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

A catalog of 397 radio sources between declinations +20° and +27° which were compiled from a finding survey made at 635 MHz with the 64m radio telescope at the Australian National Radio Astronomy Observatory, Parkes, N.S.W. and published in 1968. Originally abbreviated PSR, this catalog, which is also called PKS, replaces and improves on four earlier lists (1964 to 1966).

Parkes, proper noun; selected, p.p. of → select; → region.

A → selection rule obeyed by → discrete transitions. Among them are: rigorous selection rules for → electric dipole transitions (→ permitted) requiring: 1) ΔJ must be 0 or ± 1 with J = 0 ↔ 0 forbidden. 2) ΔM_J = 0, ± 1. 3) → Parity change, i.e. even ↔ odd.

→ rigorous; → selection; → rule.

To choose from among several.

From L. selectus, p.p. of seligere "to choose out, gather apart," from se- "apart" + legere "to gather, select."

Gozidan "to select, choose;" Mid.Pers. vicitan, wizidan, wizin- "to choose, select, discriminate," related to cin-, cidan "to gather, collect;" Av. vicidāi- "to discern," viciθa- "separation, discernment;" from vi- "apart, away from" (O.Pers. viy- "apart, away;" cf. Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + kay- "to choose;" cf. Skt. ci- "to gather, heap up," cinoti "gathers."

Any of a set of rules specifying the relationships between the → quantum numbers that characterize the initial and final states of a quantum-mechanical system in a → discrete transition. Transitions that do not agree with the selection rules are called → forbidden and have considerably lower probability. There are several types of selection rules (→ rigorous selection rule, → LS coupling, etc.) for → electric dipole transition (→ permitted), → magnetic dipole (forbidden), electric → quadrupole (forbidden), etc.

Selection, verbal noun of → select; → rule.

Absorption which varies with the wavelength of radiation incident upon an absorbing substance.

Selective, verbal noun of → select; → absorption.

A type of scattering that occurs when certain → particles are more effective at scattering a particular → wavelength of light, as in → Rayleigh scattering.

→ selective; → scattering.

The process of choosing a site for an astronomical observatory based on meteorology, seeing conditions, and access to the site.

→ site; → selection.