The Challenge: Measure Latitude and Longitude Page: 1 2 3 4 5 6 7 8 9 10

Using the North Star to Measure Latitude

Once you've found the North Star it's simple to determine your latitude.

How to locate the North Star

1. First, locate the Big Dipper, Ursa Major (called The Plough in the U.K.).

2. Find the two stars that make up the far end of the "cup" of the dipper (the side opposite the handle). Draw an imaginary line from the star at the bottom of the cup, through the star at the lip of the cup. Continue this line about four more lengths of that distance, and you'll see a medium-bright star. This is Polaris, the North Star. The constellation Cassiopeia (which looks like a large "W") is about the same distance from the North Star, but on the opposite side of it from the Big Dipper.

3. As the North Star is roughly in line with the Earth's axis of rotation, it never changes position, and measurements can be taken with the quadrant at any time of the night, whatever the season. Use the sight line on the top of the aiming beam to align the beam with the North Star. Use the protractor to measure the angle between the beam and the horizon (which is 90° to the plumb line). This angle is your latitude.