Lecture 4 - Orbital Mechanics (1/21/99)

Blackbody --- | --- Binaries

Reading:

Chapter 1, 12-1 (ZG4)


Notes:

pages 12 - 16

	Key Question:	What can we learn from binary stars?
	Key Principle:	Newton's Laws of Gravitation
	Key Problem:	What determines the relative orbit of a 2-body system?

Investigations:

1. Weighing the Stars
   • When did William Herschel discover that the Castor system was a binary star?
   • What percentage of stars in the solar neighborhood are members of multiple star systems?
   • Why are apparent doubles not considered real binary stars?
   • How are binary stars used to determine stellar masses?
   • How are the luminosity and temperature of stars measured?
   • What are the four primary physical parameters of stars?
   • What is a visual binary?
   • What is a spectrum binary?
   • Why are spectroscopic binaries useful?
   • What can we learn from eclipsing binary systems?
2. Orbital Mechanics Revisited
   • Kepler's 1st Law states that orbits are ellipses with the Sun at one focus. How does this apply to binary stars?
   • What is the eccentricity of an ellipse?
   • What is the center of mass?
   • What is the reduced mass and what is its role in the center of mass coordinates?
   • What is the energy equation for a binary system?
   • What is the angular momentum equation?

Review of Mechanics:

For a review of orbital mechanics, especially Kepler's Laws and Newton's Laws, see Chapter 1 in ZGS (especially 1-2 through 1-4). Also, look at the Astro 11 lectures

• Lecture 4 - Newton's Mechanics
• Lecture 5 - Orbital Mechanics I
• Lecture 6 - Orbital Mechanics II
• Lecture 7 - Orbital Mechanics III

Note that we will be using mechanics all through the semester so it is worth spending time now to really get into it. In particular, we will be studying the motions of stars in our galaxy, galaxies in clusters of galaxies, and the dynamics of the Universe as a whole which will build on these fundamental ideas!

For those of you who did not take Astro 11, you can review these subjects in the above-mentioned chapters of the textbook, or look at my lecture notes placed on reserve in the Math-Physics library on the 3rd floor of DRL.

Prev Lecture --- Next Lecture --- Astr12 Index --- Astr12 Home

smyers@nrao.edu Steven T. Myers