Starship Asterisk*

I remember reading somewhere that we cannot discern individual stars within galaxies such as M31 and M33 even with our most powerful visual telescopes including the Hubble. Is that true? If it is then what I think are individual stars within a frame of M31 are either foreground stars within the MilkyWay or are star clusters within the distant galaxies.

Jim

No thats not true, we can pick out stars in the local group fairly easily even with ground based telescopes. Using the HST we can resolve stars as far away as about 10Mpc, though these tend to be only the very brightest stars.

Here is a nice paper that shows how it is done. Warning technical.

http://arxiv.org/pdf/astro-ph/0505622


In general wherever you look most of the objects will tend to be stars within the MW, though some of the objects you describe probably are globular clusters or massive young clusters in the external galaxies, some may even be stars in the galaxies.