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However, the amount of sunlight Earth receives is only about 1/2.2 billionth of the Sun’s total radiated energy. To illustrate the Sun’s power, consider this: if there were a 12-meter-thick layer of ice covering the Sun’s surface, it would melt entirely from the Sun’s heat in just a minute. What’s even more astounding is that the Sun has been shining like this for billions of years.
For a long time, people have wondered: where does the immense energy of the Sun come from?
Certainly, the Sun is not burning in the conventional sense, because even if the highest quality oxygen and carbon were available in a mass equal to that of the Sun, it could only sustain its brightness for 2,500 years. Yet, the Sun’s lifespan extends far beyond that, potentially lasting billions of years.
In 1854, the German scientist Kaimuhop first proposed a scientific theory about the source of the Sun’s energy. He theorized that the gases on the Sun constantly emit heat, causing them to cool and contract. These contracting substances then fall back into the Sun, generating the energy needed to compensate for the lost radiated energy. Based on calculations, if the Sun’s diameter were to decrease by 100 meters each year, the energy produced by this contraction would be sufficient to offset the radiated energy. Unfortunately, even if the Sun’s initial diameter were equal to the farthest orbit of a planet in the solar system, the contraction would only sustain the Sun’s luminosity for 20 million years.
In the 19th century, some scientists believed that the Sun’s illumination resulted from cosmic dust falling onto the Sun, generating heat, or chemical reactions and the decay of radioactive elements, and so on. However, none of these could release the colossal amount of energy required for the Sun to emit such large and enduring energy.
In 1938, the discovery of atomic nuclear reactions finally unraveled the mystery of the Sun’s energy source. The Sun’s immense energy emission is a result of atomic nuclear reactions within its core. The Sun contains a large amount of hydrogen. At its core, under high temperature (15 million°C) and pressure, atomic nuclei of hydrogen interact and combine with atomic nuclei of helium, releasing both light and boundless heat in the process.
Thus, the Sun’s process of emitting heat is not as common as previously thought. In the Sun, the nuclear fusion reactions of hydrogen into helium generate the most significant energy. The Sun’s core is rich in hydrogen for these nuclear fusion reactions, which can supply the Sun with the capacity to continue radiating light and heat for another 5 billion years.
In the future, even if all the hydrogen on the Sun is depleted, there are other nuclear fusion reactions involving different elements, enabling the Sun to shine and emit heat indefinitely.