Announcements. Homework 7 due today Pick up Homework 8 Next test will be next week. Our Solar System and Others. 16 October 2006. Today:. Solar system patterns Age of the solar system (and a crash course in nuclear physics) Formation of the solar system Planets around other stars.
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16 October 2006
Age of the earth?
William Thomson, Lord Kelvin
To get an actual number, we need nuclear physics.
Each chemical element has a different number of electrons (and an equal number of protons).
Masses and rarities increase (mostly) toward the bottom of the table.
Same element, different numbers of neutrons (hence different masses).
Examples: Hydrogen-1 (1p, 0n); Hydrogen-2 (1p, 1n); Uranium-235 (92p, 143n); Uranium-238 (92p, 146n).
Of all the thousands of possible isotopes, only a few hundred are stable. These tend to have slightly more neutrons than protons. Others spontaneously decay.
Example: Potassium-40 decays to Argon-40 with a half-life of 1.4 billion years.
This is a very active field of research, and better instruments are being planned and built.
“Kepler” telescope, 2008?
“Webb” telescope, 2013?