M3 Blinky-Blinky

This is amazing.
From Joel Hartman (Harvard-Smithsonian Center for Astrophysics): "RR Lyrae often have amplitudes of variation as high as 1 magnitude in V, and even higher in B. The RRab stars (fundamental mode pulsators) are the most numerous and have periods of roughly half a day. The RRc stars (first overtone pulsators) have periods of roughly a third of a day. What's more, because they are among the brightest stars in a globular cluster, they're actually very conspicous. If you were to watch them over the course of a night you would see quite a beautiful show, with the RR Lyrae blinking "on" and "off" like Christmas lights." (h/t APOD)