Solar filters for observing the Sun
Most experienced Sun-watchers prefer specially designed solar filters that reduce the Sun’s energy to harmless levels. Filters come in two main categories: First are white-light filters. These block 99.999 percent of sunlight to allow us to see the Sun’s visible surface, or photosphere, revealing wonderful views of constantly evolving sunspots. Second are Hydrogen-alpha (Hα) filters. These block all wavelengths of sunlight except for one — the wavelength emitted by hot hydrogen atoms. Hα filters reveal details on the Sun that are invisible using white-light filters, including flamelike prominences and intricate bright threads called solar plages, which are usually found near sunspots.
Known as “aperture filters,” white-light filters fit over the front of a telescope in order to reduce the Sun’s energy to a safe level before it enters the optical system, including your eyes. They are commonly made from glass or a polymer material, such as Mylar, and fit securely on a telescope or binoculars (although you will need two filters for the latter, one per barrel).
White-light filters should only be purchased from a reputable source. Some of the most popular include Astrozap (astrozap.com), Baader Planetarium (astrosolar.com/en), Celestron (celestron.com), Explore Scientific (explorescientificusa.com), Kendrick Astro Instruments (kendrickastro.com), Meade Instruments (www.meade.com), Orion Telescopes (www.telescope.com), and Thousand Oaks Optical (thousandoaksoptical.com).