Sorry for the big picture file, but it’s worth it.
This is today’s Astronomy Picture of the Day, an image of the globular cluster M3 taken by Joel Hartman and Krzysztof Stanek at the Harvard-Smithsonian Center for Astrophysics. Take the time to let it fully load; it’s not just a still picture, but a short movie that shows the “twinkling” of variable stars in the cluster. (Details here.)
Globular clusters are bound systems of very old stars, orbiting around (and often passing through) the main disk of our galaxy. The variable stars in the above image are RR Lyrae variables, single stars that pulsate with periods of about half a day. This is a highly sped-up view, compressing images taken over the course of a single night into a few seconds. Fun to look at, but also a sign of the times: astronomers are increasingly using modern technology to extend wide-field imaging from static images into the time domain.
If you like the twinkling stars, check out movies of motions in the center of our galaxy, showing stars moving rapidly around a heavy, invisible mass — in fact, a million-solar-mass black hole.