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

1) A belief or judgment that rests on grounds insufficient to produce complete certainty.
2) A personal view, attitude, or appraisal.
3) Law: The formal statement by a judge or court of the reasoning and the principles of law used in reaching a decision of a case (Dictionary.com).

M.E., from O.Fr., from L. opinion- "opinion, conjecture; appreciation," from opinari "to think, judge, suppose," from PIE *op- "to choose."

Pažân, from Pashto pažân / pêžân, from prefix- pa-, originally *pati-, + žân variant of Pers. dân-, dânestan "to know," zân as in farzâne "intelligent, wise;" Balochi zân, Kurd. zân "to know;" cf. Sogd. patzân, Khotanese paysân- "to know;" Yidgha and Munji vəzân "to know;" Yizghulami vəzan, Yaghnobi bīzon, Sarigholi pajan, Ormuri pazán "to know;" Av. paiti-zan- "to recognize, acknowledge, appreciate;" from prefix paiti- + zan- "to know, have knowledge;" Mod.Pers. dân-, dânestan "to know," variant šenâxtan "to know, recognize," → science.

A process in which light energy is used to raise electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction, to pump the active laser medium so as to achieve population inversion. The technique was developed by 1966 Nobel Prize winner Alfred Kastler in the early 1950's.

→ optical; → pumping.

The condition of a system in which the damping is so large that the system comes to a position of rest without oscillating.

→ over-; → damping.

An act or instance related to → overlap.

Verbal noun of → overlap.

The component of a → planispheric astrolabe that is inserted in the back of the → mater. The pin enables the main parts of the instrument (the → alidade, the → rete, and the → rule) to rotate freely around the common center of the mater and the → tympanum (online museo galileo, VirtualMuseum).

M.E. pinne, from O.E. pinn "peg, bolt," from L. pinna "a feather, plume."

Âsé, → axis.

The constriction of a current-carrying plasma column caused by its external self-magnetic field.

M.E. pinch, from O.Fr. pincier "to pinch," possibly from V.L. *punctiare "to pierce," from L. punctum "point," and *piccare "to pierce."

Penk "pinch, squeezing or compressing between the finger and thumb" (Dehxodâ), cf. (Tabari) pendik, pecelik, (Kermâni) perenju "pinch," maybe related to panjé "the palm of the hand with five fingers; fist," from panj "five," from Mid.Pers. panj; Av. panca; cf. Skt. pánca; Gk. pente; L. quinque; O.E. fif, from P.Gmc. *fimfe (O.S. fif, O.H.G. funf); from PIE base *penk^we "five."

An → aberration of a → lens  → system in which → magnification increases with → distance from the → optical axis, whereby → horizontal and → vertical lines bend inward toward the → center of the → field. Opposite of → barrel distortion.

Pincushion, from pin, from M.E. pinne, O.E. pinn "peg;" cf. D. pin, Ger. Pinne; perhaps from L. pinna "feather, quill" + cushion, M.E. cuisshin, O.Fr. coissin (Fr. coussin) a variant of V.L. *coxinum, either from L. coxa "hip, thigh," or from L. culcita "mattress;" → distortion.

Cowlegi, → distortion; bâleštaki, adj. of bâleštak, diminutive of bâlešt, variant bâleš "cushion, pillow," Mid.Pers. bâlišn, bâlên "cushion, pillow;" Av. barəiš- "pillow, cushion;" cf. Skt. barhis- "straw, a bed or layer of kusa grass strewed over the sacrificial ground."

In a → planispheric astrolabe, a vane on an end of an → alidade with a hole, slot, or other indicator through which one can view a distant object. There may also be a pointer or pointers on the alidade to indicate a position on a scale.

Diminutive of L. pinna "feather, wing, fin;" + → -ule.

Mori (Biruni).

A child's toy consisting of a wheel or leaflike curls of paper or plastic loosely attached by a pin to a stick, designed to revolve when blown by or as by the wind (Dictionary.com).

→ pin; → wheel.

Ferferé "pinwheel," of unknown origin.

The collective opinion of many people on some issue, problem, etc., especially as a guide to action, decision, or the like (Dictionary.com).

→ public; → opinion.

The act or process of pumping. → optical pumping.

Verbal noun of → pump.

Damping of a system which loses energy by → electromagnetic radiation.

→ radiation; → damping.

A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 10⁷ K) and tenuous (~ 10^-4 cm^-3) gas (several 10¹³ → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).

→ ram; → pressure; → strip.

The change in the direction of the → rotation axis of a → pulsar in a → binary pulsar. In such a system, → geodetic precession leads to a relativistic → spin-orbit coupling, analogous of → spin-orbit coupling in atomic physics. In consequence, the pulsar spin precesses about the total → angular momentum, changing the relative → orientation of the pulsar toward Earth (Damour & Ruffini, 1974). As a result, the angle between the pulsar → rotation axis and our → line of sight changes with time, so that different portions of the emission beam can be observed leading to changes in the measured pulse profile. In extreme cases, the precession may even move the beam out of our line of sight and the pulsar may disappear as predicted for PSR 1913+16 for the year 2025.

→ relativistic; → spin; → precession.

The smoothing of primordial → density fluctuations at high frequencies caused by photon → diffusion. Before the → decoupling era, photons and → baryons were tightly coupled to each other by → Compton scattering. However, the transition to a transparent → Universe was not instantaneous. As the → opacity of the Universe dropped, the photons started diffusing away from the positions they had while opaque, hence undergoing a → random walk. Since the → acoustic waves in the decoupling era were driven by photon pressure, the photon diffusion also led to damping of the → baryon acoustic oscillations. Silk damping suppresses all perturbations with masses smaller than about 10¹³ Msun. The implication for a theory of → structure formation is that individual galaxies must have formed in a → top-down structure formation mechanism, i.e. by the fragmentation of larger objects. However, in theories of structure formation which include → non-baryonic dark matter galaxies can form from smaller objects in a → bottom-up scenario.

Joseph Silk (1942-); → damping.

1) Mechanics: The rotation of a body about an axis through the body. To cause to turn around rapidly, as on an axis. To revolve or rotate rapidly,
2) Quantum mechanics: See → spin quantum number; → spin angular momentum.

M.E. spinnen; O.E. spinnan "to draw out and twist fibers into thread" (cf. O.N., O.Fris. spinna, Dan. spinde, Du. spinnen, O.H.G. spinnan, Ger. spinnen); cognate with Pers. tan-, tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare," Latv. tikls "net;" PIE base *ten- "to stretch").

Espin, loan from E., as above.

An intrinsic quantum mechanical characteristic of a particle that has no classical counterpart but may loosely be likened to the classical → angular momentum of a particle arising from rotation about its own axis. The magnitude of spin angular momentum is given by the expression S = ħ √ s(s + 1), where s is the → spin quantum number. As an example, the spin of an electron is s = 1/2; this means that its spin angular momentum is (ħ /2) √ 3 or 0.91 x 10^-34 J.s. In addition, the projection of an angular momentum onto some defined axis is also quantized, with a z-component S_z = m_sħ. The only values of m_s (magnetic quantum number) are ± 1/2. See also → Stern-Gerlach experiment.

→ spin; → angular; → momentum.

The magnetic moment associated with the → spin angular momentum of a charged particle. The direction of the magnetic moment is opposite to the direction of the angular momentum. The magnitude of the magnetic moment is given by: μ = -g(q / 2m)J, where q is the charge, m is the mass, and J the angular momentum. The parameter g is a characteristic of the state of the atom. It would be 1 for a pure orbital moment, or 2 for a spin moment, or some other number in between for a complicated system like an atom. The quantity in the parenthesis for the electron is the → Bohr magneton. The electron spin magnetic moment is important in the → spin-orbit interaction which splits atomic energy levels and gives rise to → fine structure in the spectra of atoms. It is also a factor in the interaction of atom with external fields, → Zeeman effect.

→ spin; → magnetic moment.

An integer or half-integer on which the magnitude of a particle's → spin angular momentum depends. It is expressed in units of → Planck's constant divided by 2π. Called also spin, denoted s. The spin of a particle can only have a value that is zero or a multiple of 1/2. Particles with half-integer spins, 1/2, 3/2, 5/2, ..., are → fermions. Particles with integer spin (0, 1, 2, ...) are called → bosons.

→ spin; → quantum; → number.

The → excitation temperature of the → hyperfine structure levels of the → neutral hydrogen→ 21-centimeter line.

→ spin; → temperature.