Open clusters, also known as Galactic Clusters, are ubiquitous along the disk of our Milky Way Galaxy, and therefore other spiral galaxies as well. There is an endless variety of shapes, sizes, densities, and star population among the class of object. There are dozens of attractive examples, and seemingly countless non-descript examples one could view, depending on the aperture of your telescope.
Perhaps the most well known is The Pleiades cluster in Taurus, known since antiquity. The Beehive appears naked-eye as a small cloud in the constellation Cancer, under sufficiently dark conditions. One you may not be aware of is NGC 7789, known as Caroline's Rose in Cassiopeia. You'll find it easily hopping from (P) Polaris, our north star to (B) Beta Cass then west to the gently arcing trio of Tau, Rho and Sigma Cas, as shown in this chart with a five degree (finderscope) inset:
NGC 7789 sites almost directly between magnitudes 4.87 Sigma and 4.50 Rho. At a bright magnitude 6.70 this cluster is as large as the largest biggest northern globular clusters, subtending an apparent 16 arc-minutes. It should be a binocular target, but use a telescope to discover the sheer beauty it displays. It is truly among the best in class and bright enough to be enjoyed even in suburban skies!
In a telescope you'll find many dozens of stars, evenly distributed and quite uniform in magnitude, as shown in this excellent representation by Mikael Anderlund:
The intricacy and density of this view may be paralleled only by Messier 37 in Auriga, making this a hidden gem.
Here are two observations by Steve Gottlieb, and a wikisky.org image to whet your appetite:
- 17.5" (10/12/85): a few hundred stars were resolved in a 20' field. Remarkably rich and fairly uniform carpet of stars mag 11 and fainter.
- 8" (11/8/80): extremely rich, uniform in faint stars. Certainly among the top open clusters with this aperture.
Why is it named Caroline's Rose? The swirling pattern, replete with dark curving channels, is thought to look like the swirling pattern of rose petals as seen from above. And Caroline, none other than the famous female Herschel, sister and partner of William, quite a dynamic astronomical pair! Caroline's outstanding contributions to astronomy are among the lasting examples by the famous women in this science, including Annie Jump Cannon, Williamina Flemming and others. If you have a daughter interested in enjoyment of the night skies, show her this object, and point her at the famous women who may illuminate her way.
