According to Todd Hoeksema, director of the Wilcox Solar Observatory at Stanford University, the sun goes through a natural cycle that averages 22 years. In each half-cycle, areas of intense solar magnetic activity known as sunspots gradually move from the sun's equatorial region toward the poles, eventually disrupting the magnetic fields at the star's North and South. Eventually, the sun's magnetic field shuts down entirely, then reboots with the positive and negative poles at opposite sides.
"It's kind of like a tide coming in or going out," Hoeksema said. "Each little wave brings a little more water in, and eventually you get to the full reversal."
This cycle then repeats, ending when the poles are back in their initial locations. The recent reversal marks the midpoint of Solar Cycle 24, which began in 2002.
NASA video shows reversalEarlier in December, solar physicists announced that "the sun's north pole has already changed sign, while the South Pole [sic] is racing to catch up."
Solar Cycle 24 has been full of surprises. It was initially predicted to reach its midpoint in 2012, but scientists revised this estimate to 2013 when 2009 was marked by "extremely low activity" that, if it continued, could have led to another Little Ice Age.
To mark the long-anticipated solar reversal, NASA has released a video simulation of the second half of Solar Cycle 23.
"A reversal of the sun's magnetic field is, literally, a big event," said Tony Phillips of NASA.
The video begins in 1997, showing the sun with its positive polarity (marked by green lines) at the top and its negative polarity (purple lines) at the bottom. The video shows the lines gradually moving toward opposite ends of the sun, having completely switched places by 2002. This marked the end of Solar Cycle 23 and the beginning of the current cycle.
Cosmic effectsThe solar reversal will have significant effects that reach past our own solar system, although few of them will be felt on Earth.
"At the height of each magnetic flip, the sun goes through periods of more solar activity, during which there are more sunspots, and more eruptive events such as solar flares and coronal mass ejections," said NASA's Karen C. Fox.
For us on Earth, these effects will mostly be limited to an increase in the breadth, frequency and visibility of the aurora borealis and aurora australis - the Northern and Southern Lights. The magnetic reversal might also lead to freak geomagnetic storms, temporarily disrupting satellite or radio signals.
"It's not a catastrophic event," Hoeksema said, "it's a large scale event that has some real implications, but it's not something we need to worry about."
In outer space, however, the effects will be felt more strongly.
"The domain of the sun's magnetic influence (also known as the 'heliosphere') extends billions of kilometers beyond Pluto," Phillips said. "Changes to the field's polarity ripple all the way out to the Voyager probes, on the doorstep of interstellar space."
"Cosmic rays are also affected," he said. "These are high-energy particles accelerated to nearly light speed by supernova explosions and other violent events in the galaxy."
These effects may impact space exploration. Intensified cosmic rays, for example, might damage space probes or even pose physical dangers to astronauts. They might also have effects on Earth's climate, although the exact nature of these effects remains unclear.