2. Stars Properties: Brightness and Color Reasons for brightness: Proximity Temperature of star

3. Parallax The angle of the parallax, θ, in arcsecs is equal to the distance, D, by the following formula: D = 1/θ here the distance, D, is measured in parsecs, where one parsec equals 3.26 light-years (the distance travels in one year).

4. PROPER MOTION Although the stars appear fixed in the sky, they are actually moving through space at very high velocities. Extremely large distances makes this motion almost undetectable..

5. The diagram shows how the Big Dipper will look after 10,000 years.

6. Apparent magnitude Ancient astronomers divided stars into six classes or magnitudes where the brightest are first magnitude, the faintest are sixth magnitude. Later measurements showed that a change in 5 magnitudes is equal to a 100 increase in brightness.

7. Object Apparent Mag Sun -26.5 Full Moon -12.5 Venus -4.0 Jupiter -3.0 Sirius -1.4 Polaris 2.0 eye limit 6.0 Pluto 15.0 limit for telescopes 25.0

8. Absolute magnitude If the apparent magnitude of a star is m and its absolute magnitude is M (its real brightness), then the distance to the star, d in parsecs, is given by: m = M + 5 log (d/10)

9. Solar neighborhood

10. Stefan-Boltzmann law: the amount of energy emitted from a body increases with higher temperature Wien's law: the peak of emission moves to bluer light as temperature increases

11. Some stars have a strong signature of hydrogen (O and B stars), others have weak hydrogen lines, but strong lines of calcium and magnesium (G and K stars). After years of cataloging stars, they were divided into 7 basic classes: O, B, A, F, G, K and M. Note that the spectra classes are also divisions of temperature such that O stars are hot, M stars are cool. Between the classes there were 10 subdivisions numbered 0 to 9. For example, our Sun is a G2 star. Sirius, a hot blue star, is type B3.

12. Type Mass Temp Radius Lum (Sun=1) O 60.0 50,000 15.0 1,400,000 B 18.0 28,000 7.0 20,000 A 3.2 10,000 2.5 80 F 1.7 7,400 1.3 6 G 1.1 6,000 1.1 1.2 K 0.8 4,900 0.9 0.4 M 0.3 3,000 0.4 0.04

13. A “B star” is much larger, brighter and hotter. An example is HD93129A shown:

14. Aldebaran is a red supergiant star:

15. Arcturus is an orange giant star: :

16. Betelgeuse is one of the largest stars, almost the size of our whole solar system