1. The Sun!

2. About 5 billion years ago, the sun was born
A nebula is a cloud of hydrogen gas where stars form
Soon after the nebula collapsed to form the proto sun, there was a disk of gas and dust surrounding the sun

3. The Protosun
The disk surrounding the sun only lasted for 10 million years. What became of it?

4. Page 26 Outline Nebula collapsed to form protosun
Nearly all the gas and dust fell into the protosun
The rest became a solar nebular disk that lasted 10 million years
The particles collided  planetesimals  asteroids
Eventually formed our solar system
Rocky planets close to sun, gas giants further out
We don’t know exactly how we got to an elegant solar system

5. Hydrogen and Helium The sun is 75% Hydrogen The sun is 25% Helium
The Hydrogen in the sun is a plasma, its electrons have come apart from the nucleus of the atom
The sun fuses hydrogen atoms into helium (nuclear fusion)

7. Read & Outline! Read & Outline page 30 from the textbook on the sun:
Nuclear Fusion
The sun as a star
What happens when the sun dies?

8. Page 30 Outline
After 100 million years of contraction nuclear fusion began
Reached critical pressure and temperature to start nuclear fusion
The sun is an average star
Sun will fuse hydrogen into helium for 5 billion more years
Sun will shed outer layers, engulf earth
Fuse helium
Helium runs out sun  white dwarf
500 million stars are born and 500 million stars die each day

9. Discuss at your table and write in your notebook:
How does the sun compare to other stars? How does the birth of the sun affect life on earth?

10. Nuclear Fusion in the sun
Two hydrogen atoms fuse together (join together)
Becomes helium
Takes less energy to hold the helium atom together
Excess energy is released and radiates to earth

12. Discovery of Nuclear Fusion 1939
astrophysicists knew the sun had extremely high temperatures and pressure
Didn’t know how the sun generated energy
Had done experiments on nuclear transmutation (changing one element to another)

13. Bethe and Weizsacker
They independently described how nuclear fusion in the sun could occur
Realized that nuclear fusion could be created on earth
Lead to the development of nuclear power
Lead to the atomic bomb

15. Death of the Sun Know from comparisons to other stars
Our sun had a violent birth, 10-billion years of relative stability, and then will die
How far along it’s life cycle is the sun right now??
Sun is slowly getting hotter as more hydrogen is used up
In one billion years, oceans will evaporate

16. 250x the current size! Red Giant Star
Guess how many of the sun can fit inside of the red giant.
Closest guess gets a point on class dojo.

17. When the sun is a red giant, will it be hotter or cooler?
Wein’s law: The longer the wavelength, the lower the temperature

19. Planetary Nebula – Spitzer Space Telescope

20. Red Giant  White Dwarf Sun will swell 250x engulfing the earth
Outer layers will be pushed out to deep space as a Planetary Nebula
Planetary Nebula will become new stars
Remains of the suns core will become a white dwarf
Slowly cools to nothing
Perhaps by then humans will inhabit other planets?

21. Think pair share: What is a white dwarf
Think pair share: What is a white dwarf? How will the death of the sun form new stars?

22. Poster Session
Individually, or in a PAIR (no groups of three) create a poster to show the death of the sun.
Runs out of hydrogen
Red giant
Planetary Nebula
White dwarf

23. Next Unit: Stars!
Outline page 252 in your notebook We will share our outlines afterwards This relates to the episode of Cosmos we will watch.