http://www.my-maverick-moneymakers.com/solar-energy-wikipedia/
What is age of solar system?
Before people realized that E = mc², and stuff,
the source of solar energy was a puzzle.
Assuming that all energy radiated by the Sun
comes from its contraction under its own gravity,
estimate the age of solar system.
Physical properties of the Sun are listed here:
http://en.wikipedia.org/wiki/Sun
Calculate the gravitational self-energy of a sphere of solar mass and radius. Assume uniform density (not correct, but good enough for a first order approximation).
ie integrate G (density)^2 (volume of a sphere of radius r) (volume of a shell of radius r and width dr) / r — from r equals zero to the sun’s radius
Divide that by the power radiated by the sun to get a time.
The time isn’t very long–a very perplexing problem before they figured out solar fusion.
Astounding FOOTAGE!!! Functional Do It Yourself Homemade Solar Energy
