THE SUN The star we see by day
Goals Summarize the overall properties of the Sun. What are the different parts of the Sun? Where does the light we see come from? The scientific method: solar neutrinos.
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.
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)
Solar Interior Core Radiation Zone Convections Zone Only place with fusion Radiation Zone Transparent Convections Zone Boiling hot
In The Core Density = 20 x density of Iron Temperature = 15,000,000 K Hydrogen atoms fuse together. Create Helium atoms.
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 = mc2 E = (4.7 x 10-29 kg ) x (3.0 x 108 m/s)2 E = hc/l l = 4.6 x 10-14 m (gamma rays) So: 4H He + light!
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.
Solar Cross-Section Progressively smaller convection cells carry the energy towards surface. See tops of these cells as granules.
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.
The Chromosphere Hydrogen most common. Brightest hydrogen line – Ha. Chromosphere = color
Ha Sun Photo by Big Bear Solar Observatory
Prominences
Corona The hot, low density, gas at this altitude emits the radiation we see as the Corona. 1,000,000 km But corona very faint compared to photosphere.
Solar Wind At and above the corona: Gas is very hot Very energetic Like steam above our boiling pot of water, the gas ‘evaporates’. Wind passes out through Coronal Holes Solar Wind 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.
Sunspots 11-year sunspot cycle. Center – Umbra: 4500 K Edge – Penumbra: 5500 K Photosphere: 5800 K Sunspots
Magnetic fields and Sunspots At kinks, disruption in convection cells. Sunspots form.
Magnetic fields and Sunspots Where magnetic fields “pop out” of Sun, form sunspots. Sunspots come in pairs.
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.
Aurora The solar wind passes out through the Solar System. Consists of electrons, protons and other charged particles stripped from the Sun’s surface. When charged particles and magnetic fields interact: light!
2003 CME Oklahoma 10/29/2003 Credit: E. Woldt
Solar Neutrino Problem We observe: Sun’s luminosity (total light radiated). We hypothesize: 4H He + light + neutrinos We can test: Observe number neutrinos reaching Earth Does our test agree with hypothesis? No
What to Do? For 30 years: What to do? Theorists certain of nuclear reaction. Observers positive of observations. Detected only 1/3 the hypothesized neutrinos. What to do?
Neutrino Flavors 3 types of neutrinos Electron neutrino Tau neutrino Muon neutrino Nuclear reactions produce only electron neutrino. Previous detectors only detected electron neutrinos.
Neutrino Fluctuations New detector (2002) gives number of all three flavors. Total number agrees with number predicted in core of Sun. Conclusion: Nuclear hypothesis is correct. Neutrinos change flavor. Neutrinos have mass (used to be thought massless). Problem solved new science discovered.
Homework #6 Due Tuesday 2/3 Read Exoplanet articles. (Homework is to read the articles and website.) Website is: http://www.howstuffworks.com/planet-hunting2.htm