If you've ever wondered exactly how the sky moves at night, there may be no better way to understand than taking some completely stationary long exposure photos of the night sky.

In an span of free-time during an imaging session of M81 and M82, I did exactly that, setting up the trusty Olympus camera on a stationary tripod to get a cumulative look of the sky moving around the celestial north pole over the course of 75 minutes.  As can be seen, Polaris (the brightest streak in the image, appearing as a short line just left of center) is called the "North Star" for a good reason.  It sits conveniently close to the celestial north pole, though the actual difference between its position and the real north celestial pole is an important distinction astronomers and astrophotographers alike must make when aligning their mounts.  The equitorial mounts used to accurately track the sky are only as accurate as their polar alignment.  The closer the polar axis points to the north celestial pole (not Polaris!), the more accurately it tracks as the arms of the mount move around the pole with the night sky.

Star trails most certainly make for odd astrophotos, but a shot of northern night sky gives a pristine look at how the earth's rotation around its axis causes the sky to move in kind.