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

Philosophy of science: The concept according to which a proposition or theory cannot be scientific if it does not admit consideration of the possibility of its being false. According to Karl Popper (1902-1994), falsifiability is the crucial feature of scientific hypotheses. Any theory not falsifiable is said to be unscientific.

→ falsifiable; → -ity.

The quality of something that can be falsified. → falsifiability.

→ falsify; → -able.

1) To show or prove that a theory is incorrect or false.
2) To alter something in order to deceive.

Verb from → false.

The quality or condition of being → false. Opposite of → truth.

→ false; → -ity.

A group of entities with similar properties and common origin. → family of curves, → family of distributions, → family of sets, → comet family.

From L. familia "household, the slaves of a household," from famulus "servant," of unknown origin.

Xânevâdé "family," from xâné "house, home, houshold" + vâdé "root, foundation, origin." Xâné, from Mid.Pers. xânak, xân, xôn; cf. L. cunae "cradle;" Gk. kome "village;" Pers. Aftari dialect kiye "house, home;" PIE base *kei- "bed; to lie, to settle; beloved" (other cognates: P.Gmc. *khaim-; O.E. ham "dwelling, house, village;" E. home; Ger. Heim; L. civis "townsman;" Fr. cité; E. city; Skt. śiva- "auspicious, dear").

A set of similar curves which are distinguished by the values taken by one or more parameters in their general equation. For example, the general solution of a differential equation is represented by a family of curves.

→ family; → curve.

A set of distributions which have the same general mathematical → formula.

→ family; → distribution.

A → collection of → subsets of a set.

→ family; → set.

In 3D → magnetic reconnection models of solar plasma, a plane or curve surface composed of magnetic field lines emanating from the → magnetic null point (almost radially in the absence of electric currents and spirally if electric currents are present). See also → spine (Lau & Finn. 1990, ApJ 350, 672; Parnell et al. 1996, Physics of Plasmas 3, 759).

M.E., from O.E. fann, from L. vannus "a basket or shovel for winnowing grain," related to ventus, → wind.

Bâdzan "fan, ventilator," from bâd, → wind + zan from zadan "to strike, beat; to play an instrument; to do" (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- "to strike, hit, smite, kill" (jantar- "smiter"); cf. Skt. han- "to strike, beat" (hantar- "smiter, killer"); Gk. theinein "to strike;" L. fendere "to strike, push;" Gmc. *gundjo "war, battle;" PIE *g^when- "to strike, kill").

In the → Fanaroff-Riley classification, sources with R_FR < 0.5. Fanaroff and Riley (1974) found that nearly all sources with luminosity L(178MHz) ≤ 2 × 10²⁵h₁₀₀^-2 W Hz^-1 sr^-1 were of class I. FR-I → radio jets are thought to be → subsonic, possibly due to mass entrainment, which makes them amenable to distortions in the interaction with the ambient medium.

→ Fanaroff-Riley classification; → class.

In the → Fanaroff-Riley classification, → radio sources with hotspots in their lobes at distances from the center which are such that R_FR > 0.5. The → radio jets in FR-II sources are expected to be highly → supersonic, allowing them to travel large distances.

→ Fanaroff-Riley classification; → class.

A classification scheme for distinguishing a → radio galaxy from an → active galaxy based on their → radio frequency  and → luminosity and their kpc-scale appearance. Analyzing a sample of 57 radio galaxies from the → 3CR catalogue, which were clearly resolved at 1.4 GHz or 5 GHz, Fanaroff & Riley (1974) discovered that the relative positions of regions of high and low → surface brightness in the → lobes of extragalactic → radio sources are correlated with their radio luminosity. They divided the sample into two classes using the ratio R_FR of the distance between the regions of highest surface brightness on opposite sides of the central galaxy or quasar, to the total extent of the source up to the lowest brightness contour in the map. → Fanaroff-Riley Class I (FR-I) , → Fanaroff-Riley Class II (FR-II). The boundary between the two classes is not very sharp, and there is some overlap in the luminosities of sources classified as FR-I or FR-II on the basis of their structures. The physical cause of the FR-I/II dichotomy probably lies in the type of flow in the → radio jets.

Bernard L. Fanaroff and Julia M. Riley, 1974, MNRAS 167, 31P; → classification.

Being at a great distance; remote in time or place.

O.E. feorr "to a great distance, long ago," from P.Gmc. *ferro (cf. Du. ver, Ger. fern), from PIE *per- "through, across, beyond" (cf. O.Pers. para "on the other side (of);" Av. parə "beyond, more than, superior," parô "except," pərətu- "crossing, bridge;" Mod.Pers. pol "bridge;" Skt. parás "far, further, beyond," Gk. pera "across, beyond," L. per "through").

Dur, from Mid.Pers. dūr "far, distant, remote;" O.Pers. dūra- "far (in time or space)," dūraiy "afar, far away, far and wide;" Av. dūra-, dūirē "far," from dav- "to move away;" cf. Skt. dūrá- "far; distance (in space and time);" PIE base *deu- "to move forward, pass;" cf. Gk. den "for a long time," deros "lasting long."

Infrared radiation in the wavelength range (25-40) to (200-350) microns emitted by cold molecular/dust clouds.

→ far; → infrared.

Ultraviolet radiation in the wavelength range 912-2000 Å. See also → extreme ultraviolet.

→ far; → ultraviolet.

The portion of the → electromagnetic radiation in the wavelength range between about 30 and 300 → microns. See also: → infrared radiation, → near-infrared, → mid-infrared, → submillimeter radiation.

→ far; → infrared.

The → SI unit of → capacitance, defined as the capacitance of a conductor whose → potential increases by one → volt when a charge of 1 → coulomb is imparted to it; symbol F.

Named after the British physicist Michael Faraday (1791-1867), who made several major contributions to the fields of electricity and magnetism.

An enclosure made of conducting material, such as wire mesh or metal plates, that shields what it contains from external electric fields. According to → Gauss's theorem, the electric field inside a hollow conductor is nil. In order to demonstrate this, Faraday, in 1836, made a large box covered with wire mesh, and went inside it himself with an → electroscope. Powerful charges were applied to the outside of the box, but he detected no effect inside the cage.

→ farad; → cage.

Same as → Faraday rotation.

→ farad; → effect.

The rotation of the plane of → polarization experienced by a beam of → linearly polarized radiation when the radiation passes through a material containing a magnetic field with a component in the direction of propagation. This effect occurs in → H II regions in which a magnetic field causes a change in the polarized waves passing through. Same as → Faraday effect.

→ farad; → rotation.