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

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

→ wavefront; → correction.

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

→ waxing; → crescent.

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.

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

→ well; → order; → set.

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.

→ wide field; → infrared; → survey; → explorer.

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.

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.

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 slender flexible thread or rod of metal.

M.E., O.E. wir, cf. O.N. viravirka "filigree work," Swed. vira "to twist," O.H.G. wiara "fine gold work."

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.

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.

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

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).

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.

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.

→ 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).

→ wreck; → -er.

A region of → molecular clouds whose chemistry is affected by → X-rays from neighboring sources.

→ X-ray; → dissociation; → region.

The largest → refracting telescope and the last of the great refractors with a lens diameter of 102 cm (f/d = 19), completed in 1897. The lens was ground by American telescope builders Alvan Clark & Sons. Used mainly for both visual and photographic studies of double stars, it is typical of the long-tube refractors traditionally employed in such work.

After Yerkes Observatory; → refractor.

The removal of non-significant zeroes from a number. For example, replacing 531.2300 by 531.23.

→ zero; → suppression.