Diameters are given either as the visually observed size or some theoretical one. Telescopic diameters are often expressed in arc minutes, whose outliers make any true estimation difficult. Perhaps a better definition of the outer edges would be based on the gravitational attraction of all the stars just being sufficient enough to hold individuals from escaping.
In true diameter, a globular could extend as far as roughly 500pc., though the larger ones like Omega Centauri visually appears to extends up to 300pc. On the other end of the scale, some GSC's maybe as little as 5pc.
The average, as far as I know, is about 50 parsecs or so.
I'll post a better answer when I find some old references I have!!
Last edited by Enchilada; 02-07-2009 at 03:17 AM.
Reason: fixed figures
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