North trails, the first astrophoto taken by many amateurs. It is amazing in its simplicity, yet always manages to astonish non-astronomers, who are fascinated by the beauty of this image.
The stars, seen as curved streaks around the central star, Polaris, do not move in reality. Instead, it is the Earth which turns around its own axis in 24 hours, once a day.
Polaris, also known as the Pole Star or Northern Star is almost directly "above" the north pole, meaning the Earth's axis points almost straight at it. Therefore, Polaris seems to stay in the same place while all of the other stars turn around it.
The star is easy to find: look for the Big Dipper, and take the two stars at the end of the "box". Follow their length about 7 times and you'll find another star in a region with relatively few bright stars. That's Polaris.
Its altitude above the horizon is always the same as your geographical latitude. So, for my home in Kronberg, Germany (8 degrees east longitude, 50 degrees north latitude), Polaris is always exactly 50 degrees above the horizon.
If you have ever tried to point a compass at Polaris, you'll notice that it doesn't always indicate north as the direction. This is because Polaris is above the Earth's real north pole, the one that the axis passes through. The magnetic north pole, the one that compasses point to, is several thousand miles away.
In addition to that, there are regional fluctuations in the geomagnetic field that throw off compasses by several degrees. A chart showing these fluctuations for the entire world is supplied with every good compasses.
You'll also notice that some stars pass directly under Polaris. These stars never set at this location, and are known as "circumpolar" (lat: around the pole).
Because the Pole Star's altitude is your latitude, the minimum declination of a star to be circumpolar is 90-<your latitude>. For 50 degrees latitude, a star has to have a declination of at least 40 degrees to be circumpolar.
Polaris cannot be seen from the southern hemisphere. However, observers there can point their cameras at the south celestial pole. But the SCP is not marked by a bright star. Therefore, southern hemisphere observers have a bit more problems aligning their telescopes with the earth's axis if they want to track objects across the sky.
