Kelvin–Helmholtz mechanism  From Wikipedia, the free
encyclopedia Jump to: navigation, search    However, it soon was
recognized by Sir Arthur Eddington and others that the total
amount of energy available via this mechanism only allowed for
the Sun to shine for millions of years rather than the billions
of years that the geological and biological evidence suggested
for the age of the Earth. (Kelvin himself had argued that the
earth was millions, not billions, of years old.) The true source
of the Sun's energy remained uncertain until the 1930s in which
it was shown by Hans Bethe to be nuclear fusion.  Power
generated by a Kelvin–Helmholtz contraction[edit]
Gravitational potential energy from Newtonian mechanics is
defined as:  U = -\frac{Gm_1m_2}{r}      Recasting in terms of
the mass of the sphere gives the final answer:   While uniform
density is not correct, one can get a rough order of magnitude
estimate of the expected age of our star by inserting known
values for the mass and radius of the Sun, and t