Class Notes (837,186)
Canada (510,155)
Physics (349)
PCS 181 (141)
Lecture 7

Introduction to Astronomy-Lecture 7 Notes!.docx

4 Pages
76 Views
Unlock Document

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
More Less

Related notes for PCS 181

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit