Sun Spots and Sun Age

10 July, 2011

A handle-shaped prominence emerging from the Sun.
Handle-shaped prominence – a huge cloud of relatively cool dense plasma suspended in the Sun's hot, thin corona. Emission in this spectral line shows the upper chromosphere at a temperature of about 60,000 degrees Kelvin. The hottest areas appear almost white, while the darker red areas indicate cooler temperatures.
Image: Extreme Ultraviolet Imaging Telescope (EIT)
Source: ESA/NASA/SOHO

Question: Can sun spots be used to predict the past, current and/or future life cycle stage of our Sun, or indeed any star?

Answer: An interesting question, and one that we have very little evidence to go on. 

We do know that our Sun goes through an eleven-year cycle of sun spot activity. We are now just coming out of the Sun's low period and are heading into its high period. As the Sun exists for some eight to nine billion years and it is now about 4.6 billion years old, the Sun is about half way through its life cycle. The fact that we have been only observing the Sun for such a small fraction of its life means that we do not have any evidence that sun spot activity gives us any indication of its cycle. 

Observation of other stars have indeed shown they also exhibit sun spots and go through a cycle, but at the moment we do not believe they indicate the age of the star. We know the stage of our Sun's life cycle by its size and spectral emission, and this is well established.

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An ocular projection of the Sun with large sun spots using a spotting scope.

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