The Sun Does the Wave

The mystery of why large features called supergranules move across the Sun's surface faster than the Sun rotates has been solved, according to a team of scientists using the Solar and Heliospheric Observatory (SOHO) spacecraft. Instead of actually moving faster than the Sun, their apparent rapid rotation is an illusion generated by a pattern of activity, like fans doing the wave at a sporting event.

"This is fascinating because no theory or computer simulation had predicted what we observe," said Laurent Gizon of the W.W. Hansen Experimental Physics Laboratory (HEPL), Stanford University, Calif. Gizon is the lead author of a paper on this research that will appear in the January 2 issue of Nature.

Supergranules cover the Sun's visible surface (photosphere) in a network, called supergranulation, of cells: irregular bright regions that are horizontal outflows of electrified gas (plasma). Supergranule cells get their name from their resemblance to smaller features in the photosphere called granules. Granules are believed to be convection cells of plasma that transfer heat from the solar interior to the surface. They resemble the cells seen at the surface of a simmering pot of soup, although granules are much larger (about the size of Texas at 1,000 kilometers or about 620 miles across). Supergranules are larger still -- at around 30,000 kilometers (18,600 miles) across, they could comfortably frame two Earths. The whole solar surface is covered by several thousands of supergranules.

For more on the information on supergranules, view the complete article at: http://www.gsfc.nasa.gov/topstory/2003/0102wave.html