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What are Circumpolar Stars?

A circumpolar star does not set, i.e. it is above the horizon all the time. What stars are circumpolar for a particular observer will depend on their latitude.

Circumpolar Stars
Image via: starlight-nights.co.uk

Notice the following:

  • The pole star is 55 degrees above the horizon. Remember your latitude is equal to the altitude (angle above the horizon) of Polaris.
  • Any star with a declination of 35 degrees will just skim the horizon at this latitude.
  • Any star with a declination > 35 degrees will be circumpolar. (In the sky all the time.   35 = 90 – 55)
  • In general, from latitude L, any star with a declination greater than 90 – L will be circumpolar.
  • Any star with a declination of 55 degrees could be at the zenith (directly overhead)

Still confused? Here’s another way of looking at declination calculations you might find easier to understand.

Circumpolar Stars equation
Image via: vikdhillon.staff.shef.ac.uk

 

Circumpolar Stars equation 2
Image via: WSU Astronomy

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