The Sun's Fuel

The sun's energy is the source for all life on Earth. Its heat allows water to remain a liquid on our planet and sustains life as we know it. For thousands of years, scientists and philosophers have tried to understand just what process could produce this enormous energy over so many years. It is interesting to look at some early scientific ideas:

1. In the late 1700s, the philosopher Immanuel Kant calculated that if the sun generated energy chemically (such as by burning coal), it could only last for a few thousand years.

2. In the late 1800s, the German physicist Hermann von Helmholtz calculated the energy that might be generated if the sun was still contracting under gravity, and came up with an answer that the sun would only last about 20 million years.

These mechanisms then could never hope to explain the sun's energy, as we now know the sun is about four billion years old!

Early in the 20th century, the famous scientist Albert Einstein showed that if you can somehow combine two particles (such as atoms or molecules) to form a new and heavier particle, it is possible that the total mass of the new particle may be slightly less that the particles forming it, and that "leftover" mass can be converted to energy. He showed that just a little mass (m) can result in an enormous amount of energy (E), according to his famous equation:

E = m x c²

where c is the speed of light, a very large number: 186,000 miles/sec.

The process of forcing two particles together to form a new heavier particle is called nuclear fusion, and requires very high pressures and temperatures (approx. 15,000,000 degrees) for it to work. These pressures and temperatures are found in the core of the sun, where a continuous nuclear reaction is taking place. The process converts 600 million tons of hydrogen to 596 million tons of helium every second. (This is about half the weight of Mt. Everest!) The difference of four million tons is converted to energy as shown in Einstein's equation. This is sufficient to explain the energy of the sun. There is enough hydrogen on the sun for this process to continue for another five billion years.

1. Can you describe two ways that nuclear reactions take place on the Earth? (e.g. nuclear reactors, nuclear bombs)

2. Why is it very dangerous when something goes wrong at a nuclear power plant?

3. How can you make two particles fuse together to form a new heavier particle?

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