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Download Finish up Sun and begin Stars of the Sun Test 1 Study
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PHYS 162 1 Sunspots • Intense magnetic fields which inhibited convection currents to the surface appear darker as at lower temperature • Solar storms/flares often associated with sunspots • Had been observed prior to Galileo’s time (and without telescopes) – Galileo gets credit as he had best explanation • Sunspot activity varies with time. 11 year cycle plus variation over hundreds (thousands) of years – change in Solar energy output PHYS 162 2 Outer Atmosphere • Can see during eclipses. Interactions of solar wind with Earth’s magnetic field and atmosphere causes Aurora Borealis PHYS 162 3 Solar Storms • Large eruptions from Sun’s surface are called “flares” or “storms” • Will increase flow of charged particles to Earth, increase Northern Lights, and have (some) radiation impact (plane flights, on space station, radio signals) • Large one in January 2012 PHYS 162 4 Aurora Borealis – Northern Lights seen at high latitudes as magnetic fields are lower in the atmosphere. rarely seen in DeKalb. Photos are from Alaska and Maine PHYS 162 5 Test 1 Guide for short answer questions • Motion of Sun, stars, and planets through sky vs season • Galileo’s astronomical observations • Kepler’s Laws of planetary motion • Newton’s Laws of motion (mostly F=ma) • how light is produced (accelerated charge) plus discrete vs. continuous • nuclear reactions in the Sun : p-p cycle • Layers in the Sun • 4 forces with examples PHYS 162 6 The Nature of Stars • Measure properties of Stars Distance Mass Absolute Brightness Surface Temperature Radius • Find that some are related Large Mass Large Brightness • Gives model of stellar formation and life cycle PHYS 162 7 Distances to Stars • Important as determines actual brightness but hard to measure as stars are so far away Closest Alpha Centauri 4.3 light years = 4 x 1013 km (1 AU = distance Earth to Sun = 8 light minutes) • Close stars use stellar parallax (heliocentric parallax or triangulation same meaning) • Can “easily” measure distance using parallax to a few 100 LY. Need telescope: first observed in 1838. Study close stars in detail. Other techniques (later) for distant stars PHYS 162 8 Distances to Stars - Parallax PHYS 162 9 Shifting Star Positions • • • • The orbit of the earth is used as the base. Near stars appear to move more than far stars distance = (base length)/angle define: 1 parsec = 1/(angle of 1 second of arc) = 3.3 LY site A December angle Sun site B June PHYS 162 10 Stellar Parallax • A photo of the stars will show the shift. July PHYS 162 11 Nearest Stars 61 Cygni first parallax in 1838 Alpha Centauri Sirius Procyon 61 Cygni Epsilon Indi All binaries Tau Ceti 12 LY closest single “Sunlike” star Epsilon Eridani single - youngish PHYS 162 12 Nearest Stars •The larger the angle (T.Par. = trigonometric parallax) the closer the star • many stars come in groups like the 2 stars in the Sirius “binary cluster” close together, within same “solar system” •Alpha Centauri and Procyon are close binary systems. Proxima Centauri is a red dwarf which probably orbits Alpha Centauri every 500,000 years PHYS 162 13 Nearest Stars 61 Cygni first parallax in 1838 PHYS 162 14 Parallax Data • In 1900 only 60 stars had parallax measurements • 1997-2000 a European satellite Hipparcos released parallax measurements for more than 2,300,000 stars up to 500 LY distance • 118,000 stars measured with .001 arc-second resolution and 0.2% error on light intensity • OLD(1990): 100 stars with distance known to 5%. “NEW” (2005): 7000 such stars • ESA Gaia satellite: 2013 0.00001 arc-second. Goal: measure 1 billion objects ~70 times each over 5 years PHYS 162 15 Luminosity of Stars • Luminosity=Absolute Brightness=how much light/energy a star produces • Scale relative to Sun. So Lsirius = 23LS means Sirius radiates 23 times more energy than the Sun • Stars range from .0001xLS to 1,000,000xLS Another scale: “magnitude” often used. A log scale to the power of ~2.5. YOU DON’T NEED TO KNOW. The lower the Mag the brighter the object PHYS 162 16 Absolute vs Apparent Brightness Absolute Brightness/Luminosity means total energy output Apparent Brightness is what is seen by eye or in a telescope and so depends on distance (1/Distance2) PHYS 162 17 Absolute vs Apparent Brightness Example: 2 stars with the same absolute brightness Star(A) is 3 times further away from us then Star(B) therefore the apparent brightness of Star(A) is 1/9 that of Star(B) 90 LY 30 LY PHYS 162 18 apparent brightness what we see magnitude scale close to us far away but very large Absolute brightness PHYS 162 19 Brightness: Sirius vs Rigel • Sirius is 23 times as bright as our Sun Rigel is 30,000 times as bright as our Sun • Sirius is 8.6 light years from us Rigel is 30,000 light years from us • Which star looks brighter in the sky? Has the larger apparent luminosity? Sirius Sirius : Rigel : 23 23 0.3 2 8.6 74 30000 30000 0.07 2 680 460000 PHYS 162 20 Binary Star Systems • Many stars come in groups of 2 or 3 that are close (few AU) to each other: BINARY Star Systems • Gravitationally bound and probably formed at the same time • SiriusA is 23 times as bright as our Sun SiriusB is 0.005 times as bright as the Sun Their separation varies from 8 to 31 AU PHYS 162 21 Binary Stars Stellar Masses • visually observe both stars Visual Binary. If only separate into 2 stars by looking at the spectrum Spectroscopic Binary (eclipse each other plus have different Doppler shifts) • Measure orbital information period and separation distance. Get Mass though Kepler/Newtonian-like methods PHYS 162 22 Binary Star Orbits - Eclipses PHYS 162 23 Binary Star Orbits – Doppler Shifts PHYS 162 24 Extra Slides PHYS 162 25 Weak Nuclear Force • Affects all particles (except photon) • Weaker than electromagnetic force except at high energies where the same strength • Short range - size of proton • Causes changes in particle type. Many radioactive decays are “weak” and so can occur slowly proton neutron electron neutrino particle PHYS 162 antiparticle 26 Neutrinos - little neutral ones • Postulated to exist in 1930s, discovered in 1956 (second type discovered in 1962). Neutrinos (n) have: almost 0 mass and no electric charge unaffected by strong nuclear force only interact by weak nuclear force • only 1 of 1010 produced in the Sun’s interior interact in Sun’s outer layers can be used to study Sun’s interior Sun n PHYS 162 Earth detector >1000 tons of water 27