1. Characteristics of Stars
Chapter 21, Section 2
Characteristics of Stars

2. Distance to Stars Measuring distances with Parallax
Light-year- The distance that light travels in one year, it is about 9.5 trillion kilometers ( that is 9.5 million million kilometers)
Measuring distances with Parallax
Parallax is the apparent change in position of an object when you look at it from different places
Used only for nearby stars by looking at how stars move as the Earth goes around the sun.

3. The main characteristics used to classify stars are Size Temperature
Classifying Stars
The main characteristics used to classify stars are
Size
Temperature
Brightness

4. Sizes of Stars
Many stars are about the size of the sun the sun is medium-sized
Very large stars are giant stars or supergiant stars
-The Supergiant Betelgeuse would extend out to Jupiter if it was in sun’s position
White dwarfs are Earth-sized
Neutron stars are only 20km in diameter

5. Color and Temperature of Stars
A star’s color reveals its temperature
Cool stars burn RED 3200°C
Hottest stars are bluer than white
and are blue-white burning at 10,000°C
The sun glows white at 5500 C

6. Brightness of Stars Brightness depends on size and temperature
Apparent magnitude- is brightness as seen from Earth
Absolute magnitude- is brightness the star would have if at a standard distance from Earth

7. Hertzsprung-Russell Diagram
H-R Diagram is a graph relating the temperature and brightness of stars
-Brightness increases moving up y-axis
- Temperature decreases moving right on x-axis
More than 90% of all stars are in a diagonal band called the Main sequence
- In the main sequence, temperature increases as brightness increases
- The sun is in the main sequence

8. Hertzsprung-Russell Diagram
Upper right side of H-R diagram contains giant and supergiant stars
White dwarfs are hot but not bright so the are at the bottom center of the H-R diagram

9. Hertzsprung-Russell Diagram9
Image from