Understanding Star Brightness: Apparent and Absolute Magnitude Explained

1. Stars 2-1; part 2 How Bright isthat Star?

2. Whatcanyousay about the brightness of the street lights as theyappear in thispicture? 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 itappearsfromEarth.

4. Absolute Magnitude • Absolute magnitude uses a stars apparentmagnitude and its distance fromEarth to calculateitstruebrightness. It’sactualbrightnesscompared to other stars if theywere all at the same distance fromEarth.

5. Absolute Magnitude • Absolute magnitude iscalculated by comparingwhat a stars brightnesswouldbeat10 parsecs fromEarth (~32.6 LY) • Our Sun would have a magnitude of +4.8. Compare this to it’s apparent magnitude of -26.8 becauseitisso close to the Earth.

6. Absolute Magnitude vs. Apparent Magnitude http://www.teachertube.com/members/viewVideo.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 Polaris Because of the Earth’s rotation-the night stars appear to move around the North Star (Polaris)

13. 9.28 min video of Sun, Earthmovements