We can see the sun from both sides now

The hidden face of the sun is fully visible for the first time, thanks to a technique developed at Stanford (Calif.) University. Only half of the sun--the near side--directly is observable. The far side always faces away from Earth and therefore is out of view.

New technology, however, allows anyone with a computer to download images of the entire solar surface--an important advance with practical applications, say researchers, because potentially damaging solar storms that form on the far side now can be detected several days, or even weeks, before they wreak havoc on Earth.

"Sunspots, solar flares, and other active regions on the surface of the sun emit radiation that can interfere with orbiting satellites, telecommunications, and power transmission," observes Philip Scherrer, research professor in the Department of Physics. "This new method allows more reliable warning of magnetic storms brewing on the far side that could rotate with the sun and threaten the Earth."

It takes about 27 days for the sun to rotate on its axis, so an active region that forms on the far side can remain hidden for up to 13 days and surprise Earth-bound observers when it finally rotates into view. That is what happened in October 2003 when active regions from the back side suddenly appeared on the eastern edge of the sun, spewing X-rays, ultraviolet radiation, and high-energy particles into space.

Scherrer and his colleagues study the sun using data from SOHO (Solar and Heliospheric Observatory), a research satellite launched in 1995 by NASA and the European Space Agency. On board SOHO is the highly sophisticated Michelson Doppler Imager (MDI), an electronic instrument that creates images of the sun's interior by measuring the velocity of sound waves produced by hot, bubbling gases that well up to the surface--a technique called acoustic helioseismology.

"Helioseismology works on the same principle as medical ultrasound, which can create an image of a fetus inside a pregnant woman," Scherrer explains. "In this case, we're looking through a star with sound waves."

Positioned high above the Earth, the SOHO satellite always faces the visible side of the sun. The problem finally was overcome last summer when a new computer algorithm was developed by the Stanford SOHO-MDI team in collaboration with Kenneth Oslund, an undergraduate at the California Institute of Technology, Pasadena. Their work resulted in the MDI Farside Graphics Viewer, which displays the first full images of the far side of the sun.

"This new method is a vast improvement," Scherrer emphasizes. "It should be especially important during the next solar maximum, which should begin in 2011, when solar activity will be at its peak."

He points out that, during the last "solar max," which lasted from 2000-03, solar storms temporarily knocked out power in the northern parts of Sweden and Canada and destroyed a satellite that was used to verify credit card payments at numerous gas stations in the U.S. Air transportation also can be disrupted when solar radiation interferes with the operation of Global Positioning System satellites, or when aircraft that take shortcuts over the North Pole have to employ longer routes to prevent passengers and crew from being exposed to intense X-ray radiation.

"Our goal is to give pilots and air traffic controllers a day or two notice of a possible solar event," Scherrer concludes, adding that missions to Mars and other planets also can be affected when solar storms interfere with satellite communications to Earth. In fact, researchers at the National Center for Atmospheric Research in Colorado recently released new computer models predicting that the next solar cycle will be 30-50% stronger than last time.

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