10.1 A Closer Look at the Sun
Gravitational Contraction The Sun generates energy by slowly contracting in
• Gravitational contraction provided the energy that heated the core of the Sun as
the Sun was forming.
• Gravitational contraction stopped when fusion began.
Fusion The fusion of hydrogen into helium is how the Sun produces energy to
keep its temperature and pressure high enough to resist gravity.
• The Sun is powered by NUCLEAR ENERGY, so the Sun shines.
Gravitational Equilibrium The outward push of pressure balances the inward pull
• Weight of upper layers of Sun compresses lower layers; high density and high