1. Star Classification

2. Classifying Stars
What are some ways that we could group these stars? How do you think scientists group stars?

3. Analysis Questions
How did your lab group choose to classify the stars?
What additional ways do you think that scientists classify stars?
What did you notice about the star’s color and temperature?

4. We Classify Based on Characteristics
Stars are huge balls of glowing gas that produce energy through fusion.
Stars looks so small because they are so far away.
Only a few thousand stars can be seen without a telescope.
Light Year – the distance that light travels in one year.
Equivalent to 9.5 trillion kilometers or 24 trillion miles.
Sun is our closest star, and the next closest is Alpha Centauri which is 4.3 light years away.

5. Brightness Some stars are brighter than others.
The distance between the star and Earth, and the amount of light a star gives off determines the star’s brightness.
Stars close to Earth can appear bright, even if they do not give off much light. Additionally, very bright stars may appear faint if they are far away.
Apparent magnitude: brightness of the star as it appears from earth
Absolute magnitude: the brightness of the star determined scientifically
Proxima Centauri

6. Distance
Parallax – the apparent shift in position of an object when viewed from different locations.
This is how we determine a star’s distance from us.

7. Size
The diameter of the Sun is about 100 times larger than the diameter of the Earth.
The mass determines how big a star will become. (Write into notes!!)
Stars can be bigger than the Sun!
Giant and Supergiant stars are larger.
Betelgeuse is 600 times greater in diameter than the Sun.
Stars can be smaller than the sun!
White dwarfs are smaller than the Sun.
About 100 times smaller than the Sun’s diameter.
Size of Earth
The sun will end its life as a black dwarf.

8. Color and Temperature
Stars vary in color. These differences are because of the difference in temperature.
We group stars by color.
Blue  White  Yellow  Orange  Red
As you read colors from left to right, blue is the hottest star to red the coolest temperature.

9. Hertzsprung–Russell diagram

10. Based off of this data, what is the best way to classify these stars?
A. Color
B. Temperature
C. Brightness
D. Size
Star #
Known Information 45
6,000 degrees Celsius 78
7,000 degrees Celsius
239
10,000 degrees Celsius
789
8,000 degrees Celsius
7855
1,000 degrees Celsius
391

11. Based off of this data, what is the best way to classify these stars?
A. Color
B. Temperature
C. Brightness
D. Size

12. Based off of this data, what is the best way to classify these stars?
A. Color
B. Temperature
C. Brightness
D. Size

13. Star Classification Wrap-up
Stars are divided into five (5) main groups: Neutron Stars, Dwarf, Medium-sized, Giants and Supergiants
Composition (what stars are made of) is determined by the use of a spectroscope. This instrument breaks up the visible light into its chararteristic colors.
Hydrogen is the most common element in a stars composition. Helium is the next most common element. These 2 elements compose approximately 96-97% of a star.

14. Star Classification Wrap-up
The color of a star is determined by its surface temperature. What are the colors from the hottest to the coolest?
The brightness of a star depends on its size, temperature and distance from the Earth.
Nuclear fusion is the process of changing (or fusing) atoms of hydrogen into helium atoms. During this nuclear fusion process, energy and light are also created which is why a star shines.
The Hertzprung-Russell Diagram shows the direct correlation between the stars absolute magnitude and its temperature.

15. Exit Ticket 1. How is a star’s temperature related to its color?
2. Is a blue star hotter or cooler than a red star?
3. What are two factors that impact how bright a star appears to us on earth?
4. What is the apparent magnitude of a star?