The following video is my first real attempt at time-lapse astrophotography. I chose one of my favorite constellations, Ursa Major (best known for containing The Big Dipper). The video shows the motion of the constellation over a 45-minute period.
I live in a small city, so some light pollution factored into the result but overall the night was quite clear. You can clearly make out “The Horse and Rider”, two stars that make up what is typically seen as the second star in The Big Dipper’s handle. The ability to see these two stars, Mizar and Alcor, was used by the Arabs, Romans, and English to test the eye-sight of their warriors.
But there’s even more to Mizar and Alcor than meets the (unaided) eye. Mizar is actually a quadruple system of two binary stars and Alcor is a binary system. Together, they make up sextuple system, as they are all apparently gravitationally bound.
To put it simply, Mizar — which we see as the brighter star, the horse, making up the Horse and Rider — is two sets of two stars orbiting each other. Alcor, is a single set of two stars orbiting each other, and is in turn interacting with the Mizar system. Six stars, dancing together in a cosmic folk dance, appearing to us on Earth as one or two stars (depending on your eyesight).
Additionally, this all goes to show that as much as we think we know about the cosmos, there is so much more out there to discover. Mizar and Alcor have been two of the most observed objects in the night sky for millennia, yet we still continue to unravel more of their magic.