First, we'll cross our fingers that this nameless desert is in the Northern Hemisphere. You can certainly navigate without the North Star; but having a single, bright, easily identifiable light that never "moves" and sits precisely above true north is a significant asset.
The North Star, or Polaris, is a fixed point. It sits above the North Pole, aligned precisely with Earth's axis of rotation, so unlike every other star in the sky its apparent location never changes [source: Gooley]. Once you find the North Star, which is pretty easy to do, you need only draw a line directly down to the horizon to find true north.
Two star groupings point the way to the North Star: the Big Dipper, aka the Plough (in the constellation Ursa Major) and Cassiopeia. Throughout out most of the Northern Hemisphere, neither one ever "sets," or dips below the horizon, so they're reliable indicators at any time of night [source: VanHaren].
The North Star lies about midway between these star groups; either can lead you to it. The Big Dipper is easier to use, though, because of the alignment of its stars.
The Big Dipper comprises seven bright stars that form the shape of a ladle (or dipper). The most important stars are the two that mark the outside edge of the scoop, farthest from the tip of the handle. These are the pointer stars: If you draw an imaginary line from the bottom-edge star to the top-edge star and extend the line about five times the distance between the pointers, you smack right into the recognizably bright North Star [source: Gooley].
Sitting on the other side of the North Star is Cassiopeia, whose five stars mark the five points of the letter W." The center star is the pointer. If you draw a line from that star in the direction of the W's top points, at 90-degree angles from each of the bottom points, the first bright star your line touches is Polaris.
Once you know Polaris, you know north. Turn 90 degrees clockwise to go east, another 90 to go south, and a final 90 to head west.
The North Star's location above true north makes establishing directions rather simple, but direction only gets you so far. For it to help you get home, you need to know which way home is. If, for example, your boat sinks, and you know the nearest land is a few hundred miles east, then you can head your raft in an easterly direction.
But what if you're in the Southern Hemisphere? There's no "South Star" to guide you, but there's something close to it.