almucantar

noun2

1. •
   A small circle on the celestial sphere, parallel to the horizon, that is used in astronomy and navigation to show altitude of a star or any other heavenly body.

   • Almucantars, or parallels of altitude, are circles parallel to the horizon, or whose poles are the zenith and nadir. All the points of any one almucantar are at equal altitudes above the horizon. — 1816
2. •
   (no longer used, historical) An instrument for observing the heavenly bodies as they cross such a circle.