Deep-Sky Objects, Stars Twin stars Castor and Pollux, the 9–12 Geminorum Cluster, and the Eskimo Nebula
Deep-Sky Objects, Galaxies, Stars The extinct constellation Musca Borealis, open cluster Collinder 464, and spiral galaxy NGC 2403
Deep-Sky Objects, Stars The double star Alnitak, open cluster NGC 1817, and the Oyster Nebula (NGC 1501)
Stars What is the baseline for determining the magnitude scale of celestial objects? Why do brighter objects have negative numbers?
