Sunspots with fascinating details
Sunspots represent darker, cooler areas on the sun’s surface. They occur primarily in times of increased solar activity and can grow to diameters as large as planets. The center of a sunspot, the umbra, is surrounded by a brighter outer part called the penumbra. This penumbra consists of long filaments that are wrapped around the center like hair. With the help of the Swedish Solar Telescope, astronomers discovered for the first time that many of these filaments have a dark inner core. According to Professor Göran Scharmer, Director of the Swedish Institute for Solar Physics, these cores are between 150 and 180 kilometers wide and possibly originate from magnetic flux tubes that transport hot plasma. However, scientists are still unclear about their exact explanation.
Mountains several hundred kilometers high
Special features of solar telescope constructions
At present the Swedish Solar Telescope is the largest in Europe and the second largest in the world after the McMath-Pierce Telescope in Arizona. However, three new projects are planned or are already under construction. On the island of Tenerife the 1.5-meter solar telescope GREGOR of the Kiepenheuer Institute for Solar Physics (KIS) in Freiburg, Germany, will start operations in 2004. A solar telescope with a 1.7-meter mirror made from “ZERODUR®” is set to be built at the Big Bear Solar Observatory (BBSO) in California by the year 2006. SCHOTT has already supplied the mirror blank for this project. And a 4-meter telescope (ATST = Advanced Technology Solar Telescope), which will probably be the basis for the next generation of solar telescopes, is currently under consideration. Due to their size, none of these future observatories can be constructed as a vacuum telescope. Their design will instead require open mirror systems with a special cooling method.