CIRCLES of Altitude

CIRCLES of Altitude, otherwise called almucantars, are circles parallel to the horizon, having their common pole in the zenith, and still diminishing as they approach the zenith. See ALMUCANTAR.

Diurnal Circles, are immovable circles, supposed to be described by the seven stars, and other points of the heavens, in their diurnal rotation round the earth; or rather, in the rotation of the earth round its axis. The diurnal circles are all unequal: the equator is the biggest.

Horary Circles, in Dialing, are the lines which show the hours on dials; though these be not drawn circular, but nearly straight. See DIALING.