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However, the amount of sunlight that Earth receives is only a fraction, 1/2.2 billionth to be exact, of the total radiation energy emitted by the Sun. To put the Sun’s power into perspective, imagine if there were a 12-meter-thick layer of ice covering its surface – in just one minute, the Sun’s heat would melt that entire layer of ice. What’s even more astonishing is that the Sun has been emitting light like this for billions of years.
For a long time, people have wondered: Where does this immense energy of the Sun come from?
Certainly, the Sun isn’t burning like a conventional fire, because even with the highest-quality oxygen and coal, having a mass equal to that of the Sun, the burning process could only sustain luminosity for around 2500 years. However, the Sun’s lifespan spans billions of years, much longer than that.
In 1854, German scientist Kaimuhop proposed the first scientific theory about the Sun’s energy source. He suggested that the gases on the Sun continuously emit heat, causing the Sun to cool down and contract. These contracting materials then fall back onto the Sun, generating energy to replenish the lost energy. Based on calculations, if the Sun’s diameter were to decrease by 100 meters annually, the energy released from this contraction would compensate for the radiated energy. Unfortunately, even if the Sun’s initial diameter matched the orbit of the farthest planet in the Solar System, its contraction could only sustain its luminosity for about 20 million years.
During the 19th century, some scientists proposed that the Sun’s light emission was due to the impact of meteorites falling onto the Sun, resulting in heat generation through chemical reactions, decay of radioactive elements, and more. However, all of these factors couldn’t account for the release of the massive and enduring energy the Sun emits.
In 1938, the discovery of atomic nuclear reactions finally solved the puzzle of the Sun’s energy source. The Sun’s colossal energy emission is attributed to its atomic nuclear reactions. The Sun is primarily composed of hydrogen atoms. In the Sun’s core, under conditions of extreme temperature (15 million°C) and pressure, hydrogen atomic nuclei interact and combine with helium atomic nuclei, releasing both light and limitless heat.
Hence, the Sun’s heat-generating process is not a conventional phenomenon as we may have thought. Within the Sun, nuclear fusion reactions of hydrogen into helium generate immense energy. On the Sun’s surface, there is an abundant supply of hydrogen participating in these nuclear fusion reactions, which can provide the Sun with the ability to shine and produce heat for another 5 billion years.
In the future, even if all the hydrogen on the Sun gets consumed, there are still nuclear fusion reactions involving other elements, allowing the Sun to continue emitting light and heat indefinitely.