for National Geographic News
The appearance last Friday of a lone dark spot on the sun signals that a new 11-year cycle of heightened solar activity is on the horizon, experts said.
Solar storms can knock out power grids, shut down satellite communications, and expose spacewalking astronauts to harmful radiation.
"We can now expect to see an increasing number of sunspots from [this new] cycle," said Douglas Biesecker, a solar physicist with the U.S. government's Space Weather Prediction Center in Boulder, Colorado.
Sunspots mark where a region of intense magnetic field from deep inside the sun emerges on its surface. The spots alone do not cause so-called space weather, but they are related to solar storms. More sunspots mean more stormy space weather.
The spots occur in cycles of increasing and decreasing activity that last approximately 11 years.
The last phase of heightened activity, dubbed Solar Cycle 23, peaked in 2000. The sunspot observed high in the sun's northern hemisphere on January 3 is the first definitely associated with Cycle 24, Biesecker explained.
"Seeing the first sunspot of the next solar cycle is important because it does mean that finally we're seeing what will be the eventual end of Cycle 23," he said.
For accounting purposes, Cycle 24 officially begins when the number of spots associated with it outnumbers the sunspots associated with Cycle 23, he added. That should occur within months.
David Hathaway is a solar physicist with the NASA Marshall Space Flight Center in Huntsville, Alabama. He equated last week's sunspot to the first kernel in a batch of popcorn going off.
"It takes them going off repeatedly before the new cycle takes over," he said.
What to Expect
Highly charged material ejected from the sun during solar storms causes power outages and disrupts satellite communications that can affect everything from taking cash out of an ATM to chatting on a cell phone.
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