Cepheid Variables

Slideshow Transcript

1. Slide 1: Cepheid Variables
2. Slide 2: How does a star work ? • Gravity tries to compress the star.
3. Slide 3: • Heat from nuclear fusion pushes out
4. Slide 4: • Star in a position of equilibrium ( balanced forces.
5. Slide 5: • Many stars pass through a period of instability during their lives.
6. Slide 6: • Cepheid Variables are yellow supergiants with a mass over 3x the mass of the sun • They pulse in periods of a few days.
7. Slide 7: • Their brightness can be measured
8. Slide 8: Why does it pulse ?
9. Slide 9: • So how can we measure the distance of stars?
10. Slide 10: What do we know ? • 1. The further a star is away, the dimmer it will seem. • 2. The size of the star is important in deciding how bright it is. • 3. We need to know the type of star ( e.g. White dwarf, red giant)
11. Slide 11: • So its temperature is important too
12. Slide 13: • Red Giants are large but cool • White dwarfs are small but hot.
13. Slide 14: • So The distance and the temperature are key factors in deciding the brightness of stars.
14. Slide 15: • So why are Cepheid variables important? • We can use them to measure their distances from Earth. • Gives us a capability of measuring more distant objects . • Better than parallax.
15. Slide 16: • From their period, we can calculate their Absolute magnitude ( apparent magnitude it would have if it is 10 parsecs from Earth) • We can measure its apparent magnitude. • The distance can be calculated from the Absolute and apparent magnitude using a simple formula.
16. Slide 18: Remember from P1 • The Great Debate of 1920 • Harlow Shapley said nebula were part of the Milky Way. • Heber Curtis claimed that spiral nebulae were star systems outside the Milky Way.
17. Slide 19: • Shapley won the debate but Curtis was later proved to be right. • Edwin Hubble used a 100 inch telescope to discover Cepheid variables in the Andromeda nebula and in other spiral clusters of stars. • These turned out to be much further away than stars in our own galaxy.
18. Slide 20: • Hubble used Cepheid variables to measure the distances of many local galaxies e.g. 2.5 million light years away. • Most galaxies were too far away to pick out Cepheid variables • The Milky Way is 100,000 light years in diameter.