Solar telescopes need optics large enough to achieve the best possible diffraction limit but they do not need the associated light-collecting power of other astronomical telescopes. Because solar telescopes are operated during the day and image a very bright object, and because the seeing limit imposed by atmospheric turbulence is much worse than that experienced by night-time telescopes, the objectives of such telescopes are about 1m or under in diameter. The heat generated by the tightly-focused sunlight also poses a design problem. Professional solar observatories may have main optical elements with very long focal lengths and light paths operating in a vacuum to eliminate air motion due to convection inside the telescope. Since this makes the telescope relatively massive (some are the most massive optical telescopes in the world), and the object that they image (the Sun) travels on a narrow fixed path across the sky, solar telescopes are usually fixed in position (sometimes buried underground) with the only moving part being a heliostat to track the sun. These telescopes use filtration and projection techniques for direct observation, in additional to filtered cameras of various types. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine the sun in different wavelengths.
In the field of Amateur astronomy there are many methods used to observe the sun. Amateurs use everything from simple systems to project the sun on a piece of white paper up to hydrogen-alpha filter systems and even home built spectrohelioscopes. In contrast to professional telescopes, amateur solar telescopes are usually much smaller.
Encyclopedia
top
