Deep Sky Objects - Star Clusters

Star clusters are groups of hundreds to hundreds of thousands stars that are gravitationally bound.  They are a class of deep sky objects (DSO).  There are two major types of star clusters, open clusters and globular clusters.  Globular clusters tend to have exponentially more stars than open clusters and tend to be rather old.  Open clusters,  on the other hand, tend to have only a few hundred stars and are relatively young.  Globular clusters are generally rather tight with a bright center.  Open clusters, on the other hand tend to spread out and thinner.  Sometimes they are spread out so that it can be difficult to fit it in the field of view, even in a 30mm eyepiece with a long focal length telescope.  Globular clusters are common features found in almost all galaxies.  In the Milky Way, there are an estimated 1,500 globulars. 

Star clusters are generally easy DSO's to locate in a telescope and often in binoculars. Some star clusters are even visible to the naked eye in dark skies.  Even in light polluted skies, most open clusters and many globular clusters are visible through a telescope.  Filters won't really do much for you when viewing these DSO's.  There are only two real exceptions.  A light pollution filter may be helpful on  globular clusters viewed in light polluted skies or a OIII filter for some nebulae that may surround a star cluster. 

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NGC 2808 Globular Cluster	Pleiades Cluster Open Cluster	M15 Globular Cluster
M80 Globular Cluster	NGC 346 Open Cluster with nebulosity

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