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Transcript
THE SUN The star we see by day 7 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. 7 Interior Properties • Core = 20 x density of iron • Surface = 10,000 x less dense than air • Average density = Jupiter • Core = 15,000,000 K • Surface = 5800 K 7 Scientific Method • How do we know this stuff? • Three examples: – Fusion in the core (core temperature). – Different zones in interior. – Solar activity and Earth 7 1. The Core • Scientific Method: – Observations – Make hypothesis (a model) • Models make predictions – Test predictions • Compare results of predictions with observations – Revise model if necessary. 7 Testing the Core • Observe Sun’s: – Mass (how?) – Composition (how?) – Radius • Use physics to make a model Sun. • Predict: – Surface temp/density (how do you test?) – Surface Luminosity (how do you test?) – Core temp/density Fusion Rate neutrino rate (test?) 7 In The Core • Density = 20 x density of Iron • Temperature = 15,000,000 K • Hydrogen atoms fuse together. • Create Helium atoms. 7 2. Helioseismology • Continuous monitoring of Sun. – Ground based observatories – One spacecraft (SOHO) • Surface of the Sun is ‘ringing’ • Sound waves cross the the solar interior and reflect off of the surface (photosphere). 7 Solar Interior • Core – Only place with fusion • Radiation Zone – Transparent • Convections Zone – Boiling hot 7 Convection • • • • A pot of boiling water: Hot material rises. Cooler material sinks. The energy from the pot’s hot bottom is physically carried by the convection cells in the water to the surface. • Same for the Sun. 7 Solar Cross-Section • Progressively smaller convection cells carry the energy towards surface. • See tops of these cells as granules. 7 The Photosphere • This is the origin of the 5,800 K thermal radiation we see. l = k/T = k/(5800 K) l = 480 nm (visible light) • This is the light we see. • That’s why we see this as the surface. 7 3. Solar Activity and Earth • Is there a connection between Solar Activity and Earth’s Climate? • Observation: – Little Ice Age – Maunder Minimum 7 What is Solar Activity? • • • • • • • Sunspots Magnetic Fields Coronal Mass Ejections Solar Wind Magnetic Storms Aurora Other effects? 7 • • • • 11-year sunspot cycle. Center – Umbra: 4500 K Edge – Penumbra: 5500 K Photosphere: 5800 K Sunspots 7 Magnetic fields and Sunspots • At kinks, disruption in convection cells. • Sunspots form. 7 Magnetic fields and Sunspots • Where magnetic fields “pop out” of Sun, form sunspots. • Sunspots come in pairs. 7 Prominences Hot low density gas = emission lines 7 7 Corona and Solar Wind • Hot, low density, gas emits the radiation we see as the Corona: 1,000,000 K • Solar Wind: Like steam above our boiling pot of water, the gas ‘evaporates’. • Carries away a million tons of Sun’s mass each second! • Only 0.1% of total Sun’s mass in last 4.6 billion years. 7 7 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. 7 Aurora • The solar wind passes out through the Solar System. • Consists of electrons, protons and other charged particles stripped from the Sun’s surface. • Magnetic fields herd charged particles into atmosphere at poles. • Charged particles excite electrons in atoms. Light! 7 7 7 2003 CME Oklahoma 10/29/2003 Credit: E. Woldt 7 Homework #7 • Due Monday 30-Jan, Read Exoplanet articles plus the website: • http://www.howstuffworks.com/planethunting2.htm Why do we believe there are planets around other stars? How have we detected them? 7