# Mass of the stellar cluster (not the whole galaxy)

Is there any general formula to determine the total mass of a cluster of stars?

I have searched for one in Google, but most of them are for calculating mass of binary stars or single stars using Kepler's law. If the total mass can be found by multiplying the mass of a star by total number of stars, then how can the average mass of an individual star and the total number of stars in a cluster system be calculated? Will the equation vary for cluster system? Assume that the cluster is observable and spectra are also attainable for the cluster.

• I think you have an interesting question here, but it needs some more information. Are you asking about an observed cluster? If so, can the individual stars be resolved in an image? Can their spectra be measured and many if not all of their radial velocities be independently determined? If so, that might make an answer easier, though I'm no expert so not 100% sure. But I am sure that you should add some more of this kind of detail to your question. Thanks! and welcome to Astronomy Stack Exchange!
– uhoh
May 14 at 2:11
• @uhoh yes, they are observable and their spectra can be determined.....how to do this calculation for a cluster then? will this vary for open and globular cluster? May 14 at 6:05
• Okay great, thanks! You should edit your question directly i.stack.imgur.com/dVpHK.png and add that in and any other details like those I've mentioned. There are already 2 close votes for "Needs details or clarity; This question should include more details and clarify the problem." and it takes 5 to close a question. i.stack.imgur.com/BpK4k.png Some people don't bother to read the comments unfortunately, clarifications should always be implemented in the post itself. Thanks!
– uhoh
May 14 at 6:30
• Can their proper motions be observed or 'just' their spectra and derived velocities? Can you provide / derive a velocity diagramme (wrt the centre of mass of the cluster)? Then you can derive the velocity dispersion. Will be interesting to see that plotted over central distance / radial distance on the (apparent) disc May 14 at 9:13
• @planetmaker will a HR diagram be ok? May 14 at 9:54