CIRCUMPOLAR STARS Lesson Objectives To explain the apparent

CIRCUMPOLAR STARS

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.

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. http: //www. gcseastronomy. co. uk/space/ani mation/flash_circumpolar. html http: //www. gcseastronomy. co. uk/space/an mation/flash_UKstars. html

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

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

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 (19 N) 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.

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.

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