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

Information transmitted by means of a modulated current or an electromagnetic wave and received by telephone, radio, television, etc.

→ electromagnetic; → signal.

The range of frequencies over which electromagnetic waves are propagated. → electromagnetic radiation.

→ electromagnetic; → spectrum.

The description of combined electric and magnetic fields mainly by → Maxwell's equations. Same as → electromagnetism.

→ electromagnetic; → theory.

The theory describing light as a wave phenomenon resulting from the combination of two electric and magnetic fields vibrating transversely and mutually at right angles. → electromagnetic radiation; → electromagnetic wave; → Maxwell's equations.

→ electromagnetic; → theory; → light.

A wave produced by oscillation or acceleration of an electric charge. → electromagnetic radiation.

→ electromagnetic; → wave.

1) The science dealing with the physical relations between → electricity and → magnetism. Same as → electromagnetic theory.
2) One of the four fundamental forces of nature, governing the electric and magnetic interaction between particles.

→ electro-; → magnetism.

The force, analogous to a pressure, which maintains a flow of electricity through a closed circuit. It is the algebraic sum of the → potential differences acting in the circuit. The unit of electromotive force is the → volt.

From → electro- + motive, from M.E., from M.Fr., from O.Fr. motif, from M.L. motivus "moving, impelling," from L. motus, p.p. of movere "to move," → motion; → force.

Niru, → force; barqrân, literally "driving electricity," from barq, → electro- + rân present stem of rândan, → drive.

The → elementary particle that possesses the smallest possible negative → electric charge. This structureless particle has an intrinsic → spin (1/2), a mass of 9.109 382 91 (40) x 10^-31 kg, and an electric charge of 1.602 176 565(35) × 10^-19 → coulombs, or 4.803 204 51(10) × 10^-10 → esu.

Term first suggested in 1891 by Irish physicist G. J. Stoney (1826-1911); from electr-, from → electric + -on, a suffix used in the names of subatomic particles, probably extracted from → ion.

The amount of energy released or absorbed in the process in which an electron is added to a neutral atom or molecule in gaseous state to form a negative ion.

→ electron; → affinity.

A process whereby an → unstable atom becomes stable. In this process, an → electron in an atom's inner shell is drawn into the → nucleus where it combines with a → proton, forming a → neutron and a → neutrino. The neutrino escapes from the atom's nucleus. The result is an element change, because the atom loses a proton. For example, an atom of → carbon (with 6 protons) becomes an atom of → boron (with 5 protons). Electron capture is also called K-capture since the captured electron usually comes from the atom's K-shell. See also → neutronization.

→ electron; → capture.

The charge of one electron, e = -1.602 176 × 10^-19→ coulombs or -4.803 204 51 × 10^-10→ statcoulombs.

→ electron; → charge.

Of an atom, a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels. The format consists of a series of numbers, letters and superscripts. For example, 1s² 2s² 2p³ means: 2 electrons in the 1s subshell, 2 electrons in the 2s subshell, and 3 electrons in the 2p subshell.

→ electron; → configuration.

A → degenerate matter in which electrons are very tightly packed together, as in a white dwarf, but cannot get closer than a certain limit to each other, because according to quantum mechanics laws (→ Pauli exclusion principle) the lowest energy levels can be occupied by only one electron. Therefore, electrons are forced into high energy states. And the significant pressure created by these high energy electrons supports white dwarf stars against their own gravity.

→ electron; → degeneracy.

The number of electrons per unit volume in an ionized medium, like an → H II region, as determined from → emission lines.

→ electron; → density.

A diffraction phenomenon resulting from the passage of electrons through matter, analogous to the diffraction of visible light. This phenomenon is the main evidence for the existence of waves associated with elementary particles; → de Broglie wavelength.

→ electron; → diffraction.

The mass of an electron, which is 9.109 382 91 × 10^-28 g.

→ electron; → mass.

The classical size of the electron given by r_e = e²/m_ec² = 2.81794 × 10^-13 cm, where e and m_e are the → electron charge and → electron mass, respectively, and c is the → speed of light.

→ electron; → radius.

Any of up to seven energy levels on which an electron may exist within an atom, the energies of the electrons on the same level being equal and on different levels being unequal. The number of electrons permitted in a shell is equal to 2n². A shell contains n² orbitals, and n subshells.

→ electron; → shell.

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.

→ electron-volt.

→ electron; → volt.