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

1) The act of visualizing (→ visualize).
2) The presentation of → information on a → screen.

Verbal noun of → visualize.

Cašm-did, Mid.Pers. cašm-did "visible," Mod.Pers. cašm-didâr by Tusi, in Pers. translation of Sufi's "Book of Fixed Stars," from cašm "eye" (Mid.Pers. cašm, Av. cašman- "eye," ākas- "to look," from prefix ā- + Proto-Iranian *kas- "to look, appear," cf. Skt. cáksus- "seeing") + did past stem of didan "to see" (Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").

The explosive ejection of superheated matter from a → volcano.

→ volcanic; → eruption.

Same as → common fraction.

M.E., from L. vulgaris, from vulgus "the common people," + -aris, → -ar.

→ common; → fraction.

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.

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

→ 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.

→ wavefront; → distortion.

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

→ weak; → emission; → line.

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

→ weak; → gravitational; → lensing.

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

→ weak; → interaction.

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

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

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.

→ weight; → concentration.

Same as → weight concentration.

→ weight; → fraction.

Same as → weight concentration.

→ weight; → fraction; → concentration.

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

→ western; → elongation.

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.

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

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.

→ white; → dwarf; → crystallization.

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.

→ Wilson effect; → depression.

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.

→ wind; → accretion.

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.

→ window; → function.