Astronomers have taken the most detailed pictures yet of the edge of our sun. The images, presented yesterday at the meeting of the American Astronomical Society's Solar Physics Division in Laurel, Md., are twice as clear as previous images and reveal the sun's surface to be surprisingly uneven.

Researchers led by Tom Berger of Lockheed Martin's Solar and Astrophysics Lab (LMSAL) in Palo Alto, Calif., used the Swedish one-meter Solar Telescope (SST) on the island of La Palma to inspect the visible edge of the sun, known as the solar limb. "Until recently we thought of the solar photosphere as the relatively flat and featureless 'surface' of the sun, punctuated only by an occasional sunspot," Berger says. Instead the new observations show dark sunspots nestled amoung mountainous 450-kilometer-high peaks. The surface's irregular pattern is made up of so-called granules--formed by the convection of heat--with each granule covering an area the size of Texas. In addition, the team determined the detailed structure of bright spots on the sun known as faculae (meaning "little torches"), which can reach between 150 and 400 kilometers in length.

The scientists also collected magnetic data from sunspots and faculae and compared it to the new 3-D images. They found that the more intense faculae aligned exactly with the magnetic field, supporting the link between faculae brightness and increased solar radiation during periods of high solar magnetic activity. Notes John Lawrence of California State University Northridge, "With this new discovery, we can hope to incorporate the effects of magnetoconvection into solar irradiance models to better predict variations in solar output."