They contain up to several thousand stars, but usually in the 100s, size of 30 lightyears but are irregular in shape. Visible now, fuzzy-looking patch of stars. Globular clusters are found mostly in the halo of our galaxy, but also in the disk. Much larger, can contain a million stars, highly condensed in the middle. Very symmetrical, spherical, 60-150 lightyears across.
All globular clusters look pretty much the same.
The difference between the front of the cluster and the back of the cluster is very small compared to the distance from the Earth. So we can compare apparent brightness of the stars in a cluster and won't have to worry about the difference in distance. The stars in a cluster all formed at the same time , or nearly the same time when compared to the age of the cluster itself. Therefore when we look at the stars, all the differences we see are due to the masses of the stars. By observing the motions of the stars in a nearby cluster over time, we can find the distance to the cluster.