Images reveal greater sunspot structure.

Images reveal greater sunspot structure

Photographs taken with the McMath optical telescope on Kitt Peak near Tucson, Ariz., reveal new details about sunspots, the solar regions where magnetic fields concentrate. The image on the left depicts a conventional view: Filaments of gas -- believed to mark the path of magnetic field lines parallel to the solar surface -- extend radially from a sunspot's outer edge, or penumbra. They do not appear to extend back into the sunspot's darker central region, or umbra. But when astronomer William Livingston of the National Solar Observatory in Tucson took a longer-exposure photo, he detected filamentary "bridges" spanning the penumbra and umbra -- an indication that magnetic field lines cross into the central region. The image on the right, a composite of the long and short exposures, delineates the bridging filaments.

Livingston says his images challenge the accepted view that the umbra has a relatively uniform, granular structure. Instead, it contains filaments separated by dark voids where the magnetic field points perpendicular to the solar surface, he asserts. The new umbral detail also indicates that temperatures may vary significantly over the region, Livingston notes. He credits his findings to the Kitt Peak telescope's high resolution and to excellent viewing conditions. But he adds that other observers may have ignored similar evidence because it did not support the granular theory.