Summary of Key Ideas

The Sun’s Atmosphere

The Active Sun

The Sun’s Interior

WHAT DID YOU THINK?

  • What percentage of the solar system’s mass is in the Sun? The Sun contains about 99.85% of the solar system’s mass.
  • Does the Sun have a solid and liquid interior like Earth? No. The entire Sun is composed of hot gases.
  • What is the surface of the Sun like? The Sun has no solid surface. Indeed, it has no solids or liquids anywhere. The level we see, the photosphere, is composed of hot, churning gases.
  • Does the Sun rotate? If so, how fast? The Sun’s surface rotates differentially, varying between once every 35 days near its poles and once every 25 days at its equator.
  • What makes the Sun shine? Thermonuclear fusion in the Sun’s core is the source of the Sun’s energy.
  • Are matter and energy conserved? By themselves, they are not always conserved. Nuclear fusion converts matter into energy. Energy can also be converted into matter. The sum of the matter (multiplied by c2) and energy is always conserved.