How to Use the Stars to Find Your Way

By: Julia Layton

Finding Latitude: Use Your Hands

Both polar (or, in the South, near-polar) locations can be used to find latitude, which indicates one's north/south distance from the (east/west-running) equator. Latitude is measured in degrees, referencing the 360 degrees that is the entire Earth.

Together with longitude, which measures east/west distance from the (north/south-running) prime meridian, latitude can tell you where you are on the planet, even if all you can see is sandy desert.


Actually, for latitude, you need to see two more things: a polar star and the horizon. Inconveniently, there are only two times in any 24-hour period when you can see both: the moment before the sun sets and the moment before the sun rises. Twilight.

To determine latitude in the short windows of twilight, you need to find the angle of elevation of a polar star. This calculation requires three points of reference: a polar star, a horizon and you. Once you have these three points, you'll draw two lines – one from you to the star, and one from you to the horizon. The angle formed at the intersection of these lines is your latitude.

At the North Pole, where the North Star is directly overhead, the latitude is 90 degrees north; at the South Pole, it's 90 degrees south; and at the equator, where the polar stars are on the horizon, latitude is 0 degrees.

There are manual tools that make the calculation easier, and more accurate. The sextant is probably the most well-known. Invented in the 1700s, it uses mirrors and a moveable arm to line up any two objects and determine the angle between them [source: Beyond the Map]. And yet, without a sextant, without even sticks, you can still get a pretty good fix on it.

At twilight, find the polar star, let's say the North Star, and the horizon, and draw an imaginary line connecting them. Extend your arm toward the horizon, and make a fist. Your knuckles should be facing outward. Then, fist over fist, count how many of your fists it takes to get from the horizon to the North Star. Each fist-length measures approximately 10 degrees. Let's say it takes three fists. You now know your latitude is around 30 degrees N.

Latitude, of course, is only half the positional equation. It's nice to know your desert is 30 degrees north of the equator, but the equator circles the entire planet.

You need longitude, too. And longitude is tricky.