An image of a very dynamic sun compared to a sun deep in solar minimum helps to illustrate the extremes of a solar cycle. Image Credit: SOHO, NASA/ESA
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The sun is finally starting to wake up after oversleeping a few years.
At first, scientists thought solar activity would pick up in fall 2006. Then the forecast changed to late 2007 or early 2008. Only since this past December, however, has sunspot activity shown a marked increase.
Sunspots are localized areas of strong magnetic field that are visible as dark spots on the sun's surface. The number of sunspots is representative of overall solar activity - the more sunspots there are, the more active the sun is and the greater the impact on Earth.
Observations going back more than 300 years show it typically takes approximately 11 years for the annual number of sunspots to vary from a minimum to a maximum and back to a minimum. Each of these approximately 11-year periods is known as a solar cycle.
Solar Cycle 23 started in 1996 and peaked from 2000 to 2002. Solar Cycle 24 is considered to have started in January 2008. But it has been very slow to get going until the recent increase, with solar activity nearing or setting record lows in 2008 and 2009.
As for the strength of Solar Cycle 24, scientists predicted in 2006 it would be stronger than the previous cycle and peak in 2012. However, subsequent forecasts have estimated the current cycle will be weaker than the last and reach a maximum in 2013.
The Solar Dynamics Observatory studies many wavelengths of light simultaneously. Image Credit: NASA
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One lesson from the uncertain and fluctuating forecasts of Solar Cycle 24 is that scientists have a lot more to learn about how the sun works. That's where NASA's Solar Dynamics Observatory, or SDO, enters the picture. SDO was launched into space in February 2010 and aims to give scientists the most detailed view ever of the sun and its inner workings.
SDO is scheduled to take images of the sun every few seconds during its planned five-year mission. The spacecraft's three primary instruments will make measurements of the sun's interior and magnetic field; the hot plasma of the solar corona, the uppermost level of the sun's atmosphere; and the amount of energy the sun emits.
A better understanding of these and other components of solar activity is expected to improve predictions of solar cycles and of solar storms - explosions of energy from the sun that can zap power grids, interfere with communications on Earth and, potentially, harm astronauts in space. Improved knowledge and forecasts of solar activity can help protect against these and other hazardous impacts.
Solar Dynamics Observatory