The Swedish 1-m Solar Telescope (SST) is the largest solar telescope in Europe and number one in the world when it comes to high spatial resolution. In its superb location at the Roque de los Muchachos Observatory it combines high optical quality, adaptive optics, and advanced image restoration techniques to allow the study of solar structures in unprecedented detail. It has reached the 'dream limit' of solar telescopes by reaching a resolution of 0.1 arc seconds in blue light - this corresponds to 70 km on the solar surface. The SST is owned and operated by the Institute for Solar Physics of the Royal Swedish Academy of Sciences.
An audiovisual about the telescope is available here.
The scientific instrumentation is placed on optical tables in a laboratory environment and can thus easily be changed. Each observer can build an optical setup optimized for their own specific investigation. There is one 'imaging table' where digital cameras take images in narrowly defined wavelengths (colors), each showing different kinds of phenomena at different heights in the solar atmosphere. The light beam can be diverted to another room, where it reaches a spectrograph, used for acquiring spectra which can be used for measuring physical properties, such as the velocity, of the solar gas. Solar magnetic fields can be measured with the help of the polarization of light. These are difficult measurements requiring precision instruments and a very sharp and steady solar image.
Following extensive site testing, the Royal Swedish Academy of Sciences established its solar observatory at the Roque de los Muchachos. Our first major solar telescope - the SVST - operated here during 1985-2000 and helped revolutionizing solar observations by virtue of its high spatial resolution. The SST - with twice the aperture of the SVST - saw first light in May 2002 and immediately begun unraveling details of solar structures never before seen.
The SST is a refractor with a unique optical design. Its singlet lens made of fused silica (synthetic quartz) has a full diameter of 1.07 m and a clear aperture of 0.97 m. The light is sent down to the underground level of the observatory building with the help of two 1.4-m mirrors in the turret on top of the tower. The telescope tube is evacuated to avoid image degradation by heated air - the bottom plate of the tube is water cooled to avoid heat damage from the solar radiation. The image produced by a singlet lens is very poor because different colors are focused at different distances from the lens. The SST overcomes this problem by directing the light to a Schupmann corrector that puts all colors together at a single focus. The main obstacle of solar observations is the Earth's atmosphere, whose inhomogeneity and motions cause astronomical 'seeing' and thus blurry images - even in the extraordinary La Palma skies. Much of this can be corrected with adaptive optics - the SST has a mirror that changes shape 1000 times a second. The resulting images are subject to digital image-restoration techniques developed for the purpose.
The installation of advanced polarimetric instrumentation will allow measurements of solar magnetic fields at still higher resolution and precision. This will help solving many of the remaining riddles concerning sunspots as well as small-scale magnetic-field concentrations. At the same time improvements in our understanding of the solar atmosphere - through the interplay of improved observations and refined theory - will be beneficial to also the study of stars and other astrophysical objects.
The first data from the SST immediately showed solar structure that had not been seen before. The filaments that form the sunspot penumbrae were shown to have dark cores, regions close to sunspots were found to contain narrow dark structures dubbed 'hairs' and 'canals' - discoveries that have stimulated theoretical investigations that ultimately will help us understand the true structure of the mysterious sunspots. Images close to the edge of the solar disk - where we have a different perspective of the solar surface - showed the so-called solar faculae in extreme detail that helped solar scientists understand what this phenomenon really is. The solar faculae are important for the minute variations in the solar energy output that have been measured from satellite observatories. The transit of Venus over the solar disk on 8 June 2004 was a unique event that gave a dramatic view of the planet's atmosphere as a thin luminous aureole.