1. Video Field Trip Stars: Life and Death
What happens when stars run out of fuel?
What will happen when to the sun when it dies?

2. Properties of Stars
Chapter 25, Section 1

3. Characteristics of Stars
Color is a clue to a star’s temperature
Very hot (30,000 K) stars emit their light in the blue spectrum, red stars are much cooler, stars with temperatures between 5000 and 6000 K appear yellow
Binary Stars – pairs of stars, pulled together by gravity, that orbit each other
Binary stars are used to determine the star property most difficult to calculate – its mass
The mass of a body can be calculated if it is attached by gravity to a partner

4. Star Temperature

5. Binary Stars

6. Concept Check
What is a binary star system?

7. Measuring Distance to Stars
Parallax is determined by taking a picture of a star at one time, and another picture six months later; using the angle between its apparent shift, astronomers can determine how far away it is
The nearest stars have large parallax angles, while those of distant stars are too small to calculate
Light-Year – unit used to express stellar distance, the distance light travels in one year (~9.5 trillion kilometers)
Our closest star (besides the sun), Proxima Centauri, is about 4.5 light-years away from the sun

8. Parallax

9. Stellar Brightness
Apparent Magnitude – a star’s brightness as it appears to Earth
Three factors control the apparent brightness of a star as seen from Earth: how big it is, how hot it is, and how far away it is
Absolute Magnitude – how bright a star actually is
To determine absolute brightness, astronomers measure how large the star is, what temperature it is, and what its apparent brightness would be at 32.5 light-years

10. Stellar Brightness

13. Concept Check
What is the difference between apparent magnitude and absolute magnitude?

14. Hertzsprung-Russell Diagram
A Hertzsprung-Russell diagram shows the relationship between the absolute magnitude and temperature of stars
Main-Sequence Star – This category contains the majority of stars and runs diagonally from the upper left to the lower right on the H-R diagram
Red Giants – a large, cool star of high luminosity
Supergiants – a very large, very bright red giant star
Cepheid Variables – A star whose brightness varies periodically because it expands and contracts, a type of pulsating star
Nova – A star that explosively increases its brightness

15. Hertzsprung-Russell Diagram

16. Concept Check
The H-R diagram shows the relationship between what two factors?

17. Interstellar Matter Nebulae – clouds of dust and gases in space
Emission nebulae consist largely of hydrogen, they absorb ultraviolet radiation emitted by nearby stars
Reflection nebulae merely reflect the light of nearby stars
Astronomers like to study nebulae because stars and planets form from them

18. Dark Nebula – Horsehead Nebula

19. Assignment Read Chapter 25 Section 1 (pg. 700-706)
Do Section 25.1 Assessment #1-7 (pg. 706)