Are the circumpolar stars the same everywhere on Earth?
Provide a reason to support your answer.

To explore the answer to this question, change viewing locations in Starry Night (see Procedure 1). From the viewing location of the equator, observe the motion of the stars using Polaris as a focal point.

What do you observe about the apparent motion of the stars? With Polaris just in view just on the horizon, it appears that all stars rise and set at the equator. Now, change your viewing location to the North Pole, again using Polaris as the focal point.

What do you observe about the apparent motion of the stars from this location?

You should notice that all stars from this location appear to be circumpolar!




Viewing from near the equator, note Polaris a few degrees above the horizon in the above screenshot.

Try developing possible explanations for the observations you have made.

Why do we say "it appears" that stars are moving across the night sky?

The apparent movement is due primarily to earth's rotation. Stars somewhat near the pole, called circumpolar stars, will trace out circles about the pole as the night progresses, turning approximately 15° per hour. Of course, it is really the earth that is turning, but it appears that the stars are moving.

Try viewing the northern constellations from other geographic locations and consider the following questions:

Where on earth would you expect to observe the fewest circumpolar stars?

At the equator, all stars appear to rise and set.

Where on earth would you expect to observe the most circumpolar stars? Why?

At the poles all stars appear to rise and set.

How does the position of Polaris above the horizon affect the number of circumpolar stars?

There is a direct relationship between Polaris's altitude above the horizon and the number of observed circumpolar stars; the higher above the horizon the greater number of circumpolar stars.


Procedure 1  |   2  |   3