1. The angle formed by the great circle running through two celestial objects and the hour circle running through one of the objects.

2. In measuring double stars, the angle formed between the great circle running through both components and the hour circle going through the primary measured from the north through the east from 0 to 360°.

That angle of the navigational triangle at the celestial body having the hour circle and the vertical circle at its sides. Also known as parallactic angle.