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Szydagis04.13.2015 1 / 14 NASA/STEREO/SDO/GSFC

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1. How do we know that the sun is a star (and bonus: when and how did we learn this in history? Note I mentioned this in class, but it was a long time ago) This is basically a review of all properties of a star 2. What color is the sun? (Interpret color how you wish.) Explain the answer fully (not 1-word answer :) 3. By what means do we know how far the sun is? 2 / 14 Activities

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The sun is a yellow, G-class star on main sequence Can actually be called a yellow dwarf, but informally As all stars, nearly spherical, and fuses hydrogen into helium in its core as means of balancing out gravity 4.567 billion years old, so about halfway through life Over 100x the earths diameter, but over 300,000x the mass. Accounts for 99.86% of mass of solar system Mean density works out to 1.4 g/cm 3, slightly >water Ball of plasma (a gas hot enough to be composed primarily of ions instead of atoms. Electrons stripped!) Temperature (surface) ~5,500-6,000 K/C (10 4 F) Our Sun: Facts 3 / 14

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Earth is 1 A.U., 149.6 million km, away (93 million mi.), while sun 27,200 light years from galactic center Orbits elliptically once per 365.256 days (sidereal year) Light travel time of 8 minutes, 19 seconds in vacuum Moving around the galaxy (once every 2-250 million years) while earth and rest of planets move around it 220 km/s relative to black hole at center of the galaxy 20 km/s relative to mean speed of the closest stars 370 km/s relative to Cosmic Microwave Background Completes own full rotation once every ~25-35 days Helioseismology : bell-like ringing turbulence ( sunquakes? ) Distance and Motion 4 / 14

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Kelvinsong (Wikipedia user) http://www.seas.columbia.ed u/~ah297/un-esa/sun/sun- chapter1.html Solar Cut- away 5 / 14

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What particle did we think we were missing many of from the sun until we understood their nature better? A. Neutrino B. X-ray C. Gamma-ray D. Nucleon The most common EM emission from the sun is A. Light (visible) B. Microwaves C. Heat (infrared) D. Ultraviolet Questions CHALLENGE 6 / 14

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Absolute magnitude of 4.83 (so, at the same distance from earth that Vega is, 25 light-years away, sun would be quite faint. ~5-6 is the limit of naked eye) 3.8 x 10 26 W(atts). Relative magnitude in sky of -26.7 Even though looks yellow, that is only because that is peak in emission. It produces light at all visible wavelengths (called white light) + below/beyond Atmospheric effects (refraction, optical depth, angle), plus psychology, change apparent size or color Reddens at sunrise, sunset. More air: scatters blue Prismatic differential angle of refraction/scatter leads to the famous sunset green flash (is real, but NASA images in the UV for instance employ false colors) Visual Appearance 7 / 14

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Blackbody Spectrum Graph courtesy of Berkeley Lab Heat Island Group 8 / 14

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The solar wind causes high- energy, electrically-charged particles to bombard earths atmosphere all the time Planetary magnetic field leads to spiraling paths around (magnetic) poles Aurora borealis in north, australis in south (is same) Color: from e - energy levels Also: coronal mass ejection, a massive burst of magnetic gas carried on solar wind EM Phenomena While docked and onboard the International Space Station on March 21st 2008, an STS-123 Endeavour crewmember, looking northward across the Gulf of Alaska, captured the glowing green beauty of the Aurora Borealis over the Earth An artist's conception of what an aurora would look like from space 9 / 14 Yellowish- green= oxygen

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The sun has an 11-year cycle in sunspot activity (periodic) Magnetic field oscillations Controversially linked to global warming, as opposed to human activities (CO 2 ) Solar maximum was in 2013 BUT weakest in >century CMEs, solar flares can also have effects: aurora; disrupt communication, electronics An Effect on Our Weather This image was created by Robert A. Rohde from the published data listed below and replaces an image created by William M. Connolley. It is part of the Global Warming Art project. Leland McInnes 11 / 14

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Recall that when two protons fuse to form a larger nucleus, one of them is forced to decay: neutron, e +, neutrino From pp, other processes (Boron-8, etc.) a certain number of neutrinos expected (predicted) from our Sun But, fewer: only one-third observed! A mystery for decades, with particle physicists accusing the astronomers of not having the correct solar model Correct answer only achieved after realizing neutrinos oscillate in flavor There are 3 types, but also 3 masses Solar Neutrino Problem Homestake Solar Neutrino Experiment 4,850 depth (4,300 m.w.e. or meters of water equivalent) at the S anford U nderground R esearch F acility (SURF) in Lead in South Dakota, the site (back then) of the Homestake gold mine. Noble Prize winning results. (LUX detector is installed in the Ray Davis cavern!) 12 / 14

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A. Red supergiant, then supernova B. Red supergiant, then black hole C. Red giant, then neutron star D. Red giant, then white dwarf A. Nitrogen B. Helium C. Iron D. Oxygen Future Fate = ? Sequence of events brought on by the beginning of the burning of 13 / 14

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Homework #10 passed out (again) now due Monday NASA Probe Captures Images of Pluto and Its Moon Charon http://www.scientificamerican.com/article/nasa-probe- captures-images-of-pluto-and-its-moon-charon-video/ http://www.scientificamerican.com/article/nasa-probe- captures-images-of-pluto-and-its-moon-charon-video/ New Horizons spacecraft set to make first flyby of Pluto in July Dawn spacecraft gets an eyeful of dwarf planet Ceres http://www.bbc.com/news/science-environment-30888818 http://www.bbc.com/news/science-environment-30888818 Both to be read by this coming Monday also please Homework 14 / 14