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

A variable → supergiant star with typical periods of the order of 10 to 100 days and amplitudes less than a few tenths of a magnitude. PVSGs are thought to be pulsating → g modes, caused by a density inversion, arising from an → opacity bump, most likely from Fe, H, and/or He.

→ periodical; → -ly; → variable; → supergiant.

A state or condition characterized by regular repetition in time or space.

→ periodic + → -ity.

A plot for examining frequency-domain data in an equi-spaced → time series. The periodogram is the → Fourier transform of the → autocovariance function. The periodogram method relies on the definition of the → power spectral density .

→ period; + euphonic infix -o-; → -gram.

Pertaining to, situated in, or constituting the periphery.

Adj. of → periphery.

In a charge-coupled device, the detection of charge collected by the transport register rather than by the image-sensing elements.

→ peripheral; → response.

In optics, the ability to see over large angles of view.

→ peripheral; → vision.

The external surface or boundary of a body. The circumference or perimeter of any closed figure.

From, M.E., from O.Fr. periferie, from L.L. peripheria, from Gk. peripheria "circumference, outer surface," literally "a carrying around," from peripheres "rounded, moving round," peripherein "to carry or move round," from → peri- "round about" + pherein "to carry;" cognate with Pers. bordan "to carry, lead," as below.

Pirâbar, from pirâ-, → peri-, + bar present stem of 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").

An optical instrument for viewing objects which are above the eye-level of the observer, or are placed so that direct vision is blocked.

→ peri-; + → -scope.

Layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C from a few to several thousands of years. It exists where summer heating fails to reach the base of the layer of frozen ground.

From perma(nent) + → frost.

Mândbašm, from mând, → permanent, + bašm, → frost.

Lasting or remaining without essential change.

Permanent, from M.Fr. permanent, from L. permanentem "remaining," pr.p. of permanere "endure, continue, stay to the end," from per- "through" + manere "stay," cognate with Pers. mândan, as below; → gas.

Gas which cannot be liquefied by pressure alone; gas above its critical temperature.

→ permanent; → gas.

A piece of magnetic material which, having been → magnetized, retains a substantial proportion of its → magnetization indefinitely. In permanent magnets the magnetic field is generated by the internal structure of the material itself. Atoms and crystals constituting materials are made up of electrons and atomic nuclei. Both the nucleus and the electrons themselves act like little magnets. There is also a magnetic field generated by the orbits of the electrons as they move about the nucleus. So the magnetic fields of permanent magnets are the sums of the nuclear spins, the electron spins and the orbits of the electrons themselves. In many materials, the magnetic fields are pointing in all sorts of random directions and cancel each other out and there is no permanent magnetism. But in certain materials, called → ferromagnets, all the spins and the orbits of the electrons will line up, causing the materials to become magnetic. Many permanent magnets are created by exposing the magnetic material to a very strong external magnetic field. Once the external magnetic field is removed, the treated magnetic material is now converted into a permanent magnet. Overheating a permanent magnet causes the magnet's atoms to vibrate violently and disrupt the alignment of the atomic domains and their dipoles. Once cooled, the domains will not realign as before on their own and will structurally become a temporary magnet (MagLab Dictionary).

→ permanent; → magnet.

Storage capacity which does not depend on a continuous supply of power, e.g. disks, magnetic tapes, etc.

→ permanent; → memory.

The degree of → magnetization of a material that responds linearly to an applied magnetic field. → magnetic permeability.

From permeable, from L. permeabilis "that can be passed through, passable," from L. permeare "to pass through," from per- "through" + meare "to pass," from PIE base *mei- "to change; to go, move."

Tarâvâyi quality noun of tarâvâ "permeable," from tarâvidan "to exude, trickle, ooze; to drop," probably from Proto-Iranian *tra-vaxš-. The first component *tra- "across, over, beyond," → trans-. The second component *vaxš-, cf. Av. uxš-/vaxš- "to sprinkle," present tense stem uxš-; cf. Skt. uks- "to sprinkle, moisten," uksati "spinkles, wets;" Gk. hygros "wet, moist, fluid;" L. uvidus "watery, humid, damp." Tarâvidan may be a back formation from *tarâvaš.

The act of permitting. Authorization granted to do something.

verbal noun of → permit; → -tion.

To allow to be done or occur.

From M.Fr. permetre, from L. permittere "give up, allow, allow to pass through," from per- "through;" (from PIE base *per- "through, across, beyond;" cf. Gk. peri "around, about, beyond;" O.Pers. pariy "around, about," Av. pairi "around, over;" Skt. pari; Indo-Iranian *pari- "around;" Mod.Pers. par-, pirâ- "around, about") + mittere "let go, send."

Parzâmidan, literally "to allow to go through," infinitive of parzâm, from par- "through," from O.Pers. pariy "around, about," Av. pairi "around, over," cognet with L. per-, as above + zâm stem of Mid.Pers. zâmenidan "to let go, lead, send," Mod.Pers. gâm "step, pace," âmadan "to come;" O.Pers./Av. gam- "to come; to go," Av. 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 base *gwem- "to go, come."

Allowed. → permitted line; → permitted transition.

Past participle of → permit.

An ordinary spectral line emitted by atoms undergoing energy transitions that are allowed by the selection rules of quantum mechanics. → forbidden lines.

→ permitted; → line.

A transition between two quantum mechanical states that does not violate the quantum mechanical selection rules.

→ permitted; → transition.

A measure of the ability of a material to transmit (or "permit") an electric field. Permittivity is defined as the ratio of the flux density produced by an electric field in a given dielectric to the flux density produced by that field in a vacuum. In → SI units, permittivity is measured in → farads per meter. The constant ε₀ is known as the permittivity of free space; its value is about 8.854 x 10^-12 F/m.

State or quality noun from → permit.