almucantar


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almucantar

(ˌælməˈkæntə) or

almacantar

n
1. (Astronomy) a circle on the celestial sphere parallel to the horizontal plane
2. an instrument for measuring altitudes
[C14: from French, from Arabic almukantarāt sundial]

almucantar

A circle on the celestial sphere that is parallel to the horizontal plane.
References in periodicals archive ?
In sky-scanning mode, 4STAR measures the diffuse sky radiance at prescribed scattering angles from the sun in the almucantar or principal plane to retrieve aerosol properties (single-scattering albedo, size distribution, and refractive index; see Kassianov et al.
I turned over my astrolabe, found Aldebaran on the clear plastic rete, and positioned the star at 41[degrees] in the east on the grid of almucantar circles.
deformation of local almucantar for astrolabes and similar instruments (Pesek, 1995);
This instrument is a multi-wavelength, automatic sun/sky radiometer that measures atmospheric spectral transmission and sky radiance in the almucantar (sky scanning at a constant zenithal angle) and principal plane (sky scanning at a constant azimuthal angle) using a combination of eight ion-assisted deposition interference filters: 1020, 870, 670, 500,440, 380, 340 for the aerosol channels and 940 nm for the water vapour of the total atmospheric column.