How Stars are Classified

1. How Stars are Classified Temperature Brightness

2. Color of Stars Class O – Blue Star • Surface Temperature: 30,000+ C • Elements: Helium • Examples: 10 Lacertae Class B – Blue White • Surface Temperature: 10,000 to 30,000 C • Elements: Helium and Hydrogen • Examples: Rigel, Spica

3. Color of Stars Class A Blue - White • Surface Temperature: 7500 to 10,000 • Elements: Hydrogen • Examples: Vega, Sirius Class F Yellow - White • Surface Temperature: 6000 to 7500 C • Elements: Hydrogen and heavier elements • Examples: Canopus, Procyon

4. Color of Stars Class G Yellow • Surface Temperature: 5000 to 6000 C • Elements: Calcium and other metals • Examples: the Sun, Capella Class K Orange • Surface Temperature: 3500 to 5000 C • Elements: Calcium and molecules • Examples: Arcturus, Aldebaran

5. Color of Stars Class M Red • Surface Temperature: less than 3500 C • Elements: Molecules • Examples: Betelgeuse, Antares

6. How Bright is the Star? • First Magnitude: brightest stars in the sky. • Magnitude means size or in this case, brightness. • Sixth Magnitude: faintest stars in the sky • Apparent Magnitude is how bright a light looks. • Absolute Magnitude is the actual brightness of a star • Example: Our sun’s absolute magnitude +4.8; apparent magnitude –26.8

7. Distance to the Stars • A light year is the distance that light travels in one year. • The speed of light is about 300,000 km/s. • It travels about 9.5 trillion km in one year. • Light years make it easier to give distances without using large numbers.

8. Distance to the Stars • A parallax is the apparent shift in position by a star. • Used with trigonometry to calculate distances of stars near to the Earth. • Farther stars are measured in more complicated ways.

9. How Long is a Light Year • 20 light years away, look at White House • Who is president and who is the first lady? Answer: 20 light years away is 1992 Clinton elected but did not take office until 1993 Answer – George H. W. Bush – wife Barbara

10. How Long is a Light Year Worksheet Year 2000 – you are on a planet 94.6 trillion kilometers away from Earth How old is the child on Earth at the time you are watching the child’s 3rd birthday? Light year is 9.5 trillion kilometer 94.6 divided by 9.5 = approximately 10 light years 10 + 3 = 13 years old

11. How Long is a Light Year Worksheet Are any of the 9 planets within our solar system a light year away or more from Earth? Pluto is 5,913,520,000 miles from Earth (5.9 trillion) 1 light year is 9,500,000,000 miles (9.5 trillion) Answer is No Measure distances of planets in astronomical units (AU)

12. Hertzsprung-Russell Diagram • Graphic representation of the star spectrum classification. • Stars are plotted according to their temperature and luminosity (brightness).

13. Hertzsprung-Russell Diagram Luminosity is determined by measuring a star’s brightness and determining its distance. Scientists measure the temperature of a star by observing the color of the star. Has 3 distinct groups: main sequence, red giants, white dwarfs

14. Main Sequence • A narrow, diagonal bands of stars • Stars are burning hydrogen • Spend first and longest stage of life here

15. Red Giants • Cool Luminous Stars • Found in upper right of HR Diagram • To be bright, these cool stars must be very large • As Main Sequence stars use up their fuel, they become Red Giants.

16. White Dwarfs Faint Hot stars Found in lower left of HR Diagram Many stars end their life in this location

17. Using A Hertzsprung-Russell Diagram Absolute Magnitude • Shown on the Y axis • The bottom of the chart indicate low absolute magnitude. • The top of the chart indicate high absolute magnitude. Temperature • Shown the x axis. • Temperatures get hotter as the star moves to the left side of the diagram. • Temperatures get cooler as the star moves to the right of the diagram.