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

Tending or serving to disperse.

From → disperse + → -ive.

The reciprocal of the → dispersive power.

→ dispersive; → index.

A medium in which the → phase velocity is a function of → wave number (→ frequency).

→ dispersive; → medium.

A measure of the ability of a medium to separate different colors of light. It is defined by: (n₂ - n₁)/(n - 1), where  n₁ and n₂ are refractive indices at two specified widely differing wavelengths, and n is the → index of refraction for the average of these wavelengths.

→ dispersive; → power.

An experiment of → diffraction and → interference of two light beams using a → double slit; → Young's experiment.

→ double; → slit; → experiment.

The outcome of a → merger process between two galaxies, each with its own central → supermassive black hole (SMBH), resulting in a remnant galaxy hosting two SMBHs. Simulations of → galaxy mergers show there should be lots of dual → active galactic nuclei (AGN) visible at less than 10 kpc separations. As of 2015 more than 100 known dual supermassive black holes have been found. See also → binary supermassive black hole.

→ dual; → supermassive; → black; → hole.

An indication of the heat amount received by → dust grains from the ambient → radiation field. Dust temperature depends on the optical properties and → sizes of grains (i.e., on the way they → absorb and → emit radiation) as well as on the → interstellar radiation field. Most of the visible and → ultraviolet radiation in galaxies from stars passes through clouds of particles and heats them. This heating leads to re-radiation at much longer wavelengths extending to the millimeter.

→ dust; → temperature.

A person or thing that secretly listens to or monitors the private conversation or data of others.

From M.E. eavesdrop, from O.E. yfesdrype "place around a house where the rainwater drips off the roof," literally "one who stands on the eavesdrop in order to listen to conversations inside the house," from eaves "the lower border of a roof that overhangs the wall" + drip, drop "to fall in small portions."

Gušâr in Tabari "eavesdropper," from guš, → ear, + -âr probably contraction of dâr (as in dustâr/dustdâr) agent noun from dâštan "to hold, have, possess; appoint, erect," → property.

Of an antenna, the ratio of the extracted power by the antenna to the power per unit area (power density) in the incident wave.

→ effective; → aperture.

A measure of the surface temperature of a star derived from the total emitted energy, assuming that the star is a → blackbody emitter (→ Stefan-Boltzmann law, → Planck's radiation law). See also → brightness temperature; → color temperature.

→ effective; → temperature.

A characteristic parameter occurring in the → Einstein model of → specific heats.

→ Einstein; → temperature.

1) The temperature of electrons in an interstellar ionized nebula (e.g. in → H II regions and → planetary nebulae) as determined by characteristic → emission lines (optical → forbidden lines or → radio recombination lines).
2) In the → solar wind, the temperature derived from the mean → thermal agitation of the electrons. More specifically, electric field receivers on board space probes carry out the spectroscopy of the → thermal noise due to the potential fluctuations produced by the thermal agitation of the electrons, yielding the electron temperature in certain conditions (N. Meyer-Vernet, 2007, Basics of the Solar Wind, Cambridge Univ. Press). See also → proton temperature.

→ electron; → temperature.

A monarch who rules or reigns over an empire.

M.E., from O.Fr. empereor "emperor, leader, ruler," from L. imperiatorem (nominative imperiator) "commander, emperor," from p.p. stem of → imperare "to command."

Parmâtyâr, from parmât, present stem of parmâtidan, → imperare, + suffix -yâr, as in šahryâr "sovereign, king," hušyâr "sober, cautious, intelligent," kušyâr "name of a physician; industrious" kâmyâr "happy, powerful," and baxtyâr "fortunate, rich."

Of a gas or plasma, the temperature deduced from the → populations of atomic → excited states, as expressed by the Boltzmann formula: N_u/N_l = (g_u/g_l) exp (-ΔE/kT_ex), where N_u and N_l are the upper level and lower level populations respectively, g_u and g_l the statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h→ Planck's constant. The higher the energy of the occupied states, the higher the excitation temperature.

→ excitation; → temperature.

An act or operation for the purpose of discovering something unknown or of testing a principle, supposition. See: → Aspect experiment, → Carnal-Mlynek experiment, → Davisson-Germer experiment, → double-slit experiment, → Eratosthenes experiment, → Hafele-Keating experiment, → Hertz experiment, → Michelson-Morley experiment, → Millikan's oil-drop experiment, → Pascal's barrel experiment, → random experiment, → Stern-Gerlach experiment, → thought experiment, → toothed-wheel experiment, → Trouton-Noble experiment, → Young's experiment.

From O.Fr. experiment, from L. experimentum "a trial, test," from experiri "to test, try," from → ex- "out of" + peritus "experienced, tested."

Âzmâyeš, verbal noun of âzmudan, âzmây- "to try, experiment, test;" Mid.Pers. uzmudan, ôzmutan "to test, try, prove;" from O.Pers./Av. *uz-māy-, from uz-, → ex- + mā(y)- "to measure," Proto-Ir. *maH- "to measure;" PIE *meH- "to measure;" cf. Skt. mati "measures," matra "measure;" Gk. metra "lot, portion;" L. metri "to measure."

A type of interferometer wherein the beam of light undergoes multiple reflections between two closely spaced partially silvered surfaces. Part of the light is transmitted each time the light reaches the second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like the multiple slits of a diffraction grating increase its resolution.

The design was conceived by French physicists Charles Fabry (1867-1945) and Alfred Pérot (1863-1925) in the late nineteenth century; → interferometer.

The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.

→ five; → hundred; → meter; → aperture; → spherical; → radio; → telescope.

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

→ four; → dimensional; → operator.

Same as → perigee full Moon.

→ full; → super-; → Moon.

An experiment performed in 1971 using four atomic → cesium clocks transported in jet airplanes eastward and westward around the Earth to verify the → time dilation predicted by the theory of → special relativity.

J.C. Hafele and R. E. Keating, 1972, Science 177, 166; → experiment.