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How to Determine Latitude From Polaris

Polaris, also known as the North Star, is the one star that never changes its position in the night sky. Navigators have been using it to calculate their latitude on voyages for centuries. In an extreme disaster situation, or if your global positioning device malfunctions while you're on the open sea, it's useful to know your latitude. This trick is only for those living north of the equator, since the earth obstructs its view while south of it.

Things You'll Need

2 straight sticks, 2 feet in length
Level
Compass
Ruler
Marker
Scientific calculator

Instructions

- 1
  Drive a straight stick into the ground, and use a level to straighten it upright. Use the level on four sides of the stick, and adjust its angle to the ground as necessary.
- 2
  Find the southward direction from the stick with a compass and drive a second stick into the ground about a foot south of the first stick. Straighten it in the same fashion as the first one. The height of the sticks should be exactly the same.
- 3
  Locate Polaris once the sky darkens after sunset. You can find it by tracing a line upwards from the two stars of the Big Dipper that form the edge of the "cup" until you find a star significantly brighter than the surrounding stars. This star is Polaris.
- 4
  Crouch down next to the southern stick and align your eye so that the top of the northern stick is in line with Polaris. Mark the height of your eye on the southern stick.
- 5
  Measure the distance between the sticks, and the distance from the marked height to the top of the southern stick. Use a scientific calculator to evaluate the inverse tangent of the ratio of the height to the distance between the sticks (the inverse tangent button is labeled "tan¯¹" on the scientific calculator). Type the height of the resulting right triangle divided by the adjacent arm of the angle. The result, in degrees, is your latitude north of the equator.

Astronomy