The Sun!

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

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

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

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)

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?

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

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?

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

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)

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

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

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.

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

Planetary Nebula – Spitzer Space Telescope

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?

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?

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

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.