Question

Explain how we know that the Sun’s energy is not supplied either by chemical burning, as in fires here on Earth, or by gravitational contraction (shrinking).

Answer 1

The vast amount of energy produced by the Sun over the past 4.5 billion years exceeds the amount that could be supplied by burning or shrinking of the Sun by a significant factor. Chemical burning would only last a few thousand years, whereas gravitational contraction would provide energy for only about a hundred million years. but we can confidently say the sun gets its energy from matter that is converted into energy through the fusion of hydrogen into helium.