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Astronomy: Focusing on the Sun

6-17-11 Sunspots by Chumack
Two sunspots, looking like a pair of moles, appear on the solar limb. Credit: John Chumack

Summer arrives in the northern hemisphere with the solstice on June 21 at 10:16 a.m. PDT. The sun looks as if it has been slipping farther south on our horizon with each sunset until it reaches the farthest point south that it will go. At this point it appears to "stand still," which is where the word solstice comes from. Very slowly, Earth's northern axis will begin to tilt away from the sun, making it look as if the sun is moving back north on the horizon, until it reaches due west at sunset on the fall equinox.

The sun has been heading toward solar maximum, a period of greater solar activity and sunspots, which should occur within the next couple years. The newest cycle, named Cycle 24, began in 2008. The sun's complete solar cycle from one polarity back to the same polarity lasts 22 years, in which there are two smaller cycles of 11 years each where the sunspots increase to a maximum and then dip back to a minimum.

Cycle 23 and the current solar cycle have been unusual in that sunspots have been weakening so much that predictions show that there may not even be a Cycle 25. Sunspots have been observed and recorded since 1611. While the solar cycle is rather reliable, there has been a previous other instance of a "grand minimum," when solar activity went into an unexplained low. This was called the Maunder Minimum, which lasted from 1645 to 1715. Interestingly, the Maunder Minimum coincided with the Little Ice Age, when glaciers began to advance, many crops failed, and lakes and rivers were frozen over until June and July.

Are we entering another grand minimum? Would this grand minimum result in a cooler climate on Earth? Or would it somehow help to balance the climate change induced by spiking carbon dioxide levels? It is simply too soon to know.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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