A100 The Sun

1. A100 The Sun • Read Chapter 11 • Homework and Quiz 9 this week on Friday • Last Solar Lab on TOMORROW at NOON Today’sAPOD The Sun Today

2. Basic Facts • radius • 7 x 105 km • about 100 x Earth’s radius • mass= about 300,000 x Earth’s mass • distance • 1 AU, 8 light minutes • 1.5 x 108 km • about 100 x Sun’s diameter • Temperature • about 6000Kelvin (10,000 F) at the surface • about 15 million Kelvin inside • Composition • 90% of atoms are hydrogen • 10% of atoms are helium The Sun WHY WE STUDY THE SUN

3. With helioseismology, we can measure temperature, pressure and motion inside the Sun from sound waves that traverse the Sun’s interior. Helioseismology

4. Helioseismology Listen to the Sun blue = inward motion red = outward motion The Sun oscillates in complex patterns over the whole interior and surface. The frequency and location of the oscillations give us a detailed picture of the inside of the Sun.

5. Basic Structure INSIDE Core Radiative Zone Convection Zone OUTSIDE Photosphere Chromosphere Corona Solar Wind

6. Conditions inside the Sun Temperature peaks in the core and drops off at the outside edge of the Sun

7. Why does the Sun Shine? • The Sun is a “cooling ember” • The Sun is burning like coal or wood • The Sun is contracting due to gravity NONE OF THESE PRODUCES ENOUGH ENERGY

8. NUCLEAR REACTIONS produce enough energy E = mc2 - Einstein, 1905 Nuclear Potential Energy (core) ~ 10 billion years Luminosity

9. What produces nuclear energy? Fusion: Small nuclei stick together to make a bigger one Fission: Big nucleus splits into smaller pieces

10. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Nuclear fusion requires high temperatures and high density

11. The Sun’s Energy Comes from Nuclear Fusion The Conversion of hydrogen into helium

12. Proton-proton chain fuses hydrogen into helium IN:4 protons OUT: 4He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower • The missing mass is converted to energy • Rate of nuclear fusion depends on temperature

13. How do we know nuclear reactions are going on in the Sun? • Neutrinos created during fusion fly directly out of the Sun • These neutrinos can be detected on Earth

14. Estimating the Sun’s Lifetime The Sun’s Lifetime • How much fuel does the Sun have? • How fast is that fuel being consumed? • When will it run out?

15. How much fuel? • The Sun “burns” hydrogen to helium in a nuclear reaction • How many hydrogen atoms in the Sun • 2 x 1033 grams of hydrogen • 6 x 1023 atoms in each gram E = mc2 12 x 10 56 hydrogen atoms

16. How Much Energy Can the Sun Produce? E = mc2 • For each helium nucleus created, the Sun produces 5 x 10-12 joules of energy • the Sun can burn half its hydrogen • FOUR hydrogen atoms are needed to make each helium atom ½ x ¼ x 12x1056 x 5x10-12 = 7 x 10 44 joules

17. The Solar Constant 1400 watts = 14 100-watt light bulbs • How Much Energy Each Second? • At the distance of the Earth, the Sun radiates 1400 watts (1400 joules per second) in each square meter on the surface of a sphere with a radius equal to one AU • How many square meters are on that sphere? What is a joule? Each second a 100-watt light bulb produces 100 joules of energy 1 meter

18. Sphere with radius of 1 AU Surface area of a sphere = 4pr2 How many square meters on a sphere with radius one AU? Area times energy per square meter per second equals total energy output per second The Sun produces 4 x 1026 watts

19. Solar Energy How long will the Sun shine??? From the conversion of hydrogen into helium by nuclear reactions… E = mc2 Total energy available = 7 x 1044 joules Radiating energy at 4 x 1026 joules per second Lifetime = 7 x 1044 joules 4 x 1026 joules per second = 2 x 1018 seconds = 6 x 1010 years

20. Solar Energy How long will the Sun shine??? E = mc2 In fact, the Sun will only shine for about 10 billion years, twice its present age. Not all the Sun’s hydrogen is in regions hot enough for hydrogen fusion reactions to occur.

21. How does the energy from fusion get out of the Sun? • Radiation • Convection

22. How does the energy from fusion get out of the Sun? Radiation: In the inner regions of the solar interior, energy gradually leaks upward in form of randomly bouncing electromagnetic waves. As the energy propagates outward, the electromagnetic energy shifts from gamma rays and X-rays to ultraviolet and optical light

23. Energy Transport In the outer regions of the Sun’s interior, energy flows outward by convection; heat is carried upward by bubbling hot gas. time lapse movie

24. The convection zone gives the surface the appearance of boiling liquid

25. Balancing Gravity Gravitational contraction: Provided energy that heated core as Sun was forming Contraction stopped when fusion began Gravitational equilibrium: Energy provided by fusion maintains the pressure

26. The Solar Thermostat Decline in core temperature causes fusion rate to drop, so core contracts and heats up Rise in core temperature causes fusion rate to rise, so core expands and cools down

27. Summary: • Why was the Sun’s energy source a major mystery? • Chemical and gravitational energy sources could not explain how the Sun could sustain its luminosity for more than about 25 million years • Why does the Sun shine? • The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion.

28. Dates to Remember • Ch 11 – The Sun • Quiz, Homework on Friday • Solar Lab tomorrow at NOON