NGC 663

Caldwell 10, also known as NGC 663, is a prominent open cluster located in the constellation Cassiopeia. At a relatively young age of approximately 20 to 25 million years, this cluster provides a brilliant look at stellar youth, featuring a loose but striking grouping of stars that stand out clearly against the backdrop of the Milky Way. Its vibrant stellar population and clear structure make it an excellent reference for observers exploring the dynamic stellar neighborhoods within our own galaxy. This image was captured during the 2014 Advanced Observing Program at the Kitt Peak Visitor Center.

NGC 663 contains a notably high proportion of Be stars — rapidly rotating B-type stars surrounded by equatorial disks of ionized gas that emit strong spectral emission lines. This overabundance of Be stars compared to clusters of similar age has made NGC 663 a productive target for spectroscopic surveys studying the origins and evolution of stellar rotation. The cluster's integrated magnitude of approximately 7.1 makes it an easy binocular object, resolving into dozens of identifiable members in small telescopes. The richest section of the cluster presents a pleasing fan or arrowhead shape in the eyepiece.

Set against one of the densest stretches of the winter Milky Way in Cassiopeia, NGC 663 is often overlooked in favor of its more famous neighbor, the Double Cluster (Caldwell 14). But its own rich concentration of hot blue-white stars rewards exploration at low to moderate magnification, with intricate chains and groupings becoming apparent as the eye adjusts. At roughly 6,850 light-years from Earth, NGC 663 is one of the richer open clusters in this arm of the galaxy, containing an estimated 400 or more stellar members when faint stars are included.