SCI238 Lecture Notes - Neutrino, Solar Maximum, Solar Minimum
9 Jul 2013
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Document Summary
Nuclear fusion requires extremely high temperatures and densities. Recall that our sun was born about 41 billion years ago from a collapsing cloud of interstellar gas. The contraction of the cloud released gravitational potential energy, raising the interior temperature and pressure. With- out another source of energy to replace the energy output from its surface, the sun continued to contract until its central temperature finally rose high enough to sustain nuclear fusion. Sun was finally able to replace the energy lost from the surface and stopped contracting. 2 kinds of balance to make sun stable: gravitational equilibrium (or hydrostatic equilibrium), is between the outward push of internal gas pressure and the inward pull of gravity. A stack of acrobats provides a simple example of gravitational equilibrium. The sun"s internal pressure precisely balances gravity at every point within it, thereby keeping the sun stable in size the pressure must increase with depth.
