…continuedOpen Clusters by the Season
More Autumn Clusters
Just southwest of Beta (β) Cassiopeiae are two 5th magnitude stars, Sigma (σ) and Rho (ρ) Cassiopeiae, which are separated by a little less than 2°. Halfway between them is NGC 7789, an open cluster with about the same apparent diameter as that of the Moon.
NGC 7789 is one of those rare objects that is impressive in any size instrument. With a 4-inch rich-field telescope the cluster appears as a soft glow nearly ½° across and speckled with tiny, often elusive, individual stars. The 12-inch f/17 Porter turret telescope at Stellafane picks up more than 100 stars. Through a 16-inch aperture the view is spectacular, and the whole field is scattered with diamond dust. And a 22-inch Dobsonian reflector in the clear skies of California gave a most impressive view with countless sparkling points filling an entire 60x field.
Cassiopeia also contains the bright cluster M52, which lies between Cassiopeia and Cepheus on the edge of the dark lane in the Milky Way that divides these two constellations. M52 has a total magnitude of 6.9 and is visible in any finder. Recent studies indicate that this object is one of the richer and more compressed open clusters known. It's also relatively young, being some 20 million years old and comparable in age to the Pleiades.
Unlike some open clusters, M52 shows increasing richness with larger-aperture telescopes. Not large as galactic clusters go, it's 13' in diameter, but packed into that area are more than 150 stars of 11th magnitude and fainter. If it were not for its irregular outlines, M52 might well be mistaken for a globular cluster.