âxâl “waste, rubbish,” of unknown origin.

The normal oxide of hydrogen with formula H₂O. Pure water’s → melting point is 0°C and its → boiling point 100 °C at sea level. Water has a → maximum density at very nearly 4°C of (by definition) 1.0000 g cm^-3. It then expands as its temperature drops to 0°C, the density being 0.9998 g cm^-3 . On freezing, it expands still further, giving ice a density of 0.9168 g cm^-3 at 0°C, whereas water has a density of 0.9998 g cm^-3 at 4 °C.

A → water molecule consists of one → oxygen (O) atom bonded to two → hydrogen (H) atoms.

The → specific heat of water, 1 calorie per gram per 1 degree C (cal/g/°C), is higher than most other substances. Therefore, water both absorbs and releases heat more slowly than land. This causes land areas to heat more rapidly and to higher temperatures and also cool more rapidly and to lower temperatures, compared to oceans. The high heat capacity of water also explains why the temperatures of land near a body of water are more moderate. The high heat capacity of water keeps its temperature within a relatively narrow range, causing nearby coastal areas to also have a narrow daily and seasonal temperature range. See also → heavy water, → ortho-water, → para-water.

Etymology (EN): Water, from O.E. wæter (cognates: Du. water; O.H.G. wazzar; Ger. Wasser; Goth. wato); cf. Gk. hydro-, combining form of hydor “water,” cognate with Skt. udá- “water;” Khotanese ūtcā “water;” Hittite uātar; L. unda “wave;”
O.C.S., Rus. voda; Lith. vanduo; from PIE base *wed- “water; wet.”

Etymology (PE): Âb “water,” variants iv, êw, âp; from
Mid.Pers. âb “water;” O.Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis);
O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook.”

An ancient form of clock, used by several civilizations, consisting of a water container with a small hole from which the water slowly dripped. Time was reckoned by the level of the water remaining in the container.

Etymology (EN): → water; → clock

Etymology (PE): Pang “a copper bason with a small hole in the bottom, for water in which it is placed to flow through, used for measuring time” used in Iran.

Water in the → solid state,
produced by freezing → liquid water; frozen water. Ice forms at or below a temperature of 0°C. Ice is less dense than liquid water because it expands during the process of freezing. This is because the molecular arrangement taken by ice leads to an increase in volume and a decrease in density. → maximum density of water

See also: → water; → ice.

An interstellar → maser phenomenon in which water (H₂O) molecules undergo the processes of → population inversion and → stimulated emission. H₂O masers are detected toward star formation regions and the envelopes of evolved stars.
The maser emission comes from regions that are typically quite small, not larger than the solar system. The main emission frequency is 22 GHz, which shows up in strong lines. There are, however, other H₂O maser transitions at 380 GHz and 183 GHz, which are much weaker than the 22 GHz line. The former transitions are sporadically detected since they are strongly absorbed in the Earth’s atmosphere, because of its high water vapor content.

See also: → water; → maser

The chemical combination of one → oxygen (O) atom bonded to two → hydrogen (H) atoms. The bonding between the oxygen atom and each hydrogen atom is known as → covalent bonds. The two hydrogen atoms are bonded to the oxygen atom at a 105° angle. This geometry of the water molecule causes it to have positively and negatively changed ends, known as → polarity. Water is referred to a polar or dipolar molecule. The large nucleus of the oxygen atom attracts the shared electrons causing this side of the water molecule to be negatively charged while the hydrogen side is positively charged. This polarity allows water to bond easily with adjacent water molecules.

See also: → water; → molecule.

Same as → ocean planet.

See also: → water; → planet.

1. Water (H₂O) in the gaseous state.
   

2. Meteo.: Atmospheric water in vapor form; one of the most important components of the → atmosphere.

See also: → water; → vapor.

A spinning column of rising humid air that occurs over a body of warm water. Waterspouts fall within the class of atmospheric phenomena known as convective vortices that includes → tornadoes, → dust devils, and → hurricanes. They can feature wind speeds over 200 kilometers per hour.

Etymology (EN): → water + spout, from
M.E. spouten akin to M.Du. spiten “to spout;” O.E. spiwan “to spew.”

Etymology (PE): Tanure-ye daryâyi, from tanuré (kešidan) “turning and raising in the air,” probably from tanidan “to turn, spin,” → tension; daryâyi, → marine.

A unit of power in the SI or MKS system of units, symbol W, equivalent to one joule per second.
1 W = 1 J s^-1 = 1 kg m² s^-3 = 1 N m s^-1 = 10⁷ erg s^-1.
Electricity: The current in amperes multiplied by the electrical potential in volts.

See also: In honor of James Watt (1736-1819) the eminent Scottish inventor and mechanical engineer.

Unit of work or energy, equal to one watt for one hour, or 3.6 x 10¹⁰ ergs., or 3600 joules. The kilowatt-hour (kWh), i.e. 1,000 watts over the period of one hour, is the usual unit or measure of electricity supply or consumption. 1 kWh = 3.6 x 10⁶ J.

See also: → watt; → hour.

A fleshy lobe or appendage hanging down from the throat or chin of certain birds, as the domestic chicken or turkey (Dictionary.com).

Etymology (EN): Of uncertain origin.

Etymology (PE): Jil (in Nâini and Baxtiyâri) “wattle.”

An instrument used for measuring the magnitude of the power in an electric circuit.

See also: → watt; → -meter.

1. General: A raised ridge-shaped formation moving across the surface of a liquid (as of the sea).
   

2. Physics: A disturbance advancing from point to point in a → medium or → space as in the → propagation of → sound or → light.
   

See also:
→ acoustic wave, → acoustic wave equation, → advanced wave, → Alfven wave, → ballistic wave, → blaze wavelength, → bow wave, → collapse of the wave function, → complex wave, → compressional wave, → cosmic microwave background anisotropy, → cosmic microwave background radiation, → decimetric wave, → density wave, → density-wave theory, → elastic wave, → electromagnetic wave, → electrostatic wave, → gravitational wave, → gravity wave, → half-wave plate, → heat wave, → incoherent wave, → Langmuir wave, → longitudinal wave, → Mach wave, → microwave, → microwave background radiation, → microwave radiation, → millimeter wave, → millimeter-wave astronomy, → modulated wave, → Moreton wave, → neutral wave, → P-wave, → periodic wave, → plane wave, → quarter-wave plate, → radio wave, → rarefaction wave, → retarded wave, → Rossby wave, → S-wave, → scalar wave, → seismic wave, → Shack-Hartmann wavefront sensor, → shear wave, → shock wave, → sine wave, → sound wave, → square wave, → standing wave, → stationary wave, → submillimeter wave, → transverse wave, → wave equation, → wave function, → wave mechanics, → wave nature, → wave numbe, → wave optics, → wave packet, → wave plate, → wave theory of light, → wave vector, → wave-particle duality, → waveband, → waveform , → waveform analysis, → wavefront, → wavefront correction, → wavefront distortion, → wavefront sensor, → wavefront tilt, → waveguide, → wavelength, → wavelet, → wavelet theory, → wave train.

Etymology (EN): M.E. waw; O.E. wagian “to move to and fro,” wafian “to wave with the hands” (cf. O.N. vafra “to hover about,” M.H.G. waben “to wave, undulate”).

Etymology (PE): Mowj, loan from Ar. mauj.

In the → Copenhagen Interpretation of → quantum mechanics,
the change undergone by the → wave function of a particle when a measurement is performed on the particle. The wave function collapses to one that has a definite value for the quantity measured. If the → position of the matter wave is measured, it collapses to a localized → pulse. If → momentum is measured, it collapses to a wave with a definite momentum. Same as → collapse of the wave function.

See also: → wave; → collapse.

The partial differential equation

∂²U / ∂²x + ∂²U / ∂²y + ∂²U / ∂²z = (1/c²) ∂²U / ∂²t
or its counterparts in one or two dimensions or in other coordinates,
the solution of which represents the propagation of displacementU as waves with velocity c.

See also: → wave; → equation.

In → quantum mechanics, the function of space and time that satisfies → Schrodinger equation.
The square of the modulus of its amplitude at any point represents the probability of finding a particle there.

See also: → wave; → function.

One of the forms of quantum mechanics, due to Louis de Broglie and extended by E. Schrödinger. It originated in the suggestion that light consists of corpuscles as well as of waves and the consequent suggestion that all elementary particles are associated with waves.

See also: → wave; → mechanics

A general term to describe → light involving the following phenomena:
→ reflection, → refraction, → interference, → diffraction, and → polarization. Compare → particle nature.

See also: → wave; → nature.

The reciprocal of → wavelength, which represents the number of waves per unit length. Wave number is often defined as k = 2π/λ. Same as → propagation number.

See also: → wave; → number

The branch of optics that analyzes the electromagnetic radiation in terms of its wave characteristics. Also called → physical optics.

See also: → wave; → optics.

A traveling → waveform consisting of the → superposition of several → waves of different → wavelengths and → phases.

Etymology (EN): → wave; packet from M.E. pak “bundle” + diminutive suffix -et; maybe from M.Fr. pacquet.

Etymology (PE): Basté “packet,” literally “bound, tied; set,” p.p. of bastan “to form, bind, tie” (Mid.Pers. bastan/vastan “to bind, shut;” Av./O.Pers. band- “to bind, fetter,” banda- “band, tie;” cf. Skt. bandh- “to bind, tie, fasten;” Ger. binden; E. bind; PIE base *bhendh- “to bind”).

An optical element that retards the phase of one plane of vibration of light relative to the plane at right angles. The two beams then recombine to form a single beam with new polarization characteristics. A typical wave plate is a birefringent crystal with a carefully chosen orientation and thickness. Also known as → retardation plate. A → half-wave plate creates a half-wave retardation. See also → quarter-wave plate.

See also: → wave; → plate.

The theory that describes light as waves that spread out from the source that generates the light. It contradicts the → corpuscular theory of light proposed by Newton (1704). The idea of the wave nature of light was first put forward by Robert Hooke (1660). The wave theory was originally stated by Huygens (1690), who showed reflection and refraction could be explained by this theory. It was supported by → Young’s experiment (1802) and established by the work of Fresnel (1814-1815). The wave theory received its most important support from Maxwell’s → electromagnetic theory. See also → Huygens-Fresnel principle.

See also: → wave; → theory; → light.

A series of successive waves spaced at regular intervals.

See also: → wave; → train.

A vector whose direction is that of propagation of a wave and whose magnitude is given by the → wave number, 2π/λ, where λ is the → wavelength, or ω/c, where ω is the → angular frequency and c is the speed of propagation.

See also: → wave; → number.

The principle admitted in → quantum mechanics that all particles have a wave-like nature and that waves have a particle aspect. The wave-particle duality is of fundamental importance in obtaining a realistic picture of the → elementary particles.

See also: → particle nature, → wave nature, → de Broglie hypothesis, → Davisson-Germer experiment.

See also: → wave; → particle; → duality.

A portion of the electromagnetic spectrum which is defined because of its characteristics or for its use.

See also: → wave; → band.

A graphical representation of the shape of a wave for a given instant in time.

See also: → wave; → form.

The resolution of a complex waveform into a sum of simple periodic waves, usually by computer means.

See also: → waveform; → analysis.

The locus of adjacent points possessing the same phase in the path of a wave motion. Its surface is uniform (spherical or plane) and normal to propagation direction in an isotropic medium. → wavefront distortion.

See also: → wave; → front.

In → adaptive optics, eliminating the effects of atmospheric turbulence on the wavefront of the object being observed. → wavefront distortion.

See also: → wavefront; → correction.

The disruption of the spherical shape of a wavefront due to atmospheric turbulence which makes the adjacent points in the wavefront out of phase.

See also: → wavefront; → distortion.

In adaptive optics, a device that analyzes the light sample coming from the wavefront and determines the error in each part of the beam. The wavefront sensor used in adaptive optics is a → Shack-Hartmann type, which works in conjunction with a deformable mirror.

See also: → wavefront; → sensor.

The average slope in both the X and Y directions of a → wavefront or phase profile across the pupil of an optical system.

See also: → wavefront; → tilt.

Any transmission medium, such as a hollow metal conductor, coaxial cable, or glass fiber, capable of confining and supporting the propagation of electromagnetic waves regardless of wavelength or mode of propagation.

Etymology (EN): → wave; guide, M.E., from O.Fr. guider “to guide, lead,” from Frankish *witan “show the way,” from P.Gmc. *wit- “to know” (cf. Ger. weisen “to show, point out,” wissen “to know;” O.E. witan “to see”). Cognate with Pers. bin- “to see” (present stem of didan “to see”); Mid.Pers. wyn-;
O.Pers. vain- “to see;” Av. vaēn- “to see;”
Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see.”

Etymology (PE): Mowjbar, from mowj, → wave, + -bar “carrier,” from bordan “to carry, lead” (Mid.Pers. burdan,
O.Pers./Av. bar- “to bear, carry,” barəθre “to bear (infinitive),” Skt. bharati “he carries,” Gk. pherein, L. fero “to carry;” PIE base *bher- “to carry”).

The distance between two successive points in the wave that are characterized by the same phase of oscillation; e.g. → de Broglie wavelength; → Compton wavelength; → blaze wavelength; → peak wavelength; → center wavelength; → central wavelength; → cutoff wavelength.

See also: → wave; → length.

A small wave; ripple.

See also: → wave + -let a diminutive suffix.

A refinement of → Fourier analysis which enables to simplify the description of a complicated function in terms of a small number of coefficients.
The formal history of wavelet theory began in the early 1980s when Jean Morlet, a French geophysicist, introduced the concept of wavelet and studied wavelet transform as a new tool for scientific signal analysis. In 1984, his collaboration with Alex Grossmann yielded a detailed mathematical study of the continuous wavelet transforms and their various applications. Although similar results had already been obtained 20-50 years earlier by several other researchers, the rediscovery of the old concepts provided a new method for decomposing functions.

See also: → wavelet; → theory.

1. A substance that is secreted by bees and is used by them for constructing the honeycomb, that is a dull yellow solid plastic when warm, and that is composed of a mixture of esters, cerotic acid, and hydrocarbons; called also beeswax.
   

2. Any of various substances resembling the wax of bees (Merriam-Webster.com).

Etymology (EN): M.E. waxen, O.E. weaxan; cognate with Du. was, Ger. Wachs.

Etymology (PE): Mum “wax; wax-candle.”

Increasing in extent, quantity, intensity, power, etc.

Etymology (EN): Waxing, from wax, from M.E. wax “to grow bigger, greater;” O.E. weaxan “to increase, grow;” cf. O.H.G. wahsan, O.N. vaxa, Du. wassen, Ger. wachsen “to grow, increase;” cognate with Mid.Pers. waxš-, waxšidan “to grow;” Av. xaxš- “to grow,” xaxša- “growth;” Skt. vaks- “to grow, become big;” Gk. auxein “to increase.”

Etymology (PE): Fazâyandé “waxing, incresing,” from fozudan, variant of afzudan “to add, increase” (Mid.Pers. abzudan “to increase, grow;” O.Pers. abijav- “to increase, add to, promote,” from abi-, aiby- “in addition to; to; against” + root jav- “press forward;” Av. gav- “to hasten, drive;” Sk. jav- “to press forward, impel quickly, excite,” javate “hastens”).

The phase of the Moon between the → new moon and the → first quarter which first appears in the evening.

See also: → waxing; → crescent.

The oval shape of the Moon a few days after the → first quarter.

See also: → waxing; → gibbous.

The circumstance when the phase of the Moon is increasing from → new moon to → full moon.

See also: → waxing; → moon.

A road, track, or path.

Etymology (EN): M.E. wei(gh)e, wai, from
O.E. weg “road, path;” cf. Du. weg, O.H.G. weg, Ger. Weg, Goth. wigs “way;” PIE base *wegh- “to move.”

Etymology (PE): Râh “way, path” (from Mid.Pers. râh, râs “way, street,” also rah, ras “chariot;” from Proto-Iranian *rāθa-; cf. Av. raθa- “chariot;” Skt. rátha- “car, chariot,” rathyā- “road;” L. rota “wheel,” rotare “to revolve, roll;” Lith. ratas “wheel;” O.H.G. rad; Ger. Rad; Du. rad;
O.Ir. roth; PIE *roto- “to run, to turn, to roll”);

A → Wolf-Rayet star whose spectrum is dominated by emission lines of ionized carbon: C III 5696 Å, C III / C IV 4650 Å, C IV 5801-12 Å. This type is divided in sub-types WC4 to WC9.
For theoretical models, a Wolf-Rayet star whose carbon abundance at surface is larger than nitrogen abundance and has the abundance ratio (C + O) / He < 1 (in number).

See also: W short for Wolf-Rayet star, C for → carbon.

A → WC Wolf-Rayet that its spectrum shows the following emission line characteristics:
strong C IV 5801-12 Å, weak or absent C II 4267 Å, and moderate O V 5572-98 Å.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics: C III 5696 Å very weaker than C IV 5801-12 Å and C III weaker than O V 5572-98 Å.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics:
C III 5696 Å very weaker than C IV 5801-12 Å and C III stronger than O V 5572-98 Å.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet with a spectrum shows the following emission line characteristics:
C III 5696 Å weaker than C IV 5801-12 Å and C III very stronger than O V 5572-98 Å.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet with a spectrum shows the following emission line characteristics:
C III 5696 Å stronger than C IV 5801-12 Å, C II 4267 Å absent, and O V 5572-98 Å weak or absent.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics: C III 569 Å stronger than C IV 5801-12 Å, C II 4267 Å present, and O V 5572-98 Å weak or absent.

See also: W, from → Wolf-Rayet; C, from → carbon; → star.

Not powerful or intense.
→ electroweak epoch, → electroweak force, → electroweak interaction, → weak anthropic principle, → weak arm spiral galaxy, → weak emission-line central star, → weak encounter, → weak equivalence principle, → weak force, → weak gravitational lensing, → weak interaction, → weak lensing, → weak nuclear force, → weak wind problem, → weak-line T Tauri star, → weak-wind O-type star.

Etymology (EN): From O.N. veikr “weak,” cognate with O.E. wac “weak, pliant, soft,” from P.Gmc. *waikwaz “yield,” *wikanan “bend” (cf. Du. week “weak, soft, tender,” O.H.G. weih “yielding, soft,” Ger. weich “soft,” from PIE base *weik- “to bend, wind”

Etymology (PE): Nezâr “weak, feeble, thin, slim; flesh without fat” (bâde-ye nezâr “a wine with minute alcohol,” soxan-e nezâr “inconsistent, weak statement”), variant zâr, Mid.Pers. nizâr (prefixed *ni- + *zâr/*zar) “weak, feeble,” Mid./Mod.Pers. zarmân “old man, deterioration,” Av. zairina- “exhausting, slackening,” zaurura- “weak through old age, decrepit,” cf. Skt. jára- “wearing out, exhaustion,” jaranā- “old, decayed,” jarimán- “weakness through old age,” Gk. geron “old man,” L. granum “grain;” PIE base *ger- “wear away.”
Tâm, → faint.
Sost, from Mid.Pers. sust “weak, lazy.”
Kamnur, from kam “little, few; deficient, wanting; scarce”
(Mid.Pers. kam “little, small, few,” O.Pers./Av. kamna- “small, few”)

• nur, → light.
  Kamzur, from ham + zur, → strength.

A version of the → anthropic principle whereby the initial conditions in the → Universe are → constrained by the fact that → intelligent life has appeared.

See also: → weak; → anthropic; → principle.

A gas-rich galaxy that has weak stellar → spiral arms with → interarm gas and star formation more important than a typical → spiral galaxy, such as NGC 4414.

See also: → weak; → arm; → spiral; → galaxy.

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).

See also: → 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.

See also: → 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.

See also: → weak; → equivalence; → principle.

Same as → weak interaction.

See also: → 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).

See also: → 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.

See also: → 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.

See also: → weak; → lensing.

Same as → weak interaction.

See also: → weak; → nuclear; → force.

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

See also: → 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.

See also: → 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.

See also: → 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.

Etymology (EN): M.E., from O.E. weder; cf. M.Du., Du. weder, O.H.G. wetar, Ger. Wetter “storm, wind, weather.”

Etymology (PE): 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.

Etymology (EN): From → weather + → -ing.

Etymology (PE): 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)

Etymology (EN): 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.”

Etymology (PE): 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.

See also: 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.

See also: 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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → 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.

Etymology (EN): 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.”

Etymology (PE): 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.

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

A test for uniform convergence of a sequence of functions. If there exists a series of numbers Σ M_i (summed from n = 1 to ∞), in which M_i≥ Σ |u_i(x)| for all x in the interval [a, b] and Σ M_i is convergent, the series u_i(x) will be uniformly convergent in that interval.

See also: → Weierstrass approximation theorem; M referring to → majorant; → test.

1. The force of attraction of the Earth on a given mass. → molecular weight; → weightlessness.
   

2. Statistics: A measure of the relative importance of an item in a statistical population. → weighted mean.
   

See also:

→ atomic weight, → counterweight, → mean molecular weight, → molecular weight, → statistical weight, → weight concentration, → weight fraction, → weight of a tensor density, → weight-fraction concentration, → weightlessness.

Etymology (EN): M.E., from O.E. gewiht, cf. O.N. vætt, O.Fris. wicht, M.Du. gewicht, Ger. Gewicht.

Etymology (PE): Vazn, loan from Ar. wazn.

of a gas included in the composition of a → gas mixture, the ratio of mass of this gas to the mass of the whole mixture. Same as → weight fraction and → weight-fraction concentration.

See also: → weight; → concentration.

Same as → weight concentration.

See also: → weight; → fraction.

A constant the value of which is characteristic for any given → tensor density.

See also: → weight; → tensor; → density.

Same as → weight concentration.

See also: → weight; → fraction; → concentration.

An mean which is obtained by combining different numbers according to the relative importance of each.

See also: → weight; → mean.

The phenomenon experienced by a body when there is no force of reaction on it. This happens when the body is in → free fall in a → gravitational field or when the net force on it is zero.

Etymology (EN): From → weight + -less suffix meaning “without”

• -ness a suffix of quality or state.

Etymology (PE): Bivazni, from bi- “without,” → a-,

• vazn, → weight, + -i.

A → semiempirical → equation which describes the → binding energy of the → atomic nucleus. It is essentially a nuclear mass formula that provides the total binding energy per → nucleon as the sum of five terms:
E_b = a_VA - a_SA^2/3 - a_CZ²/A^1/3 - a_A(N -Z)²/A + δ(A,Z),
where the terms in the right-hand side of this equation are called the volume term, surface term, Coulomb term, asymmetry term, and pairing term, respectively. A, Z, and N are the number of nucleons, → protons, and → neutrons, respectively
(see, e.g., Alexi M. Frolov, 2013, arxiv.org/pdf/1212.6768). Also called Bethe-Weizacker formula and → semiempirical binding energy formula.

See also: Named after Carl Friedrich von Weizäcker (1912-2007), German physicist, who derived the formula in 1935, Z. für Physik 96, 431; → formula.

1. In a good or satisfactory manner; thoroughly, carefully, or soundly.
   

2. A hole drilled or bored into the earth to obtain water, petroleum, natural gas, brine, or sulfur (Dictionary.com).

Etymology (EN): 1) M.E., from O.E. wel(l) (cognates Du. wel, Ger. wohl).

2. M.E. well(e), O.E. wylle, wella, welle (cognates: O.Saxon wallan, O.Fris. walla, O.H.G. wallan, Ger. wallen “to bubble, boil”).

Etymology (PE): 1) Xoš “good, well, sweet, fair, lovely,” probably related to hu- “good, well,” → eu-. Xub, ultimately from Av. huuāpah- “doing good work,” → operate.

2. Câh “a well,” from Mid.Pers. câh “a well;”
   Av. cāt- “a well,” from kan- “to dig,” uskən- “to dig out;”
   O.Pers. kan- “to dig,” akaniya- “it was dug;” Mod.Pers.
   kandan “to dig;” cf. Skt. khan- “to dig,” khanati “he digs,” kha- “cavity, hollow, cave, aperture.”

A string of → symbols from the alphabet of the → formal language that conforms to the grammar of the formal language. → closed wff, → open wff.

See also: Wff, pronounced whiff; → well; → form; → formula.

A set in which every → nonempty → subset has a minimum element.

See also: → well; → order; → set.

A sequence of → permitted transitions in the → ultraviolet from an → excited state (C) of the → molecular hydrogen (H₂) to the electronic → ground state, with ΔE > 12.3 eV and λ ranging from 1160 Å to 1250 Å. When a hydrogen molecule absorbs such a photon, it undergoes a transition from the ground electronic state to the excited state (C). The following rapid → decay creates an → absorption band in that wavelength range.
See also → Lyman band; → Lyman-Werner photon.

See also: Named after the Danish physicist Sven Theodor Werner (1898-1984), who discovered the band (S. Werner, 1926, Proc. R. Soc. London Ser. A, 113, 107); → band.

The direction 90° to the left or 270° to the right of → north.

Etymology (EN): M.E., O.E. “west” “in or toward the west;” cf. O.N. vestr, O.Fris., M.Du., Du. west, Ger. West; PIE base *wes- (Gk. hesperos, L. vesper “evening, west”).

Etymology (PE): Bâxtar “west;” Mid.Pers. apâxtar “north;” Av. apāxtar “northern.”

Lying toward or situated in the west. → greatest western elongation.

See also: Adjective from → west.

The position of a planet when it is visible in the eastern sky before dawn.

See also: → western; → elongation.

Consisting of, containing, covered or soaked with water or some other liquid.

Etymology (EN): O.E. wæt “moist, liquid,” related to O.Frisian wēt, O.N. vātr, O.E. wæter “water.”

Etymology (PE): Xis, xês “wet, moist,” related to pašang, pašangidan “sprinkle,” ultimately from Proto-Ir. *haic- “to pour (out), moisten;” cf. Av. haēc- “to pour (out); to irrigate;” Khotanese häs- “to wet, besprinkle;” Sogd. šync “to pour” (Cheung 2007).

A merger between → gas-rich galaxies. Wet mergers may lead to enhanced star formation, trigger → active galactic nuclei, and transform a → disk galaxy into an → elliptical galaxy. The larger the → redshift, the wetter mergers should be.

See also: → wet; → merger.

The → world lines of galaxies form in the 4D space-time
a bundle of non-intersecting → geodesics orthogonal to a series of space-like hyperstructures (e.g. Narlikar 2002, An Introduction to Cosmology, 3rd Edition, Cambridge Univ. Press). Expressed differently: The world lines of galaxies, or “fundamental particles,” form (on average) a space-time filling family of non-intersecting geodesics converging toward the past (Rugh & Zinkernagel, 2010, astro-ph/1006.5848). The statement is sometimes denoted postulate, assumption, or hypothesis. The importance of Weyl’s principle is that it asserts that cosmic matter moves according to certain regularity requirements. See also → cosmological principle.

See also: First introduced by the German mathematician Hermann Weyl (1885-1955) in 1923 in his Raum, Zeit, Materie; → principle.

The star δ Canis Majoris, magnitude 1.84. It is an F8 supergiant 1800 light-years away. Among bright stars, Wezen is one of the most distant and luminous. Its luminosity is 50,000 times that of the Sun. Other designations: Alwazn, Wesen, HR 2693, HD 54605.

Etymology (EN): From Ar. Al-wazn (الوزن) “weight.”

Etymology (PE): Vazn, from Ar. Al-wazn, as above.

1. Any of the larger ocean mammals, excluding the porpoises and dolphins, that breathe through a blowhole on the top of their head and have front flippers, no hind limbs, and a flat horizontal tail.
   

2. The constellation → Cetus.

Etymology (EN): M.E., O.E. hwæl, cf. O.S. hwal, O.N. hvalr, Swed. val, M.Du. wal, Du. walvis, O.H.G. wal, Ger. Wal, probably cognate with L. squalus and Pers. vâl, as below.

Etymology (PE): 1) Mod.Pers. vâl, wâl, related to Mid.Pers. kar (mâhig) “whale (fish);” Av. kara- “a mythological fish;” also Mod.Pers. kuli “a kind of fish;” cf. L. squalus “a kind of large sea fish;” PIE (s)k^walo- “a large fish.”

2. Pers. nahang originally “crocodile,” from Mid.Pers. nihang “crocodile; hippopotamus,” ultimately from Proto-Iranian *ni-θanj- “to drag down,” since crocodiles drag down their preys
   underwater and drown them, from ni- “down, below,” → ni- (PIE) , + θanj- “to draw, pull” (cf. Pers. farhang; sanjidan, etc.).

An device consisting of four → resistances in series, used to determine the value of an unknown electrical
resistance when the other three resistances are known.

See also: Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge.

1. A solid disk or a rigid circular ring arranged to turn around an axle passed through the center.
   

2. Anything like a wheel in shape or function.

Etymology (EN): M.E. whel(e), O.E. hweol, hweogol,
from PIE *k(w)e-k(w)lo- “wheel, circle;” cf. Gk. kyklos “circle, wheel;” L.L. cyclus; Mod.Pers. carx “wheel;”
Av. caxra- “wheel;” Skt. cakra- “wheel, circle;” Rus. koleso “wheel.”

Etymology (PE): Carx “wheel,” akin to wheel, as above.

In → quantum gravity, an equation that describes the → wave function of the → Universe. It is an adaptation of the → Schrodinger equation but includes the curved space attributes of → general relativity.

See also: Named after American theoretical physicists John Archibald Wheeler (1911-2008) and Bryce Seligman DeWitt (1923-2004).

1. To turn around or spin rapidly.
   

2. The act of whirling; rapid rotation. → whirlwind, → whirlpool, → dust whirl.

Etymology (EN): M.E. whirlen, from O.N. hvirfla “to whirl,” akin to O.E.
hwyrflung “turning, revolving.”

Etymology (PE): → rotate; → revolve.

A powerful water current moving rapidly in a circular manner, as that produced by the meeting of opposing currents, sucking down anything that comes within. → Whirlpool galaxy.

Etymology (EN): From whirl “to turn around,” from M.E. whirlen, from O.N. hvirfla “to whirl,” cognate with O.E. hweorfan “to turn;”

• → pool “a body of water.”

Etymology (PE): Gerdâb “whirlpool,” from gerd from gardidan “to turn” (→ -tropic) + âb, → water.

A large → spiral galaxy of type Sc seen → face-on in the constellation → Canes Venatici and lying about 31 million → light-years away. Also known as M51 and NGC 5194. It is interacting with a small irregular galaxy NGC 5195.

See also: → whirlpool; → galaxy.

A general term for a small-scale, rotating column of air. More specific terms are → dust whirl, → dust devil, → waterspout, and → tornado.

See also: → whirl; → wind.

A whistling sound of descending pitch picked up by radio telescopes under certain circumstances. Whistlers are caused by radio waves from distant lightening flashes, which follow the lines of force of the Earth’s magnetic field and are reflected back to Earth by the → ionosphere.

Etymology (EN): From M.E. whistler,; O.E. hwistlere, from hwistlian “whistle.”

Etymology (PE): Sutzani “whistling,” from <isut “whistle,” probably onomatopoeia + zani verbal noun from zadan “to make, to do,” originally “to strike, beat; to do; to play an instrument” (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- “to strike, hit, smite, kill” (jantar- “smiter”); cf.
Skt. han- “to strike, beat” (hantar- “smiter, killer”);
Gk. theinein “to strike;” L. fendere “to strike, push;” Gmc. *gundjo “war, battle;” PIE *g^when- “to strike, kill”).

Having the color of fresh snow or milk; reflecting nearly all the rays of sunlight. → white dwarf; → night.

Etymology (EN): M.E. whit(e); O.E. hwit, from P.Gmc. *khwitaz (cf. O.S., O.Fris. hwit, O.N. hvitr, Du. wit, O.H.G. hwiz, Ger. weiß, Goth. hveits); cognate with Pers. sefid, as below.

Etymology (PE): Sefid, sepid “white;” Mid.Pers. spêt; Av. spita- “white;” cf. Skt. śveta- “white;” Lith. sviesti “to shine,” svaityti “to brighten;” cognate with E. white, as above.

A compact star of high surface temperature, low luminosity, and high density (10⁵-10⁸ g cm^-3), with roughly the mass of the Sun (mean mass ~ 0.6 M_sun) and the radius of the Earth (R ~ 0.01 R_sun), representing the end-point of the evolution of all stars with masses less then ~ 5-9 → solar masses. A white dwarf is what remains after the central star of a → planetary nebula fades and becomes cool. The → Chandrasekhar limit of 1.43 solar masses is the highest mass that a white dwarf can achieve before electron → degeneracy pressure is unable to support it. In the → Hertzsprung-Russell diagram, white dwarfs form a well-defined sequence around 8 magnitudes fainter than the main sequence.
They are composed of a core of carbon and oxygen nuclei and degenerate electrons surrounded by a thin shell of helium and an outer skin of hydrogen. White dwarf’s radiation is the leftover heat from the star’s past when its core was an active nuclear reactor. The star slowly cools as heat escapes through the non-degenerate envelope. → white dwarf crystallization; → cooling time; → Mestel theory. The first white dwarf to be discovered was Sirius B, the → companion of Sirius. White dwarfs are divided into several types, according to their spectral features, which depend on the type of → shell burning that dominated as it became a → planetary nebula: → DA white dwarf; → DB white dwarf; → DC white dwarf; → DO white dwarf; → DZ white dwarf; → DQ white dwarf. For a review see Kepler and Brdaley (1995, Baltic Astron. 4, 166).

See also: The term white dwarf was coined by the Dutch-American astronomer Willem Luyten (1899-1994) in 1922, from → white + → dwarf.

In the → Hertzsprung-Russell diagram, the evolutionary track followed by a → low-mass or an → intermediate-mass star when it can no longer produce thermonuclear energy. The track starts at the end of the → horizontal branch to lead the star to a → white dwarf phase.

See also: → white; → dwarf; → cooling; → track.

The most important phenomenon occurring during → white dwarf evolution, which results from its cooling. Crystallization is a → phase transition whereby → latent heat is released. At the cooler end of a white dwarf’s life (→ cooling time), the
→ thermal energy of nuclei, which are positively charged ions, becomes small and the effects of electrostatic interaction on the motion of ions become important. The ions repel each other and their distribution will be such that the → Coulomb energy per ion is a minimum. This will cause the ions to form crystal-like lattice structures. As the star cystallizes it releases latent heat, providing an additional energy source that slows the cooling process compared to the → Mestel theory. Once the bulk of the white dwarf is crystalline, heat can travel through the star more easily and the white dwarf cools faster.

See also: → white; → dwarf; → crystallization.

A hypothetical opposite of the → black hole, from which particles and light pour out. However, there is a basic problem with white holes. Contrarily to black holes, no physical processes justify their existence. The appearance of a white hole is not due to any cause, it is acausal.

See also: → white; → hole.

The circumstance pertaining to polar latitudes in which when the Sun sets its center does not go beyond 6° below the horizon and the → twilight lasts all the night.

See also: → white; → night.

A random signal that has a relatively wide continuous range of frequencies of uniform intensity.

See also: → white; → noise.

For what cause or reason? On what account? wherefore; on account of which.

Etymology (EN): M.E., from O.E. hwi, hwy instrumental case of hwæt “who.”

Etymology (PE): Cerâ, from Mid.Pers. ce rây “why; how,” from cê “what” (→ because) + rây, → reason.

Having considerable or great extent from side to side; broad. → wide binary, → wide field.

Etymology (EN): From M.E., from O.E. wid; akin to Du. wijd, Ger. weit, Old Norse vithr.

Etymology (PE): Bozorg, → large.
Gošâd, gošâdé “opened; ample, broad,” from gošudan “to open up, to loose,” → resolve.

An international collaboration, more accurately named SuperWASP, led by the United Kingdom, that aims at detecting → extrasolar planets by means of the → transit method.

SuperWASP consists of two robotic observatories that operate continuously all year around, providing coverage of the sky in both hemispheres. The first, SuperWASP-North, is located on the island of La Palma. The second, SuperWASP-South, is located at the site of the South African Astronomical Observatory (SAAO). The observatories each consist of eight wide-angle cameras that simultaneously monitor the sky for → planetary transit events. Using the array of cameras makes it possible to monitor millions of stars simultaneously at an → apparent visual magnitude from about 7 to 13.

See also: → wide; → angle; → search; → planet.

A binary system with semi-major axis as large as 10,000 → astronomical units.

See also: → wide; → binary.

A telescope → field of view which covers a relatively large → angular area on the sky.

See also: → wide; → field.

A → NASA infrared astronomical → space telescope launched in December 2009 to carry out an → all-sky survey from 3 to 22 → microns. With its 40-cm → telescope telescope and → infrared cameras, WISE aimed at a wide variety of studies ranging from the evolution of → protoplanetary disks to the history of → star formation in normal galaxies. In early October 2010, after completing its prime science mission, the spacecraft ran out of → coolant that keeps its instrumentation cold. However, two of its four infrared cameras remained operational. Hence,
NASA extended the NEOWISE portion of the WISE mission by four months, with the primary purpose of hunting for more → asteroids and → comets,
and to finish one complete scan of the main → asteroid belt. In August 2013, the WISE telescope’s mission was extended for more three years to search for asteroids that could collide with Earth.

See also: → wide field; → infrared; → survey; → explorer.

An extent from side to side; breadth; wideness.
→ bandwidth; → beamwidth; → equivalent width; → slitwidth.

Etymology (EN): From wide, M.E., O.E. wid (cf. Du. wijd, O.H.G. wit, Ger. weit) + -th a suffix forming nouns of quality or condition, M.E. -th(e); O.E. -thu, -th.

Etymology (PE): Pahnâ, from pahn “wide, broad,” from Mid.Pers. pah(a)n; Av. paθana- “broad, wide, spacious.”

For all metals the ratio of the → thermal conductivity, κ, to the → electrical conductivity,
σ, is directly proportional to the absolute temperature: K/σ = (1/3)(πk/e)²T, where k is → Boltzmann’s constant and e the electron’s charge.

See also: Named after the German physicists Gustav Heinrich Wiedemann (1826-1899) and Rudolph Franz (1826-1902); → law.

The wavelength corresponding to the maximum emissive power of a black body is inversely proportional to the absolute temperature of the body: λ_max.T = 0.29 cm-deg. Wien’s law explains why objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer. Wien’s law was an early attempt to describe the → blackbody radiation.
The law closely approximated the true shape of the blackbody spectrum at short wavelengths, but ultimately failed because it relied solely on classical physics. It was superseded by → Planck’s radiation law, which correctly describes the blackbody spectrum at all wavelengths.

See also: After the German physicist Wilhelm Wien (1864-1928), who found the law in 1896. He was awarded the 1911 Nobel Prize in physics; → displacement; → law.

A theorem used in signal processing whereby the → spectral density of a random signal is the → Fourier transform of the corresponding → autocorrelation function. In other words, the autocorrelation function and the spectral density function constitute a → Fourier transform pair. The Wiener-Khinchin theorem allows one to estimate the spectral density function from the Fourier transform of the autocorrelation function, which is easier to handle. The theorem has an important application particularly
in radio astronomy. The two following → Fourier integrals are called the Wiener-Khinchin relations: K(τ) = ∫ J(f)e^-iωτdf and J(f) = ∫ K(τ)e^iωτdτ (both summed over -∞ to +∞), where K(τ) is the autocorrelation function and J(f) is the spectral density.

See also: Named after Norbert Wiener (1894-1964), American mathematician, who
first published this theorem in 1930, and Aleksandr Khinchin (1894-1959), Russian mathematician, who did so independently in 1934; → theorem.

Living in a state of nature; not tamed or domesticated (Dictionary.com).

Etymology (EN): M.E., from O.E. wilde; cognate with Du., O.H.G. wildi, Ger. wild, Sw. vild.

Etymology (PE): Towsan “wild,” cf. Av. disav- “a kind of night predator animal.”

Animals and plants living in their natural habitat.

See also: → wild; → life.

A space telescope launched by NASA in 2001 which measures the temperature fluctuations in the → cosmic microwave background (CMB) radiation.
It creates a full-sky map of the CMB, with a 13 arcminute resolution via multi-frequency observations. WMAP is the first mission to use a → Lagrangian point L2 as its permanent observing station at a distance of 1.5 million km. WMAP completed its prime two years of mission operations in September 2003 and is continuing in 2009 its observations for still several years to come. WMAP’s measurements have played a considerable role in establishing the current standard model of cosmology. They are consistent with a Universe that is dominated by → dark energy, with negative pressure or a → cosmological constant. In this model, the age of the Universe is 13.73 ± 0.12 billion years. The current expansion rate of the Universe measured by the Hubble constant, is 70.5 ± 1.3 km·s^-1 Mpc^-1. The content of the Universe consists of 4.56% ± 0.15% ordinary → baryonic matter, 22.8% ± 1.3% → cold dark matter, and 72.6% ± 1.5% of → dark energy, that accelerates the → expansion of the Universe.

See also: WMAP, short for Wilkinson Microwave Anisotropy Probe, in honor of David Todd Wilkinson (1935-2002), who had been a member of the mission’s science team.

The depression on the → Sun’s → photosphere associated with → sunspots and involving the → Wilson effect. The measured depression values vary between about 700 and 2,000 km.

See also: → Wilson effect; → depression.

A phenomenon in which the shape of → sunspots flattens as they approach the → Sun’s limb due to the → solar rotation. More specifically, when a sunspot approaches the → solar limbs the width of the → penumbra, relative to the → umbra, on the side facing the center of the Sun seems to become narrower than on the side facing the limb. This phenomenon arises from a projection effect, and is due to a geometrical depression (the → Wilson depression) in the layers of constant → optical depth in sunspots (see, e.g., Sami K. Solanki, 2003, Sunspots: An overview, The Astron. Astrophys. Rev., 11, 153).

See also: First noticed by Alexander Wilson (1714-1786); → effect.

The strong correlation between the equivalent width of Ca II → H and K lines of a late-type giant or supergiant star with the absolute visual magnitude of the star.

See also: O. C. Wilson & M. K. Vainu Bappu (1957, ApJ 125, 661); → effect.

A member of a broad class of hypothetical elementary particles moving with non-relativistical speeds at the time of structure formation in the early Universe. WIMPs have nonzero rest mass and participate only in the weak nuclear interaction. WIMPs are expected to have collapsed into a roughly isothermal, spherical halo within which the visible portion of our galaxy resides. → dark halo. The → neutralino, predicted by supersymmetric theories is the favorite WIMP candidate. Another candidate is the → axion. WIMPs are candidates for dark matter.

See also: → weak; → interction; → massive; → particle .

1a) Meteo.: Air in motion, especially a natural and perceptible movement of air
relative to the ground.

1b) Astro.→ radiation-driven wind; → solar wind; → Galactic wind; → stellar wind.

2. To change direction; turn; to have a circular or spiral course or direction; to coil or twine about something.

Etymology (EN): 1) M.E., O.E. wind (cf. O.S., O.Fris., Du. wind, O.H.G. wind, Ger. Wind, Goth. winds).

2. M.E. windan, from O.E. windan “to turn, twist, curl,” cognate with Du. winden, O.H.G. wintan, Ger. winden, from PIE *wendh- “to turn, wind, weave.”

Etymology (PE): 1) Bâd, from Mid.Pers. wâd “wind;” Av. vāta- “wind;” cf. Skt. vāta- “wind, god of wind;” Gk. anemos “wind;”
L. ventus “wind” (Fr. vent); cognate with E. wind, as above.

2. Picidan “to twist, entwine, coil,” → spiral.

A quasi-spherical accretion that is likely to occur in a → high-mass X-ray binary (HMXB) when the optical star of → early spectral class (O-B) does not fill its → Roche lobe, but has a significant → mass loss via → stellar wind. In → close binary systems another accretion regime, → disk accretion, occurs when the optical star overfills its Roche lobe.

See also: → wind; → accretion.

A process whereby dense winds of very luminous O type stars modify the temperature and internal structure of the underlying photosphere by scattering back a considerable part of the coming photospheric radiation. Not to be confused with → line blanketing .

See also: Thus called because the wind acts like a blanket and heats the photosphere * by reflecting its radiation; → wind.

The inhomogeneous property of a → radiation-driven wind, or the physical mechanism accounting for the → clumped wind.

See also: → clumpy; → wind.

The final kinetic energy of the → stellar wind expressed by:

(1/2)Mdot.v_∞² = (1/2)(v_∞/c)L

For an O6 star, L ~ 3 x 10⁵Lsun and v_∞ ~ 2000 km s^-1, which give a wind luminosity of ~ 1 x 10³⁷ erg s^-1, about 1% of the → stellar luminosity. See also → photon tiring limit.

See also: → wind; → luminosity.

The product of the → mass loss rate and → terminal velocity used in the → radiation-driven wind theory. See also → modified wind momentum.

See also: → wind; → momentum.

A diagram showing the relative frequency of winds blowing from each of the 8 or 16 main points of the compass, sometimes within specified speed ranges, at a given location over a considerable period.

Etymology (EN): Translation of Ger. Windrose “compass card,” from Wind→ wind + Rose “rose,” → Rosette Nebula.

Etymology (PE): Bâdnaqš, from bâd, → wind, + naqš “painting, engraving, printing,” → map.

An object that is balanced on a rotating axis and indicates the direction of the wind. Also called a weather vane.

Etymology (EN): → wind + vane “a blade, plate,” O.E. fana</i< “flag, weather-cock;” cf. Goth. fana “piece of cloth,” O.H.G. fano, Ger. Fahne “flag, standard.”

Etymology (PE): Bbâdnemâ “wind indicator,” from bâd, → wind, + nemâ, from nemudan, → planetarium.

The speed at which the → stellar wind is forced away from the star. Wind velocities of → hot stars are directly measured from → P Cygni profiles, which indicate velocities from several hundred to several thousand km s^-1. See also → escape velocity, → terminal velocity, → velocity law, → radiation-driven wind, → CAK model.

See also: → wind; → velocity.

The problem encountered in the explanation of the → spiral arms of galaxies if the material making up a spiral arm is static, that is
remains in the arm. Since galaxies exhibit → differential rotation, stars near the center take less time to orbit the center than those farther from the center. The arm would, after a few → galactic rotations, become increasingly curved and wind around the → galaxy ever tighter until it ultimately disappears. This is inconsistent with observations.

1. Anything likened to a window in appearance or function.
   
2. In particular, the wavelength region in the electromagnetic spectrum that is relatively unaffected by atmospheric absorption. → atmospheric windows; → infrared window; → optical window; → radio window.

Etymology (EN): Window literally “wind eye,” from O.N. vindauga, from vindr, → wind, + auga,
→ eye.

Etymology (PE): Rowzané, from rowzan “window, aperture;” Mid.Pers. rocânak “window,” rôšn “light; bright, luminous,” from Av. raocana- “bright, shining, radiant,” raocah- “light, luminous; daylight,” related to Mod.Pers. ruz “day,” from Mid.Pers. rôc, O.Pers. raucah-; akin to Skt. rocaná- “bright, shining,” roka- “brightness, light;” Gk. leukos “white, clear;” L. lux “light” (also lumen, luna); PIE base *leuk- “light, brightness.” The Persian words rowšan “bright, clear,” foruq “light,” and afruxtan “to light, kindle” also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière; forusorx→ infrarouge.

A function whose value is zero outside a given interval. Applications of window functions include signal filtering and spectral analysis. The various types of windw functions include: → rectangular window, cosine window, triangular window, Gaussian window, Hanning window, and so on.

See also: → window; → function.

The fermented juice of grapes, made in many varieties, such as red, white, sweet, dry, still, and sparkling, for use as a beverage, in cooking, in religious rites, etc., and usually having an alcoholic content of 14 percent or less (Dictionary.com).

Etymology (EN): M.E., O.E. win, cognate with O.H.G. win, Du. wijn, Ger. Wein, from L. vinum “wine,” from PIE *woin-o-, related Gk. word oinos.

Etymology (PE): Mey, variant mol “wine;” Mid.Pers. mad, may “wine;” Av. maδu- “wine;” cf. Skt. madhu- “wine, sweet drink, sweet;” Gk. methy “wine;” O.C.S. medu; Lith. medus “honey;” O.Irish mid; Welsh medd; Breton mez “mead;” O.E. medu; E. mead “fermented honey drink;” Russ. medved “(honey-eater) bear.”
Bâdé, from Mid.Pers. bâdag, from O.Pers. *bātu- “wine” (from bātu-gara- “cup, bowl”); cf. Khotanese Saka bātaa- “wine;” O.Pers. *batiaka- “cup, bowl” (cf. Pers. bâdiyé “bowl”) loaned in Gk. batiaké “bowl, cup.”
Nabid, “wine, date-wine,” ultimately from Proto-Ir. *paH- “to drink;” cf. Av. paitīš- “drink” in vīspô.paitīš- “having all sorts of drinks;” pitu- “juice, food;” Wakhi puv-, pəv-, pit-; Sanglechi pöv-/pövδ- “to drink;” Skt. pā- “to drink;” Gk. pinein “to drink;” L. bibere “to drink,” related to potare “to drink.”

1. Either of the two limbs of a bird allowing her to fly. → Pegasus.
   

2. Either of the large flat structures in an aircraft’s body that provide the main source of lift.
   

3. In spectroscopy, same as → line wing.

Etymology (EN): M.E. wenge from O.N. vængr “wing of a bird, aisle, etc.” (cf. Dan., Swed. vinge “wing”).

Etymology (PE): Bâl “wing,” Mid.Pers. bâl, variant of par / parr “feather, " with the conversion of p to b and r to l; Av. parəna- “feather;” cf. Skt. parnam;
O.H.G. farn “fern;” PIE pornom “feather.”

A spectral feature at 9850-10200 Å appearing in the spectrum of some late-type → M dwarfs. It is attributed to iron hybrid (FeH), a typical signature of the atmospheres of the coolest stars.

See also: First detected by R. F. Wing and W. K. Ford (1969, PASP 81, 527); → band.

The season beginning at the → winter solstice, about December 22 and lasting until the → vernal equinox, about March 21.

Etymology (EN): M.E., OE; cf. O.Fris., Du. winter, O.S., O.H.G. wintar, Ger. winter, Dan., Swed. vinter, Goth. wintrus “winter”),

Etymology (PE): Zemestân “winter,” related to zam “cold,” Mid.Pers. zam, zamistân “winter;” Av. zimô “winter;” cf. Skt. hima- “cold, frost;” Ossetic zymæg/zumæg “winter;” Gk. xeimon “winter;” L. hiems “winter;” Lith. ziema “winter;” PIE *gheim- “snow, winter.”

The moment in the northern hemisphere when the → Sun attains its lowest → declination of -23°26’ (or -23°.44) with respect the → equator plane. It happens when the Earth’s axis is orientated directly away from the Sun, on 21 or 22 December. During the northern winter solstice the Sun appears to be directly overhead at noon for places situated at → latitude 23.44 degrees south, known as the → tropic of Capricorn. The winter solstice can occur at any moment during the day. Two successive winter solstices are shifted in time by about 6 h. The winter solstice in the northern hemisphere is the → summer solstice in the southern hemisphere.

See also: → winter; → solstice..

A slender flexible thread or rod of metal.

Etymology (EN): M.E., O.E. wir, cf. O.N. viravirka “filigree work,” Swed. vira “to twist,” O.H.G. wiara “fine gold work.”

Etymology (PE): Sim “wire,” initially “strand of silver,” from sim “silver,” from Mid.Pers. asêm “silver,” from Gk. asemon “without mark, uncoined, shapeless, formless,” from argurion asemon “uncoined money.” For semantic similarity, see → silver.

The quality or state of being → wise; knowledge of what is true or right coupled with just judgment as to action; sagacity, discernment, or insight (Dictionary.com). Wisdom is gained over the years through experience. It is the insight in knowing the probable outcome learned through experience. In contrast, → reason is using the → rational → reasoning to evaluate pros and cons in making a decision.

Etymology (EN): M.E.; O.E. wisdom, from wis “→ wise”

• -dom. The first component is related to → vision and Pers. bin, didan “to see.”

Etymology (PE): Xerad “understanding, judjement, intellect, wisdom;” Mid.Pers. xrad “reason, intellect, intelligence, wisdom, understanding;” O.Pers. xraθu- “wisdom;” Av. xratu- “intelligence, understanding, wisdom; will, purpose, council;” cf. Skt. krátu- “power, will-power;” Gk. kratos “power, strength.”

Having the power of discerning and judging properly as to what is true or right; possessing discernment, judgment, or discretion (Dictionary.com).

Etymology (EN): From M.E. wis, wys, from O.E. wis (“wise”), cognate with Du. wijs, Ger. weise, Norw. and Swed. vis.

Etymology (PE): Xeradmand, from xerad, → wisdom,

• -mand relatrion and possession suffix.

A → Wolf-Rayet star whose spectrum is dominated by emission lines of ionized nitrogen: N II 3995 Å, N III 4634-4661 Å, N III 5314 Å, N IV 3479-3484 Å, N IV 4058 Å, N V 4603 Å, N V 4619 Å, and N V 4933-4944 Å. This type is divided in sub-types WN2 to WN11.

See also: W short for Wolf-Rayet star, N for → nitrogen.

An object showing signatures of both → WN Wolf-Rayet stars and → WC Wolf-Rayet stars
in the same spectrum, originating from individual stars rather than from WN + WC → binary systems. Such a WN/WC signature implies that the surface composition of the star is → nitrogen and → carbon enriched. This hybrid state results from a mixing process between He-burning → convective core and the overlying nitrogen enriched layers. According to model predictions, this situation corresponds to a short transition phase, lasting 10³ to 10⁴ years, during which a WN star evolves into a WC star. The WN/WC stars so far detected are all of early types.

See also: → WN Wolf-Rayet; → WC Wolf-Rayet.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å as strong as N II 3995 Å, Balmer lines, He I with → P Cygni profile.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N II 3995 Å as strong as He II 4686 Å, N III 4634-4641, 5314 Å weak or absent, Balmer lines, He I with → P Cygni profile.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N V 4603, 4619 Å weak or absent,He II 4686 Å strong.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N V 4603, 4619 Å present, N IV 3479-3484, 4058 Å absent.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N IV 3479-3484, 4058 Å very weaker than N V 3479-3484, 4058 Å and N III 4634-4641, 5314 Å weak or absent.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A new type of → Wolf-Rayet stars found in the → Large Magellanic Cloud (LMC). These stars have both strong → emission lines, as well as → He II lines and → Balmer lines in absorption and spectroscopically resemble a → WN3 and → O3V binary pair. However, they are visually too faint to be WN3+O3 V → binary systems. So far nine WN3/O3 types have been detected, making up ~ 6% of the population of LMC WRs. Their temperatures are estimated to be around 100,000 K, a bit hotter than the majority of → WN Wolf-Rayet stars (by around 10,000 K) although a few hotter WNs are known. The abundances are what you would expect for → CNO equilibrium. However, most anomalous are their → mass-loss rates which are more like that of an → O star than a WN star. While their evolutionary status is uncertain, their low mass-loss rates and → wind velocities suggest that they are not products of homogeneous evolution. It is possible instead that these stars represent an intermediate stage between O stars and WNs. Since WN3/O3 stars are unknown in the Milky Way, their formation would depend upon → metallicity (Neugent et al., 2017, arxiv:1704.05497).

See also: → WN3; → O3; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N IV 3479-3484, 4058 Å about N V 3479-3484, 4058 Å and N III 4634-4641, 5314 Å
weak or absent.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N IV 3479-3484, 4058 Å stronger than N V 3479-3484, 4058 Å and N III 4634-4641, 5314 Å weak or absent.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å as strong as N IV 3479-3484, 4058 Å as strong as N V 3479-3484, 4058 Å.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å about N IV 3479-3484, 4058 Å and N V 3479-3484, 4058 Å present, but weak.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WNh type → Wolf-Rayet (→ WN6 star) with → absorption lines in its spectrum that have not been attributed to the presence of a → companion. For example → NGC 3603-A1.

See also: The letter “a” indicating → absorption; → WNh type.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å stronger than N IV 3479-3484, 4058 Å, N III weaker than He II 4686 Å, He I weak with → P Cygni profile.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å very stronger than N IV 3479-3484, 4058 Å,
N III about He II 4686 Å, and He I with → P Cygni profile.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å stronger than N II 3995 Å, N IV 3479-3484, 4058 Å absent, He I with → P Cygni profile.

See also: W, from → Wolf-Rayet; N, from → nitrogen; → star.

In theoretical models, a → Wolf-Rayet star without hydrogen at its surface (< 10^-5 in number) and with surface carbon abundance smaller than nitrogen abundance.

See also: W short for Wolf-Rayet star, N for → nitrogen, E for early.

A → WN Wolf-Rayet star which is hydrogen rich. WNh stars are initially more massive and have lost relatively little mass compared to other WR stars. It is suggested that these types are core hydrogen burning → main sequence objects. The most massive stars currently known are all WNh stars rather than O-type main sequence stars.

See also: WN, from → WN Wolf-Rayet; h, from → hydrogen.

In theoretical models, a → Wolf-Rayet star with hydrogen at its surface (> 10^-5 in number). A star enters the Wolf-Rayet phase as a WNL, then may evolve through the sequence WNL → WNE, → WC, → WO. It can end its evolution at any of these stages.

See also: W short for Wolf-Rayet star, N for → nitrogen, L for late.

A → Wolf-Rayet star whose spectrum shows emission lines of carbon and strong emission lines of oxygen O VI 3811-34 Å. In theoretical models, a W-R star whose carbon abundance at surface is larger than nitrogen abundance and has the abundance ratio (C + O) / He > 1 (in number).

See also: W short for Wolf-Rayet star, O for → oxygen.

An oxygen-rich → Wolf-Rayet star whose spectrum shows the following emission line characteristics:
No O IV 3400 Å, strong O VI 3811-34 Å, O V 5572-98 Å about or stronger than C IV 5801-12 Å, no C III 5696 Å.

See also: W, from → Wolf-Rayet; O, from → oxygen; → star.

An oxygen-rich → Wolf-Rayet star whose spectrum shows the following emission line characteristics: No O IV 3400 Å, strong O VI 3811-34 Å, O V 5572-98 Å weaker than C IV 5801-12 Å, no C III 5696 Å.

See also: W, from → Wolf-Rayet; O, from → oxygen; → star.

1a) To incline to one side and to the other alternately, as a wheel, top, or other rotating body when not properly balanced.

1b) To move unsteadily from side to side; vacillate; waver.

2. A wobbling movement (Dictionary.com).

Etymology (EN): Probably from Low Ger. wabbeln “to wobble;”
cognate with O.N. vafla “hover about, totter,” related to vafra “move unsteadily.”

Etymology (PE): Palâpel “wobbling, unsteady motion” in štiyâni dialect, variant in colloquial Persian pilipili, pelpel (pilipili raftan, pilipili xordan).

A 70-year period of unusually low → solar activity, from about 1280 to 1350. See also the → Maunder minimum.

See also: → Wolf number; → minimum.

A number indicating the degree of → sunspot  → activity. Same as → sunspot number and → relative sunspot number.

See also: Named after Johann Rudolf Wolf of Zurich who introduced the number in 1852; → number.

A → dwarf irregular galaxy that is a remote and rather isolated member of the → Local Group. Also known as DDO 221 and LEDA 143. It is a dim galaxy located in the constellation → Cetus, about three million → light-years from the → Milky Way. Its nearest neighbor, the → dwarf galaxy IC 1613, is one million light-years away. Quite elongated, with a largest extension of more than 8,000 light-years, WLM is about 12 times smaller than the Milky Way, a measurement that includes a → halo of extremely → old stars. WLM has a → metallicity only about one-tenth that of the Milky Way.

See also: Named after astronomer Max Wolf (1863-1932), who discovered the galaxy in 1909, and astronomers Knut Lundmark (1889-1958) and Philibert Jacques Melotte (1880-1961), who identified it as a galaxy some fifteen years later.

A subset of → starburst galaxies whose integrated spectra show broad emission features attributed to the presence of hundreds to thousands
→ Wolf-Rayet stars. The most massive stars formed in the burst evolve rapidly into a substantial population of Wolf-Rayet stars in aggregations of ionized gas.

See also: → Wolf-Rayet star; → galaxy.

A type of very luminous, very hot (as high as 50,000 K) stars whose spectrum is characterized by broad emission lines (mainly He I and He II), which are presumed to originate from material ejected from the star at very high (~ 2000 km s^-1) velocities. The most massive → O stars (M > 25 → solar masses for → solar metallicity) become W-R stars around 2 and 3 million years after their birth, spending only some few hundreds of thousands of years (≤ 10⁶ years) in this phase until they explode as → type Ib and → type Ic supernovae. The minimum stellar mass that an O star needs to reach the W-R phase and its duration is dependent on → metallicity. → WC Wolf-Rayet; → WNE Wolf-Rayet; → WNL Wolf-Rayet; → WO Wolf-Rayet. For a review see: P. A. Crowther, 2007, Annu. Rev. of Astron. Astrophys. 45, 177.

See also: Named after the French astronomers Charles Wolf (1827-1918) and Georges Rayet (1839-1906), of the Paris Observatory.
In 1867 they discovered three stars in the constellation Cygnus (now designated HD191765, HD192103, and HD192641), that displayed broad emission bands in their spectra; → star.

An optical device for producing and analyzing polarized light. It divides
incoming unpolarized light into two orthogonal, linearly polarized beams. It consists of two prisms of either quartz or calcite cemented together.

See also: After the English scientist William Hyde Wollaston (1766-1828); → prism.

A → grazing incidence telescope designed to observe → X-ray emission from astronomical objects. Wolter telescopes use a combination of two elements, a parabolic mirror followed by a hyperbolic mirror and come in three different optical configurations.

The design most commonly used by X-ray astronomers is the Type I since it has the simplest mechanical configuration. In addition, the Type I design offers the possibility of nesting several telescopes inside one another, thereby increasing the useful reflecting area. This is an extremely important attribute, since virtually all X-ray sources are weak, and maximizing the light-gathering power of a mirror system is critical. The → Chandra X-Ray Observatory is a Wolter Type I telescope that has four thick nested mirrors coated in iridium. The Japanese X-ray observatory Suzuki uses a conical approximation of the Wolter Type I design. Its mirrors are coated in gold, and they are far thinner than the ones used in Chandra. This allows for denser nesting, so there are 700 mirrors instead of four. The result is a much higher collecting efficiency at a reduced weight.

For comparable apertures and grazing angles, the primary advantage of Type II over Type I is that higher magnifications are attainable. This is because the second reflection is off the outside of a surface, which allows longer focal lengths. However, since off-axis images suffer much more severely from blurring in Type II configurations, the Wolter Type II is useful only as a narrow-field imager or as the optic for a dispersive spectrometer. The Wolter Type III has never been employed for X-ray astronomy (NASA Imagine the Universe!).

See also: Named after Hans Wolter (1911-1978), a German physicist who designed the optical configuration.

In → magnetohydrodynamics, in the limit of zero → resistivity, the → magnetic field  B satisfies the → induction equation  ∂B/∂t = ∇ x (v x B), then for a → plasma confined by a perfectly conducting boundary, the → magnetic helicity is conserved. If the normal field is fixed on the boundary, the minimum-energy state is the linear → force-free magnetic field that conserves the total magnetic helicity.

See also: Named after the Dutch astrophysicist Lodewijk Woltjer (1930-2019), who discovered the phenomenon in 1958 while studying the → Crab Nebula; → theorem.

The → female human being.

Etymology (EN): M.E. womman, wimman, O.E. wifman, from wif “female” + man “human being.”

Etymology (PE): Zan “woman, wife” (variants Baluci, Zâzâ jan, Gorgâni cen, Baxtiyâri zine, Sangesari, Tâti, Kurd. žen, Kurd. kenâ, Karingâni yan); Mid.Pers. zan “woman, wife;” kaniz “maid, virgin, girl;” Av. jəni- “woman, wife;” cf. Skt. jáni- “woman, wife;” Gk. gyne “woman, wife;” O.E. cwen “queen, woman, wife” (E. queen; Arm. kin “woman;” PIE base *g^wenh- “woman, wife.”

A unit of language, consisting of one or more sounds or their written representation, that communicates a meaning. → stopword

Etymology (EN): M.E., from O.E. word; cf. Du. woord, O.H.G., Ger. wort, Goth. waurd; related to verb, from L. verbum “verb;” from PIE *wer- “to speak, say.”

Etymology (PE): Vâžé “word;” Mid.Pers. vâc, vâcak “word, speech;” related to âva “voice, sound,” âvâz “voice, sound, song,” bâng “voice, sound, clamour” (Mid.Pers. vâng); Av. vacah- “word,” vaocanghê “to decalre” (by means of speech), from vac- “to speak, say;” cf. Skt. vakti “speaks, says,” vacas- “word;”
Gk. epos “word;” L. vox “voice;” PIE base *wek- “to speak.”

If a force F acting on a body moves its point of application through a distance r, the work is defined by the product F.r.cosθ, where θ is the angle between the line of action of the force and the displacement. Work can be positive, negative, or zero.

Etymology (EN): M.E.; O.E. weorc, worc “something done, action, military fortification,” from P.Gmc. *werkan (cf. O.S., O.Fris., Du. werk, O.N. verk, O.H.G. werah, Ger. Werk), from PIE base *werg- “to work;” cognate with Pers. varz-, varzidan “to labor, practise,” → erg.

Etymology (PE): Kâr “work,” Mid.Pers kâr; Mod./Mid.Pers. kardan “to do, to work,” Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build,” Av. kərənaoiti “he makes;” cf. Skt. kr- “to do, to make,” krnoti “he makes, he does,”
karoti “he makes, he does,” karma “act, deed;” PIE base k^wer- “to do, to make.”

The least amount of energy required to remove an electron from the surface of a solid, to a point just outside the solid where the electron has zero kinetic energy. See also → photoelectric effect.

See also: → work; → function.

The → work of the resultant force exerted on a particle equals the change in kinetic energy of the particle.

See also: → work; → energy; → principle.

A group of people working together to achieve a stated goal.

See also: → work; → -ing; → group.

The double shock structure formed in any two fluids that collide supersonically. A working surface consists of two → shocks, a → bow shock where the ambient material is shocked and accelerated, and a jet shock or → Mach disk, where the → jet material is decelerated. It is common to find multiple working surfaces along the axis of an → Herbig-Haro jet, testifying to recurrent eruptions of the underlying source.

See also: → work; → -ing; → surface.

1. A place where manual work is done, especially manufacturing or repairing.
   

2. A group of people working on a creative project, discussing a topic, or studying a subject.

Etymology (EN): → work + shop M.E. shoppe, O.E. sceoppa;
cf. O.H.G. scopf “porch,” Ger. Schuppen “a shed”).

Etymology (PE): Kârgâh “workshop,” from kâr, → work, + gâh “place; time” (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”).

1. The Earth with its inhabitants. Compare → cosmos and → Universe.
   

2. Other planets, particularly → exoplanets.
   

3. Any realm, or domain, with all pertaining to it.
   

4. Physics: The → space-time in four dimensions, as distinguished from three-dimensional space. → world line.

Etymology (EN): M.E.; O.E. woruld, weorold; cf. O.S. werold, O.Fris. warld, Du. wereld, O.N. verold, O.H.G. weralt, Ger. Welt.

Etymology (PE): Jahân, variants keyhân, geyhân “world,” giti “world, material world, time;” Mid.Pers. gêhân “world,” gêtig “the material world; wordly,” Manichean Mid.Pers. gyh “world,” gyh’n “worlds;” Av. gaēθā- “being, world, matter, mankind” (O.Pers. gaiθā- “livestock”), gaya- “life, manner of living,” root gay- “to live” (present tense jiva-), cognate with Skt. jīv- “to live,” jīva- “alive, living;” Gk. bios “life,” L. vivus “living, alive,” vita “life;” PIE base *g^wei- “to live” (cf. O.E. cwic “alive;” O.C.S. zivo “to live;” Lith. gyvas “living, alive;” O.Ir. bethu “life,” bith “age, life, world;” Welsh byd “world”). The Pers. words zistan “to live,” zendé “alive,” zendegi “life,” and jân “vital spirit, soul; mind” belong to this family.

In relativity, the path traced out in four-dimensional → space-time that represents a continuous sequence of events relating to a given particle. A point on a world line is called an → event. Any straight world line corresponds to an → inertial motion. Curved world lines represent → accelerated motion. A world line that curves corresponds to an accelerated observer. World lines are shown on space-time diagrams.

See also: → world; → line.

A hypothetical topological feature, based on → general relativity, that connects two different points like a “tunnel” in → space-time.
The most common concept of a wormhole is an → Einstein-Rosen bridge. A trip through the wormhole could take much less time than a journey between the same starting and ending points in normal space. Wormholes have various types, intra-universe wormholes (connecting two distant regions of our Universe with each other) and inter-universe wormholes (that connect our Universe with another universe).

Etymology (EN): The term was coined by the Princeton physicist John Wheeler (1911-2008), from worm, M.E., O.E. wurm “serpent, dragon;” cf. O.S., O.H.G., Ger. wurm, O.Fris., Du. worm, Goth. waurms “serpent, worm;” akin to Pers. kerm “worm,” as below; → hole.

Etymology (PE): Kerm “worm;” Mid.Pers. kirm “worm, snake, dragon;” cf. Skt. krmi- “worm, maggot;” O.Ir. cruim “worm;” Lith. kirmis “worm;” L. vermis “worm;” E. worm, as above; surâx,
→ hole.

1a) Any building, structure, or thing reduced to a state of ruin.

1b) A vessel in a state of ruin from disaster at sea, on rocks, etc.

1c) The ruin or destruction of anything.

2. To cause the wreck of (Dictionary.com).

Etymology (EN): M.E. wrek, from Anglo-Norman wrek, from a Scandinavian source (Norwegian and Icelandic rek, Swedish vrak), from Proto-Germanic *wrekanan; cognate with E. wreak and wrack.

Etymology (PE): Kalin “wreck” has several variants in Iranian/Persian languages/dialects: (Lori) kalli, (Laki) kall “broken, damaged, wrecked;” (Malâyeri) kall “broken, damaged,” as in kuze-ye kall “damaged gugglet;” (Sâve-yi) kolul “damaged gugglet;” (Fin-e Bandar Abbas) cul “ruin;” (Xârestâni) kaleng “ruin, desolation;” (Dari-ye Yazd) xelak “ruin, wreck;” (Ossetic) xalyn, ixalun “to ruin, spoil.”

1. Act of wrecking; state of being wrecked.
   

   2. Remains or fragments of something that has been wrecked.

See also: → wreck + suffix -age forming mass and abstract nouns.

1. One that searches for or works on the wrecks of ships (as for rescue or for plunder).
   

   2. One that wrecks (Merriam-Webster.com).

See also: → wreck; → -er.

A low, sinuous tectonic ridge on a planetary surface that resembles a wrinkle in skin or cloth. These features were first detected on the Moon, but they have also been identified on other planetary bodies such as Mars, Mercury, and Venus.

Etymology (EN): M.E., back formation from wrinkled, from O.E. gewrinclod “wrinkled, crooked,” p.p. of gewrinclian “to wind, crease,” from perfective prefix ge- + -wrinclian “to wind;” → ridge

Etymology (PE): Ruk, → ridge; corukdâr, from coruk “wrinkle” + dâr “having, possessor” (from dâštan “to have, to possess,” Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maitain, keep in mind;” cf.
Skt. dhr-, dharma- “law;” Gk. thronos “elevated seat, throne;” L. firmus “firm, stable;” Lith. daryti “to make;” PIE *dher- “to hold, support”).

1. The carpus or lower part of the forearm where it joins the hand.
   

   2. The joint or articulation between the forearm and the hand (Dictionary.com).

Etymology (EN): M.E., O.E.; cognate with Ger. Rist “back of hand,” O.Norse rist “instep;” akin to writhe.

Etymology (PE): Moc “wrist,” related to mošt “fist;” Mid.Pers. mušt, must “fist;” Av. mušti- “fist;” cf. Skt. musti-, Pali mutthi-, L. manus (?).

To trace or form (letters, words, or other symbols) on a surface, typically paper, with a pen, pencil, or other similar instrument.

Etymology (EN): M.E. writen, O.E. writan “to score, outline, draw,” later “to set down in writing;” cf. O.Frisian writa “to write,” O.Saxon writan “to tear, scratch, write,” O.Norse rita “write, scratch,” O.H.G. rizan “to write, scratch, tear,” Ger. reissen “to tear, pull, sketch, draw.”

Etymology (PE): Neveštan, nevis- “to write,” variants Kurd. (Sor.) nus, nusen, Lori nisane “to write,” Kurd. (Kurm.) âvîtin, âvêntin, (Sor.) havîštin, hâvîtin “to compose (a song), to change (color);” Mid.Pers. (+ → ni-) nibištan, nebês- “to write,” pēsīdan “to adorn;” O.Pers. pais- “to cut, adorn, engrave;” Av. paēs- “to paint, adorn,” paēsa- “adornment;” cf. Skt. piśáti “adorns; cuts;” Gk. poikilos “multicolored;” L. pingit “embroiders, paints;” O.C.S. pisati “to write;” O.H.G. fēh “multicolored;” Lith. piēšti “to draw, adorn;” PIE base *peik- “colored, speckled.”

1. Not in accordance with what is morally right or good: a wrong deed.
   

2. Deviating from truth or fact; erroneous: a wrong answer.
   

3. Not correct in action, judgment, opinion, method, etc., as a person; in error (Dictionary.com).
   See also: → false, → invalid.

Etymology (EN): M.E. wrong, wrang, O.E. wrang “twisted, crooked,” from O.N. rangr “crooked, wry, wrong;” cf. Dan. vrang “crooked, wrong,” Du. wrang “sour, bitter.”

Etymology (PE): Nâdorost, from nâ- “not,” → a-, + dorost, → right.

The → determinant of order n associated with a set of n functions, in which the first row consists of the functions, the second row consists of the first → derivatives of the functions, the third row consists of their second derivatives, and so on. For example, If y₁ and y₂ are functions of x, the determinant W(y₁,y₂) = y₁ . y₂^’ - y₁^’ . y₂ is called the Wronskian of the given function.

See also: Named after the Polish mathematician Józef Hoene-Wroński (1776-1853).

The prototype of a subclass of → dwarf novae with an extremely long outburst period, comparable with that of a → recurrent nova.

See also: → variable star designation; → Sagittarius.