4. How Does the Sun Shine?

2005

24 May 2005. Solar Fireworks Signal New Space Weather Mystery. NASA RELEASE 05-132. The most intense burst of solar radiation in five decades accompanied a large solar flare on January 20. It shook space weather theory and highlighted the need for new forecasting techniques, according to several presentations at the American Geophysical Union (AGU) meeting this week in New Orleans. The solar flare, which occurred at 2 a.m. EST, tripped radiation monitors all over the planet and scrambled detectors on spacecraft. The shower of energetic protons came minutes after the first sign of the flare. This flare was an extreme example of the type of radiation storm that arrives too quickly to warn interplanetary astronauts. "This flare produced the largest solar radiation signal on the ground in nearly 50 years," said Dr. Richard Mewaldt of the California Institute of Technology, Pasadena, Calif. ... "But we were really surprised when we saw how fast the particles reached their peak intensity and arrived at Earth." Normally it takes two or more hours for a dangerous proton shower to reach maximum intensity at Earth after a solar flare. The particles from the January 20 flare peaked about 15 minutes after the first sign. ...The Transitional Region and Coronal Explorer (TRACE) ... has identified a possible source of the magnetic stress that causes solar flares. The sunspots that give off the very largest (X-class) flares appear to rotate in the days around the flare. "This rotation stretches and twists the magnetic field lines over the sunspots", Nightingale said. "We have seen it before virtually every X-flare that TRACE has observed since it was launched and more than half of all flares in that time." However, rotating sunspots are not the whole story. The unique flare came at the end of a string of five other very large flares from the same sunspot group, and no one knows why this one produced more sudden high energy particles than the first four. "It means we really don't understand how the sun works," Lin said. "We need to continue to operate and exploit our fleet of solar-observing spacecraft to identify how it works."

2004

18 October 2004. Science@NASA. Solar physicist David Hathaway has been checking the sun every day since 1998, and every day for six years there have been sunspots. Sunspots are planet-sized "islands" on the surface of the sun. They are dark, cool, powerfully magnetized, and fleeting: a typical sunspot lasts only a few days or weeks before it breaks up. As soon as one disappears, however, another emerges to take its place. Even during the lowest ebb of solar activity, you can usually find one or two spots on the sun. But when Hathaway looked on Jan. 28, 2004, there were none. The sun was utterly blank. It happened again last week, twice, on Oct. 11th and 12th. There were no sunspots. "This is a sign," says Hathaway, "that the solar minimum is coming, and it's coming sooner than we expected.