ASTRO-110 Lecture Notes - Lecture 8: Electromagnetism, Radiography, Photosphere
18 Sep 2020
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Document Summary
The first scientific hypotheses involved chemical reactions or gravitational collapse. Chemical burning ruled out it cannot account for the sun"s luminosity. Conversion of gravitational potential energy into heat as the sun contracts would keep the sun shining for 25 million years. Geological research showed the earth is much older than that. Development of nuclear theory led to the correct answer. The sun generates energy via nuclear fusion reactions. Hydrogen is converted to helium in the sun"s core. The mass lost in this conversion is transformed into energy. The amount of energy is given by einstein"s equation: e=mc2. Given the sun"s mass, this will provide enough energy for the sun. Striking a balance to shine for 10 billion years. The sun began as a cloud of gas undergoing gravitational collapse. This caused the core of the sun to get hot & dense enough to start nuclear fusion reactions. Once begun, the fusion reactions generated energy which provided an outward pressure.
