Chapter 21

1. Chapter 21 Characteristics of Stars 21.2

2. Distances to stars • Parallax is the method used by astronomers to study the distance to relatively nearby stars. • Parallax is the apparent change in position of an object when it is observed from a different place

3. Classifying Stars • The 3 Characteristics used to classify stars are Size, Temperature, & Brightness.

4. Sizes of Stars • The Sun is a medium size very ordinary star • Giant Stars are stars much bigger than our star the Sun • A star like Betelgeuse would reach as far as the orbit of Jupiter if it was where our Sun is. • Dwarf Stars are stars that are much smaller than our star • Dwarf Stars are only about 20 kilometers in diameter.

5. Color & Temperature of Stars • A stars color tells you its temperature, their color indicates the size of the wavelength. • The spectrum is used to indicate temperature • Red/Orange stars have the longest wavelengths, thus they have the lowest temperatures • Blue/White stars have the shortest wavelength and have the highest temperatures

6. Brightness • How bright a star looks from Earth depends on how close it is and how much light it is actually giving off

7. Brightness • Apparent Magnitude is how bright a star is as seen from Earth • Star’s brightness is compared to all the other stars you see in the sky. • Sirius is the brightest star in our night sky • Absolute Magnitude is how bright the star would be if it were as far away as our sun. • To find the absolute magnitude an astronomer must first find the apparent magnitude of the star and then find its distance.

8. H-R Diagram • It classifies stars according to absolute magnitude (brightness) and temperature (color). • A diagonal band called the main sequence is where 90% of all stars fall. • Giant stars are to the upper right, and dwarf stars are to the lower left.

9. H-R Diagram