Open Clusters in Cassiopeia
The area of sky surrounding the "W" shape of Cassiopeia is filled with numerous open clusters that can be seen and appreciated using even the smallest of telescopes. This wide-field view shows three of them. The triangular cluster to the lower right is Messier 103. The larger cluster to the upper left is NGC 663, also known as Caldwell 10. Finally, below NGC 663 is a smaller and more compact cluster, NGC 659.
These three clusters are thought to be part of a larger group called the Cassiopeia OB8 association. OB associations are loose groupings of very large and hot blue-white stars of spectral classes O and B. These giant stars burn brightly during their comparatively short stellar lives (lasting for millions rather than billions of years).
Image details: Exposure times of 15 minutes luminance and 10 minutes each of red, green and blue, taken with an SBIG ST-8300M imager and a 500 mm Tokina lens.