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How to Tell if a Star Is Circumpolar

Hundreds of years before satellites, GPS and radar, people used the night sky to navigate. Lacking any light pollution, the stars shone brightly each night. Some of these stars rose and set like the moon, while others circled overhead in the darkness, never setting, always visible. These circumpolar stars became important landmarks in the sky, and navigators and explorers quickly learned how to identify which stars would never set. Finding a circumpolar star is easy, fast and requires no equipment.

Things You'll Need

Star chart

Instructions

- 1
  Find the Big Dipper. This star formation is part of Ursa Major, the big bear, one of the most recognizable constellations in the sky. A star chart will show the shape of the constellation.
- 2
  Create an imaginary line connecting the two stars that make up the the far wall (not the bottom) of the scoop, furthest away from the handle of the constellation. Extend that line in a gentle arc higher into the sky, moving away from the horizon. The imaginary line will intersect a medium intensity star as it crosses due north. This is Polaris, the north star.
- 3
  Mark or reference the location of Polaris. This star's location never changes during the night because it is centered on Earth's extended axis; every star in the sky revolves around Polaris.
- 4
  Calculate Polaris' astronomical altitude, in degrees, using the hand and fist method. Hold your outstretched arm at the horizon and make a fist. Your fist should be positioned with the clenched little finger resting on the horizon and the rest of the fist extending into the sky. Each fist is approximately 10 degrees of altitude. Esitmate, to the nearest five degrees, the altitude of Polaris. Astonomical altitude is also referred to as a star's angular distance from the horizon.
- 5
  Calculate the angular distance between Polaris and another star using the hand and fist method. If the stars are far apart, use a spread-out hand instead of a fist. Approximately 20 degrees separate the tip of the thumb and the tip of the little finger.
- 6
  Compare Polaris' altitude against the angular distance between the two stars. A circumpolar star will have a smaller angular distance than Polaris's altitude. For example, the angular distance between Polaris and star B is 15 degrees, while Polaris's altitude is 35 degrees. Star B, therefore, is circumpolar.

Astronomy