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A105 Stars and Galaxies

A105 Stars and Galaxies. News Quiz Today Review Exam 1 Homework 6 (the Sun) due Thursday. Today’s APOD. Announcements…. Solar Lab today at 11, tomorrow at 2 PM Kirkwood Obs. Moon Festival, Oct. 4, 8:30-10:30 Rooftop Session, Oct. 4, 9:00

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A105 Stars and Galaxies

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  1. A105Stars and Galaxies • News Quiz Today • Review Exam 1 • Homework 6 (the Sun) due Thursday Today’sAPOD

  2. Announcements… • Solar Lab today at 11, tomorrow at 2 PM • Kirkwood Obs. Moon Festival, Oct. 4, 8:30-10:30 • Rooftop Session, Oct. 4, 9:00 • Orionid meteor shower, Oct. 21-22, just before midnight

  3. Exam Review • Range of score: 24-76 of 80 questions • Average score: 54/80 NovaSearch I Homework • If you picked a year with just a few observations available, you will need to select another year with more for NS II and NS III! • If the year you selected did not seem to show any blemishes, view some other years to see what they look like.

  4. News Quiz • On a piece of paper, list three important ideas from this week’s audio selection • Print your name carefully – if we can’t read your writing, we can post the points to the gradebook!

  5. The Sun Today • Image credit: Solar Orbiting Heliospheric Observatory/MDI

  6. The Sun • 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 WHY WE STUDY THE SUN

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

  8. 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.

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

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

  11. 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

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

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

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

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

  16. 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

  17. 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

  18. 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?

  19. 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

  20. 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

  21. The Solar Constant • 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? 1400 watts = 14 100-watt light bulbs What is a joule? Each second a 100-watt light bulb produces 100 joules of energy 1 meter

  22. 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

  23. 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

  24. Solar Energy How long will the Sun shine??? In fact, the Sun will only shine for about 10 billion years, twice its present age. E = mc2 Not all the Sun’s hydrogen is in regions hot enough for hydrogen fusion reactions to occur. We’ll learn more about the future evolution of the Sun as we look more closely at other stars in the Galaxy.

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

  26. 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. Further from the center, the wavelengths of the electromagnetic waves become longer.

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

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

  29. 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

  30. 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

  31. 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.

  32. The Budget of Solar Radiation What happens to sunlight that falls on the Earth?

  33. Recall the structure of the Sun…

  34. Corona The Sun’s Atmosphere: Photosphere, Chromosphere, Corona, Solar Wind

  35. For This Week... • The Sun! Units 49, 50, 52 • Homework 6 Due THURS. SOLAR LAB TODAY AT 11:00, TOMORROW AT 2:00

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