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Mercury, Sep/Oct 2001 Table of Contents

Courtesy of SOHO/The EIT Consortium/ESA/NASA.

After nearly two centuries of debate, recent neutrino experiments have solidified our understanding of solar energy production.

by John Bahcall

What makes the Sun shine? How does the Sun produce the vast amount of energy necessary to support life on Earth? These questions challenged scientists for 150 years, beginning in the middle of the 19th century. Theoretical physicists battled geologists and evolutionary biologists in a heated controversy over who had the correct answer.

The questions "How old is the Sun?" and "How does the Sun shine?" are actually two sides of the same coin. We can easily compute the rate at which the Sun radiates energy by measuring the rate at which energy reaches Earth’s surface and factoring the distance between the Sun and Earth. The total energy that the Sun has radiated over its lifetime is approximately the product of the current rate of energy emission, which is called the solar luminosity, times the age of the Sun. The greater the radiated energy, or the older the age of the Sun, the more difficult it is to explain the Sun’s source of energy.