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Last Post 10/6/2009 2:06 PM by Terry Kucera

Sun's Age

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10/6/2009 12:36 PM
Why is it that people say that the sun gets brighter every year and yet, it's 4.5 billion years old? Rachel R. Pitman

Terry Kucera

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10/6/2009 2:06 PM
Hi Rachel, I would not say that the Sun gets brighter every year. The total brightness goes up and down a little. In particular, it goes up during the maximum of the solar activity cycle. This seems a bit strange because that is the time when there are the most dark sunspots! But there are also other bright areas that increase during solar maximum and it turns out they make up the difference.These variations are very small, though - only about 0.1% Here is a plot: http://sohowww.nascom.nas...hotshots/1999_12_20/ Over the very long term, hundreds of millions and billions of years, stellar modelers do think that the Sun and other "middle aged" stars do increase in brightness, but that is a very long term effect, not one we would measure in our lifetimes. Hope that helps with your question, Terry