Almacantar

Almacantar, a name for circles of altitude parallel to the horizon, and hence for an astronomical instrument for determining time and latitude. The almacentar consists of a telescope revolving on a horizontal axis, which can be clamped at any altitude, the whole resting on a float sustained in a trough of mercury. The clamped telescope, when its floating support is turned, will therefore trace out a circle of equal altitude, and by the transits of stars across this circle, time and latitude can be obtained with very great accuracy. It can also be used for determining the apparent places of the heavenly bodies.