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Flunking ABC's Quiz

April 9, 1999
Sometimes it doesn't pay to give a test.

The ABC website science section has a pop quiz today that asks an interesting multiple choice question: ``How much mass does the Sun convert in to energy each second?'' There are four answer buttons, and the explanation pops up when you click each one. The choices (and explanations) are:

  1. 9 pounds
    [Nope, more than that]
  2. 90 pounds
    [Try again]
  3. 9000
    [Correct. And using Einstein's ''E equals m c squared'' equation, you can see those 9,000 pounds give off a lot of energy.]
  4. 900000
    [Whoah, the sun isn't quite that hot.]

The answer they give, 9000 pounds, is wrong. Quite a bit wrong. The correct answer is 5 million tons! About 700 million tons of hydrogen are fused into helium every single second in the core of the Sun. From that, a tiny fraction is converted into energy via the equation they do correctly quote.

Even though 5 million tons sounds like a lot, it's chicken feed compared to the mass of the Sun, which is 2 thousand million million million million tons! So the Sun converts only 0.0000000000000000000025 of its mass into energy every second. At that rate, it can last for over 10 trillion years! It won't really, though. Only a small fraction of the Sun's total mass is available for conversion to energy. Still, we have a good five billion years before we need to start looking around for a better neighborhood.

I emailed ABC about the mistake on their site; I'll post more when/if I get a reply.

Want to know more about our nearest star? Check out Bill Arnett's Nine Planets: The Sun page. I also have some info about the Sun on one of my Bitesize Astronomy pages.

©2008 Phil Plait. All Rights Reserved.

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