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

An electric filter that transmits a known band of frequencies but suppresses unwanted frequencies above and below this band.

→ bandpass; → filter.

A type of narrow-band filter that uses the birefringence to produce selective absorption of polarized light.

→ birefringent; → filter.

Circular band-pass interference filter whose thickness and central wavelength vary along the perimeter. They are used in low-resolution spectrophotometers mainly in the infra-red.

→ circular; → variable; → filter.

Filter rejecting all light with wavelengths on one side of the cutoff wavelength.

→ cutoff; → filter.

An → interference filter used to selectively pass light of a small range of colors while reflecting other colors.

→ dichroism, → filter.

1) General: A device for separating the constituents of a system according to a physical property. In particular, a device for removing solid matter suspended in a liquid by forcing the suspension through a material which retains the solid matter while allowing the liquid to pass.
2) Optics: A device for transmitting electromagnetic radiation with restricted ranges of wavelength. Two types are generally used, → glass filters and → interference filters. See also → neutral density filter.
3) Electronics: A circuit or equipment allowing the transmission of desired frequencies and the elimination of others.

From M.L. filtrum "felt," which was used to strain impurities from liquid, from W.Gmc. *filtiz.

Pâlâyé, from pâlây present stem of pâludan "to filter, purify;" Mid.Pers. pâludan, pâlây- "to strain, filter, purify," from Proto-Iranian *pari-harz-, from prefix *pari- "around," → peri-, + harz- "to let go, release;" cf. Av. pairi.harəz- "to filter," from pairi- "around, over" (cf. Skt. pari; Gk. peri "around, about, beyond;" L. per "through;" PIE base *per- "through, across, beyond") + harəz- "to release" (especially water, liquid; cf. Chorasmian pžy- "to purify, filter;" Arm. (loanword) parzel "to filter, purify;"

A filter used in → broad-band photometry. The → bandwidth ranges usually between 30 and 100 nm.

→ glass; → filter.

A filter that uses the phenomenon of optical interferences between plane-parallel semi-transparent reflectors to transmit light selectively over a narrow wavelength band.

→ interference; → filter.

A type of narrow-band filter consisting of a series of birefringent crystals and polarizers invented by the French astronomer Bernard Lyot (1897-1952) for isolating and observing significant wavelengths of solar light.

→ Lyot division; → filter.

A filter having a flat response over the range of wavelengths of interest. Also called neutral filter or gray filter.

→ neutral; → density; → filter.

Same as → neutral density filter.

→ neutral; → filter.

A filter that polarizes light passing through it.

Polarizing, adj. of → polarize; → filter.