a N.E. direction, and terminates among mountains between Cassini and Calippus . I have seen this object easily with a 4 inch achromatic. Description: Wikipedia Theaetetus Additional Information Depth data from Kurt Fisher database Arthur, 1974: 2.83 km Westfall, 2000: 2.83 km Viscardy, 1985: 2.83 km Cherrington, 1969: 2.34 km Included