Frank,
Celestia does not yet implement GlobularClusters.
They have to be faked by drawing Galaxy models.
Galaxy models are drawn only for Galaxy DSOs and are drawn when Galaxy rendering is enabled.
No model is drawn when OpenClusters are specified. They're location markers. Their contents are defined by Stars declared in stars.dat or in STC catalogs. There are lots of open clusters included in the Hipparcos database, although Celestia doesn't include DSC catalogs of their names. There are Addons available which define some of them. e.g. http://www.lepp.cornell.edu/~seb/celest ... usters.dsc
In principle one can create an STC file of a few thousand stars to simulate a globular cluster. Defining the stellar distributions properly can be a challenge.
Pseudo Globular Clusters
Re: Pseudo Globular Clusters
Selden