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

The full width of a → profile (spectral line or a cross-cut in an image component) at half-maximum intensity.

→ full; → width; → half; → maximum.

Pahnâ, → width; nim, → half; bišiné, → maximum.

One of two equal or approximately equal parts of a divisible whole.

M.E., from O.E. h(e)alf "side, part," from P.Gmc. *khalbas "something divided" (cf. M.Du. half, Ger. halb, Goth. halbs "half").

Nim, nimé "half," from Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt.. néma- "half."

The moon when, at either quadrature, half its disk is illuminated.

→ half; → moon.

The length of time required for half of a given quantity of → radioactive material to → decay.

→ half; → life.

The angle between extreme points of the main lobe of an antenna pattern where the sensitivity of the antenna is half the value at the center of the lobe. This is the nominal resolving power of the antenna system.

→ half; → power; → beam; → width.

The thickness of material required to reduce the intensity of an → X-ray beam to one half of its initial value. The HVL is an indirect measure of the photon energies of a beam.

→ half; → value; → layer; → attenuation.

A plate of optical material whose thickness is such that the phase difference between the extraordinary and ordinary rays after passing through the place is exactly one-half cycle. It can serve to rotate the plane of polarization of a light beam.

→ half; → wave; → plate.