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The Sun Ch 26.1 Spring 2011

The Sun Ch 26.1 Spring 2011. Discovery Science. 0. Guidepost. 0.

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The Sun Ch 26.1 Spring 2011

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  1. The SunCh 26.1Spring 2011 Discovery Science 0

  2. Guidepost 0 The sun is the source of light and warmth in our solar system, so it is a natural object of human curiosity. It is also the one star that is most clearly visible from Earth. The interaction of light and matter, which you studied in Chapter 18, can reveal the secrets of the sun and introduce you to the stars. In this section (26.1), you will discover how the analysis of the solar spectrum can paint a detailed picture of the sun’s atmosphere and how basis physics has solved the mystery of the sun’s core.

  3. Guidepost (continued) 0 • Here you will answer four essential questions: • What do you see when you look at the sun? • How does the sun make its energy? • What are the dark sunspots? • Why does the sun go through a cycle of activity? • Although this chapter is confined to the center of the solar system, it introduces you to a star and leads your thoughts onward among the stars and galaxies that fill the universe.

  4. Outline 0 I. The Solar Atmosphere A. The Photosphere B. The Chromosphere C. The Solar Corona D. Below the Photosphere II. Nuclear Fusion in the Sun A. Nuclear Binding Energy B. Hydrogen Fusion C. Energy Transport in the Sun D. Counting Solar Neutrinos

  5. Outline (continued) 0 III. Solar Activity A. Observing the Sun B. Sunspots C. The Sun's Magnetic Cycle D. Spots and Magnetic Cycles on Other Stars E. Chromospheric and Coronal Activity F. The Solar Constant

  6. General Properties 0 • Average star • Spectral type G2 • Only appears so bright because it is so close. • Absolute visual magnitude = 4.83 (magnitude if it were at a distance of 32.6 light years) • 109 times Earth’s diameter • 333,000 times Earth’s mass • Consists entirely of gas (av. density = 1.4 g/cm3) • Central temperature = 15 million K • Surface temperature = 5800 K

  7. The Solar Atmosphere 0 Only visible during solar eclipses Apparent surface of the sun Heat Flow Temp. incr. inward Solar interior

  8. The Photosphere 0 • Apparent surface layer of the sun • Depth ≈ 500 km • Temperature ≈ 5800 K • Highly opaque (H- ions) • Absorbs and re-emits radiation produced in the sun The solar corona

  9. Energy Transport near the Photosphere 0 Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Cool gas sinking down Bubbles of hot gas rising up ≈ 1000 km Bubbles last for ≈ 10 – 20 min

  10. Granulation 0 … is the visible consequence of convection.

  11. The Chromosphere 0 • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases • Temperature increases gradually from ≈ 4500 K to ≈ 10,000 K, then jumps to ≈ 1 million K Transition region

  12. The Layers of the Solar Atmosphere 0 Ultraviolet Visible Sun Spot Regions Photosphere Corona Chromosphere Coronal activity, seen in visible light

  13. The Magnetic Carpet of the Corona 0 • Corona contains very low-density, very hot (1 million K) gas • Coronal gas is heated through motions of magnetic fields anchored in the photosphere below (“magnetic carpet”) Computer model of the magnetic carpet

  14. The Solar Wind 0 Constant flow of particles from the sun Velocity ≈ 300 – 800 km/s The sun is constantly losing mass: 107 tons/year (≈ 10-14 of its mass per year)

  15. Energy Production 0 Energy generation in the sun (and all other stars): Binding energydue to strong force= on short range, strongest of the 4 known forces:electromagnetic, weak,strong,gravitational Nuclear Fusion = fusing together 2 or more lighter nuclei to produce heavier ones. Nuclear fusion can produce energy up to the production of iron; For elements heavier than iron, energy is gained by nuclear fission.

  16. Energy Generation in the Sun: The Proton-Proton Chain 0 Basic reaction: 4 1H 4He + energy Need large proton speed ( high temperature) to overcome Coulomb barrier (electrostatic repulsion between protons) 4 protons have 0.048*10-27 kg (= 0.7 %) more mass than 4He. T ≥ 1070K = 10 million 0K • Energy gain = Dm*c2 = 0.43*10-11 J per reaction Sun needs 1038 reactions, transforming 5 million tons of mass into energy every second, to resist its own gravity.

  17. Energy Transport in the Sun 0 g-rays Radiative energy transport

  18. Counting Solar Neutrinos 0 The solar interior can not be observed directly because it is highly opaque to radiation. But, neutrinos can penetrate huge amounts of material without being absorbed. Neutrino Detection confirms fusion in the Sun Davis solar neutrino experiment

  19. Very Important Warning: Observing the Sun 0 Never look directly at the sun through a telescope or binoculars!!! This can cause permanent eye damage – even blindness. Use a projection technique or a special sun viewing filter.

  20. Sun Spots 0 Cooler regions of the photosphere (T ≈ 4240 K) They only appear dark against the bright sun; they would still be brighter than the full moon when placed on the night sky!

  21. Sun Spots (2) 0 Active Regions Ultraviolet Sunspot regions show up as bright (active) regions in ultraviolet and X-ray images. Visible

  22. Magnetic Field Lines 0 Magnetic North Pole Magnetic South Pole Magnetic Field Lines

  23. Magnetic Field Lines 0 Hot gas ejected from the sun often follows magnetic field lines and traces out the loop structure of the magnetic field. Video Clip

  24. The Solar Cycle 0 After 11 years, North/South order of leading/trailing sun spots is reversed 11-year cycle Reversal of magnetic polarity => Total solar cycle = 22 years

  25. The Sun’s Magnetic Dynamo 0 The sun rotates faster at the equator than near the poles. This differential rotation might be responsible for magnetic activity of the sun.

  26. Magnetic Loops Video Clip 0 Magnetic field lines

  27. Prominences 0 Relatively cool gas (60,000 – 80,000 oK) May be seen as dark filaments against the bright background of the photosphere Looped Prominences: gas ejected from the sun’s photosphere, flowing along magnetic loops

  28. Eruptive Prominences 0 Extreme events (solar flares) can significantly influence Earth’s magnetic field structure and cause northern lights (aurora borealis). (Ultraviolet images)

  29. Solar Magnetic Phenomena 0 ~ 5 minutes Aurora Borealis Sound waves produced by a solar flare

  30. The Solar Constant 0 The energy we receive from the sun is essential for all life on Earth. The amount of energy we receive from the sun can be expressed as the Solar Constant: Energy Flux F = 1360 J/m2/s F = Energy Flux = = Energy received in the form of radiation, per unit time and per unit surface area [J/s/m2] HEA Video

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