1. Stars 2-1; part 2 How Bright is that Star?

2. What can you say about the brightness of the street lights as they appear in this picture? Can we use the same understanding of light to estimate distances to stars?

3. Apparent Magnitude Apparent magnitude is the brightness of a star as it appears from Earth.

4. Absolute Magnitude Absolute magnitude uses a stars apparent magnitude and its distance from Earth to calculate its true brightness. It’s actual brightness compared to other stars if they were all at the same distance from Earth.

5. Absolute Magnitude Absolute magnitude is calculated by comparing what a stars brightness would be at 10 parsecs from Earth (~32.6 LY) Our Sun would have a magnitude of +4.8. Compare this to it’s apparent magnitude of -26.8 because it is so close to the Earth.

6. Absolute Magnitude vs. Apparent Magnitude http://www.teachertube.com/members/view Video.php?video_id=104918www.teachertube.com/members/view Video.php?video_id=104918

7. Distance to the Stars Stars closer to Earth seem to move, while more distant stars seem to stay in one place as the Earth revolves around the Sun. A stars apparent shift in position is called parallax. Using parallax, astronomers can find distances to stars that are close to Earth.

8. Quick Lab

9. Parallax

10. How Parallax Determines Distance The smaller parallax angle, the farther the star

11. Motion of stars Notice that we see a different sky in June than we see in December. This is why we see different constellations during different seasons

12. Apparent motion of stars Because of the Earth’s rotation-the night stars appear to move around the North Star (Polaris) Polaris

13. 9.28 min video of Sun, Earth movements