How to Use Constellations to Tell Time

Telling time by the constellations of stars is a useful skill. While it is complicated to get an extremely accurate time, the general idea is fairly simple. The basic method uses Polaris, the North Star. This star is on a direct line with the northern axis of Earth, making it a superb reference point. Unfortunately, this method is not useful in the southern hemisphere. Due to an extra rotation of the Earth, in relation to the stars, time calculated using stars is slightly off from the time we know based on the sun. This is called sidereal time. You can account for it easily when you tell time by the constellations.

Things You'll Need

  • None
Show More

Instructions

  1. North Star

    • 1

      Find the North Star, Polaris. If you look at the Big Dipper in the northern sky at night, the two stars that make up the side of bowl farthest from the handle point directly to the North Star. These two stars are called Merak and Dubhe. Polaris is actually part of the Little Dipper, though most of the stars in the Little Dipper are fainter than the stars in the Big Dipper.

    • 2

      Use Polaris as the center of a 24-hour clock that turns counter clockwise. Imagine lines every 15 degrees around this clock that emanate from Polaris.

    • 3

      When Merak and Dubhe are on a line directly to the left of Polaris, it is about 11 o'clock.

    • 4

      Account for the day. The Earth rotates around the sun, but because of its axis, the Earth achieves what amounts to one extra rotation throughout the year. This amounts to about four minutes a day. So if you take the time today and tomorrow, Polaris will be in the same position four minutes later tomorrow.