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A s t r o n o m y P h y s 1 8 1 This Lecture Brought to You in Comic Sans MS “With equal passion I have sought knowledge. I have wished to understand the hearts of [people]. I have wished to know why the stars shine.” -Bertrand Russell Quotes "One of the most impressive discoveries was the origin of the energy of the stars. One of the men who discovered this was out with his girl friend the night after he realized that nuclear reactions must be going on in the stars in order to make them shine. She said "Look at how pretty the stars shine!" He said, "Yes, and right now I am the only man in the world who knows why they shine." She merely laughed at him. Well, it is sad to be alone, but that is the way it is in this world.“ - Richard Feynman, "The Feynman Lectures“ “A star shines on the hour of our meeting.” - Elvish greeting, "The Lord of the Rings“ “I wonder why. I wonder why. I wonder why I wonder. I wonder why I wonder why I wonder.” - Richard Feynman Readings: ASTRONOMY TODAY Chapter 16 (excepting section 16.6) Chapter 17 (without exception) R e a d General Solar Properties Solar Properties Percentage of Solar System Mass Maximum Earth Distance (Km) 152,100,000 Minimum Earth Distance (Km) 147,100,000 Mean Distance from Earth (Km) 149,597,892 Earth Masses 333,400 Mass x10(30) (Kg) 1.99 Diameter of Photosphere (Earth = 1) 109.3 Diameter of Photosphere (Km) Sol ar Pro pert ies 99.80 1,390,000 Mean Density (g/cm(3)) 1.41 Solar Constant (W/m(2)) 1370 Luminosity x10(26) Watts 3.8 Spectral Class G2 V Effective Temperature (Kelvin) 5800 Apparent Magnitude -26.7 Absolute Magnitude 4.8 Rotational Period at Equator 24d16h Rotational Period at 40° 28d Rotational Period at 80° 36d Inclination to Equator to Elliptic 7°10'.5 Surface Gravity (Earth=1) 27.9 Surface Gravity m/s(2) 273 Average Sunspot Maxima (Yr.) 11.1 Average Magnetic Cycle (Yr.) 22.2 Average Escape Time for Photons Orgininating in the Core (Yr.) 10,000 W h Why does the sun shine? y d •Chemical Burning – insufficient radiation o •Radiative Cooling – only thousands of years e •Gravitational Contraction – only 25 million years s t h e E = m c Stars convert energy into matter. P r o t o n P r 600 million tons of H -> 598 million tons of IN ONE SECOND He Basic Solar Structure R a d i a t i o n The force of gravity inward and the radiation pressure outward balance each other out. Gravitational Equilibrium Spectroscopy Visible Spectrum Sp ect ros co 91.2% Hydrogen – 8.7% Helium 0.1% Heavier Elements Luminosity The total power output of the sun: 3.8x1024 watts!!! Think of your 60 watt light bulb. 1 second of the earth luminosity contains enough energy to meet our needs for roughly 500,000 years! Only about one two-billionth of that reaches Earth. L u m i n Sun Spots Not at all dark Roughly the size of the earth Show the differences in rotation: 27 days equator – 31 days poles Only about one two-billionth of that reaches Earth. S u n S Granularity of the Solar Surface G r a n u l C o n v e c A Solar Prominence P r o m i n Solar Flare F l a Understanding the sun: s i m u l a NEXT TIME: End Measuring the Stars “Perhaps the greatest anomaly in this situation is the incredibly weak scientific case for the whole scenario of cosmic evolution. There can be no "experiments" or "observations" of stars evolving, in the very nature of the case, so it cannot be scientific, though it may be naturalistic - all based on mathematical manipulations, computer simulations, and atheistic or pantheistic philosophies.” Quotes -Henry Morris in Creation by Inflation and Quantum Fluctuation Back to Genesis 129a, August 1999. “I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.” -Richard Feynman, 1968 “I believe that a theologist looking at nontheological problems is the next guy” -Professor Scheidly, Just Now Readings: ASTRONOMY TODAY Chapter 17, 20, and 21 R e a d e a r e s t N e i g h General Solar Properties P r o x i m a Proxima Centauri S t e l l a r P a Proxima Centauri: Stellar parallax = 0.76” Distance = 1/0.76 = 1.3 pc Distance = 270,000 AU Distance = 4.3 ly o p e r m o t i o n Proper Motions of Stars… c vr d vt t p a r e n t B r i g Apparent Brightness Luminous Intensity/Distance2 A change in apparent magnitude by 5 corresponds to an increase in apparent brightness by a factor of 100. The log scale allows us to express large differences in a compact way. A p p a r e n t M a a l C l a s s i f i c C h a r a c t e r Estimating Stellar Radii… Stellar Radii Hertzsprung-Russell Diagram… H R H R H R H R M 5 5 M o v e f o r e