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Ch9Ch9
The Sun, Our Star
• The Sun is an average star.• From the Sun, we base our
understanding of all stars in the Universe.
• No solid surface.
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Vital Statistics
• Radius = 100 x Earth (696,000 km)• Mass = 300,000 x Earth (1.99 x 1030
kg)• Surface temp = 5,800 K• Core temp = 15,000,000 K• Luminosity = 4 x 1026 Watts• Solar “Day” =
– 24.9 Earth days (equator)– 29.8 Earth days (poles)
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In The Core
• Density = 20 x density of Iron
• Temperature = 15,000,000 K
• Hydrogen atoms fuse together.
• Create Helium atoms.
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Nuclear Fusion• 4H He• The mass of 4 H nuclei (4 protons):
4 x (1.6726 x10-27 kg) = 6.690 x 10-27 kg• The mass of He nuclei: = 6.643 x 10-27 kg• Where does the extra 4.7 x 10-29 kg go?• ENERGY! E = mc
• E = (4.7 x 10-29 kg ) x (3.0 x 108 m/s)2
• E = hc/ = 4.6 x 10-14 m (gamma rays)• So: 4H He + light!
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Solar Cross-Section
• Progressively smaller convection cells carry the energy towards surface.
• See tops of these cells as granules.
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Aurorae
• The solar windpasses outthrough theSolar System.
• Consists of electrons, protons and other charged particles stripped from the Sun’s surface.
• When charged particles and magnetic fields interact: light!
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Solar Cycle
• Increase in solar wind activity- Coronal Mass Ejections
• Increase in Auroral displays on Earth• Increase in disruptions on and around
Earth.
Courtesy of SOHO/LASCO/EIT consortium.
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Sunspots
• 11-year sunspot cycle.• Center – Umbra: 4500 K• Edge – Penumbra: 5500 K• Photosphere: 5800 K
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Magnetic fields and Sunspots
• Where magnetic fields “pop out” of Sun, form sunspots.
• Sunspots come in pairs.