Solar Cycle 24 Begins
Jan. 10, 2008: Hang on to your cell phone, a new solar cycle has just begun.
"On January 4, 2008, a reversed-polarity sunspot appeared—and this signals the start of Solar Cycle 24," says David Hathaway of the Marshall Space Flight Center.
Above: Images of the first sunspot of Solar Cycle 24 taken by the NASA/ESA Solar and Heliospheric Observatory (SOHO).  [Movie]
Solar activity waxes and wanes in 11-year cycles. Lately, we've been experiencing the low ebb, "very few flares, sunspots, or activity of any kind," says Hathaway. "Solar minimum is upon us."
The previous solar cycle, Solar Cycle 23, peaked in 2000-2002 with many furious solar storms. That cycle decayed as usual to the present quiet leaving solar physicists little to do other than wonder, when would the next cycle begin?
"New solar cycles always begin with a high-latitude, reversed polarity sunspot," explains Hathaway. "Reversed polarity" means a sunspot with opposite magnetic polarity compared to sunspots from the previous solar cycle. "High-latitude" refers to the sun's grid of latitude and longitude. Old cycle spots congregate near the sun's equator. New cycle spots appear higher, around 25 or 30 degrees latitude.
The sunspot that appeared on January 4th fits both these criteria. It was high latitude (30 degrees N) and magnetically reversed. NOAA named the spot AR10981, or "sunspot 981" for short.
Sunspot 981 was small--only about as wide as Earth, which counts as small on the grand scale of the sun--and it has already faded away. But its three day appearance on Jan. 4-6 was enough to convince most solar physicists that Solar Cycle 24 is underway.predicted that Solar Cycle 24 would begin around March 2008 and it looks like we weren't far off," he says.
Right: The first auroras of the new solar cycle, photographed Jan. 4, 2008, by Calvin Hall of Palmer, Alaska. [more]
The onset of a new solar cycle is significant because of our increasingly space-based technological society.
"Solar storms can disable satellites that we depend on for weather forecasts and GPS navigation," says Hathaway. Radio bursts from solar flares can directly interfere with cell phone reception while coronal mass ejections (CMEs) hitting Earth can cause electrical power outages. "The most famous example is the Quebec outage of 1989, which left some Canadians without power for as much as six days."
Air travel can be affected, too.
Every year, intercontinental flights carry thousands of passengers over Earth’s poles. It's the shortest distance between, say, New York and Tokyo or Beijing and Chicago. In 1999, United Airlines made just twelve trips over the Arctic. By 2005, the number of flights had ballooned to 1,402. Other airlines report similar growth.
"Solar storms have a big effect on polar regions of our planet," says Steve Hill of the Space Weather Prediction Center. "When airplanes fly over the poles during solar storms, they can experience radio blackouts, navigation errors and computer reboots all caused by space radiation." Avoiding the poles during solar storms solves the problem, but it costs extra time, money and fuel to "take the long way around."
Above: An increasing number of international business flights cross Earth's Arctic to save time, fuel and money. 
Now for the good news: More solar storms also means more auroras—"the greatest show on Earth." During the last solar maximum, Northern Lights were spotted as far south as Arizona, Florida and California. Not so long ago, only visitors to the Arctic regularly enjoyed auroras, but with increasing attention to space weather and constantly improving forecasts, millions of people at all latitudes will know when to go out and look.
Much of this is still years away. "Intense solar activity won't begin immediately," notes Hathaway. "Solar cycles usually take a few years to build from solar minimum (where we are now) to Solar Max, expected in 2011 or 2012."
It's a slow journey, but we're on our way.
Strange but True: While Solar Cycle 24 has begun, Solar Cycle 23 has not ended. Both cycles will coexist for a period of time, perhaps a year or more, as one dies down and the other comes to life. In the months ahead we may see old-cycle sunspots and new-cycle sunspots on the sun at the same time.
NASA is gearing up to study the active sun during Cycle 24 with the launch of a new spacecraft, the Solar Dynamics Observatory. "SDO is a very special observatory," says project scientist Dean Pesnell at NASA's Goddard Space Flight Center, Greenbelt, Md. "Using a technique called helioseismic imaging, the spacecraft will be able to look inside the sun where solar activity begins. SDO will join SOHO, STEREO, Hinode and other missions already in orbit to improve our understanding of solar storms and lay the groundwork for better space weather forecasts."
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