The Composition of Star Clusters

We had a wonderful speaker at the astronomy meeting last night.  She gave a fascinating, and very technical talk on "Gravitational Lensing."  It is a complicated subject and she did such a great  job of explaining all the ways distant objects could be "lensed" by objects of high mass located between us and the distant objects. Turns out that star clusters, because of their mass, can do gravitational lensing.  So because the speaker has a great sense of humor, she included this slide to explain what makes up the composition of a star cluster!  Very clever and it beats a plain old graph!