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How much energy does the sun produce?

Q: How much energy does the sun produce and where does it all come from and what makes it so stable?
CS, Newton

A: The sun is an average star. It is composed of a large spinning sphere of very hot gas and plasma. The sun has no surface in the conventional sense. It just gets more and more dense as you move in. By our standards, the sun is huge and that is what gives it its great stability. However, it is not as stable as you might think.

The sun radiates uniformly in all directions, mainly visible light and infrared radiation, and we can calculate the total amount of energy radiated by measuring the quantity of solar energy/second reaching every square meter of Earth and then multiplying that by the total surface area of a sphere with radius equal to the radius of Earth orbit. We get the astonishingly huge amount of 400 trillion trillion watts. To put this into a crazy context, every second the sun produces the same energy as about a trillion 1 megaton bombs! In one second, our sun produces enough energy for almost 500,000 years of the current needs of our so-called civilization. If only we could collect it all and use it!

Where does this prodigious amount of energy come from? The answer is very simple. The nuclear fusion process that takes place in the central region of the sun converts hydrogen into helium plus energy. One thousand grams of hydrogen produces 993 grams of helium with 7 grams of mass being converted into energy via E=mc2.

The sun formed from a massive cloud of gas about 5 billion years ago. It took about 50 million years to form. When it was a newborn star, it had enough hydrogen fuel for 10 billion years. It has now used up about half of its useful hydrogen reserve, and during this time the energy per second output of the sun has increased by almost a factor of 2. The sun has about another 5 billion years to go, and it will increase by another factor of about 2. When the useful hydrogen is all used up, the sun is doomed and will take about 200 million years to very slowly die.

Dr. Knowledge answers your questions about health and science each week. E-mail questions to drknowledge@globe.com, send a fax to 617-929-9263, or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819. Include your initials and hometown.

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