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Sun Lecture 1. Bulk Properties Fill in Vital Statistics, except Luminosity Show the TRACE Photographs Read the description of the Sun from Warren’s Recreations in Astronomy, 1879 Define Luminosity 2. Maintenance of Solar Heat Read “On the Maintenance of Solar Heat” from Young’s Lesson’s in Astronomy, 1903 3. Energy Source of the Sun Nuclear Fusion: The Proton-Proton Chain i. 4p1He + 2 +7 ii. 7 are “thermalized” by the time they reach the surface Energy generated from Mass Loss Initial Mass of 4p: 6.6943x10-27 kg Final Mass of 1He: 6.6466x10-27 kg Mass Lost = 0.0477x10-27 kg Mass is converted into Energy through Einstein’s E=mc2 How much mass must be converted into Energy each second? E/t = mc2/t =L m/t =L /c2 = 4,3 x 109 kg/sec = 4.3 Million metric tons per second! 4. Two Layer Model of the Sun (See Interior of Sun Handout) Core Envelope Weight lifter Analogy 5. The Lifetime of the Sun How long can the Sun continue to lose mass at this rate? Personal Weight Loss Analogy Estimated Lifetime of the Sun = M/(m/t) T = 1.99x1030 kg/4.3x109 kg/sec = 4.62x1020 sec = 15 Trillion years The more correct answer is 10 Billion year lifetime, with about 5 Billion to go The Sun Vital Statistics Radius_______________ Volume______________ Mass _______________ Density _____________ Surface Temperature _________ Core Temperature ___________ Luminosity ________________ Definition of luminosity: ______________________________________ _____________________________________________________________ Source of the Sun’s Luminosity is _______________________________ Implications of the Sun’s Luminosity: The Sun produces energy by converting mass into energy. The luminosity of the Sun thus represents a continual mass loss. The Sun is currently converting 4.3 million metric tones of mass into energy each second. How long can the Sun maintain this rate of mass loss? Simple answer: ____________________________ More accurate answer: 10 Billion years. The moral of the story: The Sun has a limited lifetime because it is producing energy at the expense of its own mass. It will eventually run out of mass to convert into energy. Thus, all stars have limited lifetimes because they operate in a manner similar to the Sun. Further, the more luminous a star is the faster it converts mass into energy and the shorter its lifetime. High luminosity stars have relatively short lifetimes. Low luminosity stars have relatively long lifetimes. Earth Two Layer Model of the Sun Envelope Core Thermal Forces Gravitational Forces Property Radius Volume Mass Density Temperature Core ~Inner 20% ~1% of Solar Volume ~1/3rd of Total Mass ~100 gm/cm3 15 Million K Envelope ~Outer 80% ~99% of Solar Volume ~2/3rds of Total Mass ~1 gm/cm3 5,800 K The function of the core is to produce energy and support the envelope. The envelope’s function is to contain the core and maintain core conditions so energy can continue to be produced.