Jimmy Westlake: The return of the sunspots
February 16, 2010
Steamboat Springs — After a remarkable two-year hiatus, sunspots are coming back. This prolonged sunspot minimum is the longest in a century and has kept solar astronomers on the edge of their seats. If recent activity is any indicator, then the sunspot minimum may be over at last.
Sunspots were discovered 400 years ago by famed Italian astronomer Galileo Galilei. He watched the sunspots drift across the face of the sun and concluded that the sun rotates on its axis about once every 28 days. Shortly after they were discovered, however, the sunspots disappeared. Other astronomers tried to duplicate Galileo's observations in the following decades, but the sun refused to cooperate.
Between the 1640s and the 1720s, the sun stopped producing sunspots. Then, just as suddenly and mysteriously as they had disappeared, the sunspots returned. This prolonged period of sunspot inactivity is called the Maunder Minimum, after the English astronomer Edward Maunder who first drew attention to it. This same interval of time coincided with an extremely cold period in Europe known as the Little Ice Age.
It wasn't until the 1840s that German astronomer Heinrich Schwabe discovered that daily sunspot numbers increase and decrease in an 11-year cycle of solar activity. That is, every 11 years, the sun breaks out all over with large and active sunspot regions before settling down into a relatively quiet period of inactivity. Solar scientists think the 11-year sunspot cycle is tied to the sun's differential rotation. The sun's equator rotates in about 25 days while the polar regions require 30 days or more to rotate. This shearing effect causes the sun's powerful magnetic field to get all twisted up and wrapped around the sun until, every 11 years, the magnetic field lines kink up and poke through the solar surface creating sunspots.
The last solar maximum occurred around the years 2001 and 2002, followed by a solar minimum that began in 2007. Astronomers expected the new solar cycle to begin in 2008 or 2009, but day after day passed with no sunspots. The year 2009 registered 260 days, or 71 percent of the year, with zero sunspots. Then, with the ringing in of the year 2010, the sun began to awaken from its deep slumber as one sunspot group after another popped up and solar astronomers let out a collective sigh of relief. Since Jan. 1, there have been only two days, or 4 percent of the year, with zero sunspots. If this current trend continues, we could see the next solar maximum around 2013 and 2014.
For more information, photographs and updates on current solar activity, visit NASA's Web page devoted to all things solar, http://www.spaceweather.com.
Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Check out Westlake's Web site at http://www.jwestlake.com.