Globular Clusters Globular clusters are tightly gravitationally bound, being nearly spherical shaped. They typically contain many stars evolving off the lower main sequence to red giants. They are found spherically distributed around our galaxy, not in the plane. They look like little spherical fuzzy patches in small telescopes, an 8 inch can see stars. One of the brightest examples is the Hercules Cluster on an edge of the trapezoid in Hercules.
Many globular clusters are strong X-ray sources, perhaps from many neutron stars.
Measuring Distances to Clusters Parallax only works for the very nearest clusters, like the Hyades. Estimating the luminosity from the H-R diagram works, especially fitting the main sequence. Measuring the period of Cepheid variables gives luminosities for some globular clusters. Measuring the diameter of more distant globular clusters gives an estimates. One has to allow for the interstellar reddening from dust particles.