Transcript: Physicists in the nineteenth century made various estimates of the age of the Sun, but they were fundamentally unaware of the most efficient energy source known. Early in the twentieth century physicists Rutherford and Becquerel began a systematic study of the phenomenon of...

Transcript: Chemical energy cannot power the Sun, so what is the energy source? Inspired by an idea by the German physicist Hermann von Helmholtz the English physicist Lord Kelvin explored the idea of gravitational contraction. In this mechanism the Sun is slowly shrinking and gravitational...

Transcript: Above the solar chromosphere is the corona, a diffuse outer layer of gas at the amazing temperature of two million degrees Kelvin. Both the chromosphere and the corona have higher temperatures than the photosphere. How can this be? One way for gas to become hot is pressure. Higher...