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

An optical device, a modern version of the → Hartmann test, used for analyzing the wavefront of light. Theses sensors can be used to characterize the performance of optical systems. Moreover, they are increasingly used in real-time applications, such as → adaptive optics to remove the wavefront distortion before creating an image. It consists of a microlens array placed in front of a CCD array. A planar wavefront that is transmitted through a microlens array and imaged on the CCD array will form a regular pattern of bright spots. If, however, the wavefront is distorted, the light imaged on the CCD will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wavefront that was incident on the microlens array.

Named after the German astronomer Johannes Hartmann (1865-1936), who first developed the method, and R. V. Shack, who in the late 1960s replaced the screen by a microlens array; → wavefront; → sensor.

A wave that occurs in an elastic medium with the disturbances perpendicular to the direction of motion of the wave. Shear waves do not propagate through a fluid. Also called S-wave, secondary wave, and transverse wave.

→ shear; → wave.

A narrow region of abrupt, nearly discontinuous change in the physical characteristics of a medium in which the flow of a fluid changes from subsonic to supersonic. Across a shock wave there is always an extremely rapid rise in pressure, temperature, and density of the fluid.

→ shock; → wave.

A periodic oscillation that is defined by the function y = sin x.

→ sine; → wave.

A → longitudinal wave which when striking the ear gives rise to the sensation of sound. Such waves can be propagated in solids, liquids, and gases. The material particles transmitting sound waves oscillate in the direction of propagation of the wave itself. There is a large range of frequencies within which longitudinal waves can stimulate the human ear and brain to the sensation of hearing. This range is from about 20 → Hz to about 20,000 Hz and is called the audible range. → ultrasound; → infrasound.

→ sound; → wave.

An oscillation which alternatively assumes, for equal lengths of time, one or two fixed values.

→ square; → wave.

A wave produced by the simultaneous transmission of two similar wave motions in opposite directions. Same as stationary wave.

Standing verbal adjective from stand, cognate with Pers. istâdan, as below; → wave.

Istân pr.p. of istâdan "to stand;" Mid.Pers. êstâtan; O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" O.N. standa, Goth. standan, O.H.G. stantan, Swed. stå, Du. staan, Ger. stehen; O.E. standan; PIE base *sta- "to stand;" mowj, → wave.

Same as → standing wave.

→ stationary; → wave.

An electromagnetic wave having wavelengths less than one millimeter (frequencies greater than 300 gigahertz).

→ millimeter; → wave.

A wave in which the vibration or displacement takes place in a plane at right angles to the direction of propagation of the wave; e.g. electromagnetic radiation. → longitudinal wave.

→ transverse; → wave.

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.

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").

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.

→ 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.

→ 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.

→ 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.

→ wave; → mechanics

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

→ 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.

→ wave; → number

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

→ wave; → optics.

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

→ wave; packet from M.E. pak "bundle" + diminutive suffix -et; maybe from M.Fr. pacquet.

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.

→ wave; → plate.