Circumpolar Stars

demonstrate an understanding that the elevation of Polaris above the northern horizon is equal to the latitude of the observer
describe what is meant by the term ‘circumpolar stars’ and explain the connection between the apparent motion of stars and the Earth’s rotation
demonstrate an understanding that a star will be circumpolar from a given latitude provided declination > 90 – latitude


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.

Study the diagram below. I happen to live in Middlesbrough which has a a latitude of 55 degrees though in the exam it could be any 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)

 

There will be a question based on understanding this in the exam so make sure you do. You might find it useful to do a sketch like the one above to help you figure it out.

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





e.g. if you were at a latitude of 52 degrees