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Lecture 7

# Introduction to Astronomy-Lecture 7 Notes!.docx

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School
Department
Physics
Course
PCS 181
Professor
Margaret Buckby
Semester
Winter

Description
 75% Hydrogen, 24% Helium, 1% everything else.  The Main Sequence Stage: 6  T Core 10 x 10 K =  Hydrogen fusion nuclear reactions in the core.  A star spends its life in a delicate balance between outward radiation pressure and inward gravitational pull.  ~90% ~95% of stars are Main Sequence…  Including our sun. Hydrogen Fusion Reactions= Proton-Proton Chain: 1 1 2 +  H + H = H + e + V(deuterium, position, neutrino).  2H = H= He + V (helium, istotope, radiation burst). 3 3 4 1 1  He = He = He + H + H (helium, hydrogen).  *NOTE: FILL IN THE MISSING BLANKS FOR THE ABOVE EQUATIONS ON TEST # 2!  Strong force – nuclear force – 2 particles with in 1015m together. Dominant nuclear reactions that take place in 90-95% stars  Note that four Hydrogen nuclei fuse to form one Helium nucleus and …  A small amount of mass is released as energy.  (4.3 x 10 -12J).  Not much energy produced…  But…a typical star has 10 such reactions each second!  Therefore, the energy produced each second is  (4.3 x 10 J) (1 x 10 ) = ~ 4 x10 w.6  This is the Luminosity (energy per second) observed for our sun (a typical star).  Luminosity = L = 4 (3.14) R (SIGMA SIGN) T = energy/s. Life on the Main Sequence:  A “Main Sequence” star fuses Hydrogen nuclei into Helium nuclei deep in its core via p- p chain(=proton-proton chain). 6  Core temperature must be at least 10 x 10 K = 10 million K. REMEMBER THIS FOR TEST  4 H = 1He  ~10 38 such reactions occur each second.  Massive stars: greater core densities and greater core pressures.  Faster rate of Hydrogen fusion=  Shorter Main Sequence lifetime of only a few Million years.  Average, normal stars (like our sun) will fuse Hydrogen over lifetime of several billion years.  90% - 95% of stars are Main Sequence stars. ASK THIS ON TEST The Sun:  Massive stars only live for a few million years.  Normal stars live for billions of years.  Our Sun, a normal star, will fuse Hydrogen in its core for a total of ~10 billion years.  Our sun is now 4.5 billion years old. Nemesis:  ~55% of stars have a companion.  *NOTE: ON TESTS # 2 QUESTION: WHAT IS ANOTHER NAME FOR NEMESIS!  Mass extinctions occur on Earth ~every 25=30 million years.  Perhaps the sun has a never-observed companion which comes near to the sun periodically.  It disturbs the orbits of nearby comets, asteroids, meteors.  These may crash into Earth and precipitate mass extinctions. Characteristics of Nemesis:  If it exists.  Mass ~0.01 M o.  Distance ~ 89 x 10 AU ~ 90,000 Astronomical Unit.  WHAT DOES NEMESIS MEAN? SOMETHING THAT CAUSES MISERY, PAYBACK. IN CASE: ON TEST  Period ~26 million = 30 million years. The Red Gi
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