High Quality Content by WIKIPEDIA articles! NGC 663, also known as Caldwell 10, is young open cluster of about 400 stars in the Cassiopeia constellation. It has an estimated 400 stars and spans about a quarter of a degree across the sky. It can reportedly be detected with the unaided eye, although a telescope is recommended for best viewing. The brightest members of the cluster can be viewed with binoculars. Although the listed visual magnitude is 7.1, several observers have reported higher estimates.