A huge sunspot over a dozen times larger than the surface area of the Earth and growing, has now rotated with the Sun to face our planet. The sunspot, which is the largest of the current solar cycle, is also the largest to appear in a decade.

This picture of the largest sunspot group in a decade shows the Sun in white light as seen by the National Science Foundation's Global Oscillation Network Group (GONG) instrument in Big Bear, CA., on March 30. Photo: NSO/AURA/NSF

The area of the Sun, designated AR 9393, has been a prolific generator of stormy solar activity, hurling clouds of electrified gas towards Earth, producing four explosions, called flares, and spawning storms of high-speed particles in space.

The largest of the four flares occurred at 4:57 a.m. EST on Thursday, March 29, and was rated as an X-class flare, the most potent designation. The other three flares were rated M- class, second only to the X-class. An eruption near AR 9393 hurled a cloud of electrified, magnetic gas towards Earth on Wednesday. This eruption, called a Coronal Mass Ejection may cause auroral displays and magnetic storm activity when it impacts the Earth's magnetic field sometime Friday. Another Earthbound CME associated with the X-class flare was seen at 5:26 a.m. EST March 29 and is expected to arrive on Saturday.

"Sunspots with complex magnetic field structures like those in AR 9393 can generate big flares, and sure enough, we just had a powerful X-class flare from this area," said Dr. Joseph Gurman, at NASA's Goddard Space Flight Center, Greenbelt, MD, project scientist for the Solar and Heliospheric Observatory (SOHO) spacecraft. SOHO is one of a fleet of sun-observing spacecraft now tracking this region and its activity.

This view is a collage of images taken on March 27 at the National Science Foundation's Richard B. Dunn Telescope at the National Solar Observatory in Sunspot, New Mexico. This whole sunspot covers more than 140,000 kilometers (86,8000 miles), 22 times the diameter of Earth, over the Sun's northern hemisphere. Photo: NSO/AURA/NSF (K. S. Balasubramaniam, M. Sigwarth, R. Radick, S. Hegwer, J. Elrod and S. Fletcher.)

Sunspots are darker areas on the visible surface of the Sun caused by a concentration of distorted magnetic fields. The strong magnetic field slows the flow of heat from the Sun's interior and keeps sunspots slightly cooler than their surroundings, causing them to appear dark. The number of sunspots increases and decreases as the Sun's 11-year cycle of stormy activity rises and falls. Violent solar activity is believed to be caused by the release of magnetic energy, and powerful solar eruptions and flares often occur near the enhanced magnetic field of sunspots.

Solar flares, among the solar system's mightiest eruptions, are tremendous explosions in the Sun's atmosphere, capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds flares can accelerate solar particles to very high velocities and heat solar material to tens of millions of degrees.

Coronal mass ejections are clouds of electrified magnetic gas weighing billions of tons, hurled into space at speeds of 12 to 1,250 miles per second. Depending on the orientation of the magnetic fields carried by the ejection cloud, solar explosions cause magnetic storms by interacting with Earth's magnetic field, distorting its shape and accelerating electrically charged particles trapped within.

This picture of the largest sunspot group in a decade shows the Sun as seen by a film camera at the National Science Foundation's McMath-Pierce Telescope at Kitt Peak, AZ, on Friday morning, March 30. Photo: NSO/AURA/NSF

Severe solar weather is often heralded by dramatic auroral displays, but magnetic storms are occasionally harmful, potentially affecting satellites, radio communications and power systems.

Coronal Mass Ejections and flares can produce storms of high- velocity particles. The ejections are believed to produce longer particle storms than flares, storms that sometimes last for days, as they plow through the slower solar wind at supersonic speeds, creating a shock wave that accelerates electrically charged particles.

The SOHO project is an international cooperative program between NASA and the European Space Agency in the framework of the international Solar Terrestrial Science Program.