Transcript Chapter 11
Note: Slide which are important and should be reviewed are marked as The Sun, a Star Astronomy 360 Notes (Physics 360/Geol 360) Dr. Swez What Is the Sun? A big, hot ball of gas The Sun and planets are shown to the same scale. The small terrestrial planets and tiny Pluto are in the box--the Earth is the blue dot near the center of the box. Note: Image Not in your Text! 1. From Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version. Created by Nick Strobel using NASA images Physical Data on the Sun Mass 2x1030 kg Radius 110 REarth Use distance and trig Luminosity 4x1026 W Watch planet orbits Use distance and value at Earth Also Stephan-Boltzmann Law Surface Temp 5800K Eq Rotation 25 days Polar Rotation 33 days Composition: 71% H, 27% He, 2% Other Wien’s Law Watch Sunspots Examine spectrum Where is the sun on this graph? From: Explorations by Thomas Arny, page 325 The Mass Luminosity Law for stars Remember the Stephan-Boltzmann Law? Look ahead to p 363-365 text A body of temperature T radiates an amount of energy each second equal to T4 per square meter. If we know the energy per square meter we can find the temperature. = 5.67 x 10-8 watts m-2 K-4 Note: Image Not in your Text! From Nick Strobel's Astronomy Notes. Go to his site at www.astrono mynotes.co m for the updated and corrected version. The Photosphere (surface of the sun we see) is about 500 kilometers thick. Remember Wien’s Law (page 103 text) Measure the body’s brightness at different wavelengths to find at which particular wavelength it is brightest. Use Wien’s law to calculate the body’s temperature. T = (3 x 106 / m) Where Does the Energy Come From? Coal - lasts a few thousand years Gravothermal Energy Gravity compresses Sun, which heats it Could last 20 million years Nuclear Fusion Energy is converted to mass (E=mc2) Could last 10 billion years Mass-Energy Conversion Energy = mass x (speed of light)2 (1kg) x (3x108m/s)2 = 1017 joules watt = 1 joule/second Annual US Energy Consumption ~1020 J The Sun fuses hydrogen into helium The mass input is greater than the mass output Some mass is converted to energy Proton-Proton Chain Hydrogen fuses into helium Summary: 6 H -> 2H + 1 He + n + 3x10-7 J Requires very hot temperatures and high pressures (above 1 million K) The solar core will burn for a total of 10 billion years (How long do we have left?) Know the full chain! Neutrinos Neutrinos are small, neutral particles They easily pass through matter Several light-years of lead can block them Therefore they are very hard to detect Neutrinos can cause nuclear change in atomic nuclei Underground detectors see a few each day Solar Neutrinos Solar neutrinos are the only direct probe of the Solar core Detectors reported ~1/3 of the expected neutrinos New results -> new physics Apparently, neutrinos oscillate between states So, the Sun produces the correct number of neutrinos for current models There is no longer a ‘Solar Neutrino problem’ What if Hydrostatic Equilibrium Failed? What if gravity exceeded gas pressure? The Sun would start to collapse The core temperature and pressure would increase The nuclear fusion rate would increase Hydrostatic equilibrium would be restored! What if gas pressure exceeded gravity? Solar Atmosphere Photosphere surface we see 5800 K contains sunspots and granulation Chromosphere cooler outer layer 4500 K contains spicules Corona very thin outer layer few million K visible during eclipse contains flares and prominances Why are sunspots dark? From The WEBSITE: http://www.kis.unifreiburg.de/~pnb/granmovtext1.html A 27 x 27 Mm2 Field Condensed into 35 minutes Granulation in the photosphere of our SUN. A time lapse movie. “The series was observed with a fast frame selection system on June 5, 1993, at the SVST (La Palma) in cooperation with G. Scharmer (Stockholm) and G. W. Simon (Sunspot); N. Hoekzema (Utrecht), W. Mühlmann (Graz), and R. Shine (Palo Alto) were involved in the data analysis. Technical data: wavelength 468 ± 5 nm; exposure time 0.014 s; rms contrast (uncorrected) between 7 and 10.6 %. The images were registered, destretched, corrected for the telescope's point spread function, and subsonically filtered after interpolation to equal time steps. “ Note: Image Not in your Text! Time lapse movies of solar granulation evolution. The movies show time lapse series of the evolution of the solar granulation, which represents the top of the Sun's convection zone. At the centers of granules hot solar gas rises and radiates its heat rapidly into space; the gas then is diverted horizontally, and sinks back into the Sun in the darker intergranular lanes. The sizes of the granules range from approx. 250 km (the limit set by the telescope and the Earth's atmosphere) to more than 2000 km, with an average diameter of 1300 km. Lifetimes of granules typically range from 8 to 15 minutes. Horizontal and vertical velocities of the gas motion are 1 to 2 km/s. Courtesy of: http://www.kis.uni-freiburg.de/~pnb/granmovtext1.html H Alpha Sunspot Images taken at Holloman Air Force Base over a 10 day period. From: http://www.sunspotcycle.com/ Sunspots are cooler dimmer regions with strong magnetic fields. Note: Image Not in your Text! Can last months Erupts over days Complete Sunspot Data from http://www.sunspotcycle.com/ Note: Image Not in your Text! How can astronomers detect magnetic fields in astronomical bodies One way would be to place a magnetometer on the sun. (Impossible!). A better way is to use the Zeeman effect; a physical process by which the magnetic field splits some of the spectral lines of a gas into more than one component. The magnetic field alters the atom’s electron orbits which in turn alter the emitted wavelength. (see page 345 text) Sun Spot Data for a Period of about 10 Years Note: Image Not in your Text! Solar Cycle #23 is in progress. The next sunspot maximum is predicted to occur in the year 2000.