This article originally appeared in the May, 2010 issue of Astronomy.
Many observers consider the Sun the ultimate celestial villain because it robs them of valuable telescope time. But look on the bright side (pun intended). The Sun is easy to find and offers plenty of detail. Plus, you’ll get great views through any size telescope, and capturing solar images takes little time.
Be safe, not sorry
The first item of business for any solar observer is eye safety. Make sure you use an approved solar filter from a reputable manufacturer. This isn’t something that you can make yourself out of shiny candy wrappers. High-quality solar filters remove infrared and ultraviolet radiation and allow only a small fraction of the Sun’s visible light through. Also, never use a solar filter that attaches to an eyepiece. A solar filter must cover the entire front end of your telescope. That’s where the light enters. If you need convincing, see Glenn Chaple’s “Observing Basics” column in Astronomy’s January 2010 issue.
Pick a viewing method
Actually, there is one way you can view the Sun without a filter: Use your telescope for solar projection. Observers who favor this method trace the Sun’s disk and any visible sunspots. This technique provides better positional accuracy over sketching freehand. Manufacturers classify solar filters by the wavelengths of light they transmit. The most popular are visible-light filters. As the name implies, these filters transmit visible wavelengths (at a much reduced level). Visible-light solar filters allow you to see sunspots, granulation (surface mottling), occasional faculae (small bright areas), and limb darkening. The next most-popular filter allows only light with a wavelength of 656.28 nanometers to pass through. That wavelength marks an emission of red light that occurs when an electron in a hydrogen atom drops from the third to the second energy level. Physicists labeled this emission Hydrogen-alpha (Hα), so you’ll need an Hα filter to see it. Hα observing allows amateur astronomers to view normally hidden solar features like the chromosphere (the layer beneath the visible surface) and prominences. Through these filters, solar flares appear as white regions on the Sun’s disk, and often such features change in mere minutes. The only reason Hα observing is less popular than visible-light observing is cost. Hα filters typically cost 10 to 50 times as much as visual ones.