1. Circumpolar Stars

2. Lesson Objectives
• To explain the apparent motion of stars around Polaris.
• To understand the conditions for a star to be circumpolar from a given latitude.

3. What are Circumpolar Stars
Circumpolar stars are stars that can be seen from one location throughout the year. Other stars are usually only seen for a month or two.

4. Why do stars revolve around Polaris?
To explain the apparent motion of stars around Polaris.
Why do stars revolve around Polaris?
Stars appear to revolve around Polaris in the Northern Hemisphere. As the Earth rotates stars appear to revolve around that star because it is above the Earth’s northern axis.
In the exam you may be asked to determine:
• Which stars are circumpolar and which are not.
• What latitude you would have to be at in order to see a certain star
• The smallest or largest Declination (The angular distance of a point north or south of the celestial equator) a star would be at from a given latitude

5. To understand the conditions for a star to be circumpolar from a given latitude.
Circumpolar Formula
The formula for working out if a star is circumpolar or not is:
D >= 90° - L
D = Declination
>= = Greater than or equal to
L = Latitude of observer

6. Example 1 Deneb = Dec 45 degrees Arcturus = Dec 19 degrees
Alpha Centuri = Dec -61 degrees
If you were in London would Deneb be circumpolar?
90 - L (51) = 39
45 is greater than 39 so Deneb is circumpolar
Arcturus (19N) is less than 39 so is not circumpolar but seasonal
Alpha Centuri has a declination -61 is less than 39 and so would not be viewable from London.

7. Apply Your Knowledge
State whether or not each of these stars would be: Visible from New York (41°N) or Sydney (34°S) and circumpolar from either city or seasonal.
Also state the minimum latitude (north and south) they would have to be seen from to be circumpolar.
Key: New York = NY, Sydney = SY.

8. Review
What have you learned in todays lesson? Write a paragraph to music.