…continuedA Solar Observing Refresher Course
When it comes to eyepieces for projecting the Sun's image, the much-maligned Huygenian design is a good choice because it does not contain cemented elements that can be damaged by the Sun's intense heat. Most solar projection is done onto white paper or card stock. But no matter how white the screen, it must be adequately shaded from direct sunlight and other extraneous light in order for the viewer to see the finest details in the solar image. This powerful technique enables a 4-inch telescope to produce a usable image of the Sun 30 inches across. The size and brightness of the Sun's image depend mainly on the distance between the eyepiece and the viewing surface the farther away it is, the larger and dimmer the image.
The Spotted Sun
Sunspots are cooler regions of the solar surface caused by intense localized magnetic fields that bring the upward convection of internal material to a virtual standstill. Although they appear almost black, this is merely a contrast effect. If it were possible to place a modest-size sunspot into the night sky, it would shine 10 times brighter than the full Moon!
Even the casual observer will soon learn that sunspots come in a wide variety of shapes and sizes. While the simplest sunspots are isolated dark areas, larger spots are quite dramatic. Complex spots feature a dark central region called the umbra surrounded by a gray penumbra. The penumbra normally appears as a smooth fringe, but under steady seeing conditions it may exhibit radial patterns or knots of light and dark. During those fleeting moments of good seeing you may also see tiny circular sunspots 2 arcseconds in diameter or smaller. These are called pores. Sometimes they erupt into full-fledged spots but usually they simply disappear sometimes after a lifetime of only a few minutes.
Sketching sunspots with a pencil and paper can be a rewarding way to follow their evolution. In the same way that drawing the planets sharpens your observing skills, so will regularly recording the Sun's appearance. You can follow the complex ways sunspot groups change with time, and you might even come to regard some active regions as old friends as you watch them disappear beyond the Sun's western limb and reappear on the eastern limb two weeks later. Spots near the Sun's limb sometimes appear like shallow depressions on the solar surface. This is the so-called Wilson effect, named for the 18th-century Scottish astronomer Alexander Wilson, who first called attention to the phenomenon.
More Solar Sights
The solar viewing I've described above is known as white-light observing. If you find Sun-gazing to your liking, you may choose to investigate more advanced forms of observation that use special filters to isolate portions of the spectrum for spectacular views of a wide range of phenomena. Coronagraphs, hydrogen-alpha filters, and other observing gear are available but at a significantly greater cost than the simple filters needed for white-light observing.
Riding the Solar Cycle
Solar activity varies with an 11-year cycle. As the cycle progresses, activity rises and falls, and with it the amount of detail visible on the Sun. At solar minimum, the Sun often appears nearly featureless, completely free of sunspots. At maximum, however, there can be hundreds of sunspots arranged in a half dozen or more groups and plenty of faculae. Obviously, the most exciting time to observe the Sun is in the years surrounding solar maximum. The last solar maximum was in 2000, and NOAA's Space Weather Prediction Center forecasts the next maximum for May 2013. So there's no better time than now to become a daylight astronomer!