A circle on the celestial sphere parallel to the horizon; a parallel of altitude.
- ‘It can be programmed to collect data in manual or automated sequences of measurements, which include almucantar and principal plane scenarios.’
- ‘It does both principle-plane and almucantar sky-radiance scans, which are then processed through sophisticated inversion techniques.’
- ‘Once you have located the sun on the ecliptic, simply align the sun with the eastern horizon and read its position using the almucantars, which are drawn every ten degrees.’
- ‘To improve the accuracy of the scattering optical thickness, the inversion results are acceptable only if the radiance is measured across the total almucantar and is accurately fitted by a theoretical model.’
- ‘The circles are almacantars (loci of constant elevation), spaced at 10° intervals; radial distance is proportional to cos (elevation angle).’
2A telescope mounted on a float resting on mercury, used to determine stellar altitude and azimuth.
- ‘The pedestal of this almucantar is an ordinary cast-iron gaspipe, about 9 in. in diameter externally, and 6 ft. long, sunk 3 ft. in the ground.’
- ‘The discovery, in 1891, of the variation of latitude by Seth Carlo Chandler Jr. depended in part upon Chandler's invention of the almucantar.’
- ‘It had been invented by a professor at Harvard, but Howe's version of it was much more imposing; the almucantar at Harvard Observatory weighed 35 pounds -- Howe's, 2,300 pounds.’
Middle English from medieval Latin almucantarath or obsolete French almucantara, from Arabic al-muqanṭarāt ‘lines of celestial latitude’, based on al ‘the’ + qanṭara ‘arch’.