The Nearest Star

A very average sort of star Normal, Quiet Sun Features of Activity cycle Solar energy
   Sun has been around for 4.5 billion years. What could produce
   such prodigious quantities of energy?
   
   Chemical energy: coal/oxygen would last ~5,000 years
 
   Kelvin-Helmholtz (gravitational) contraction
      energy goes about half to temperature, half to light
      need contraction of about 120 feet/year
      could go about 50 million years
 
   thermonuclear fusion