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.
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.