Optical Filters for
Solar Observation

Space Weather Prediction Center. https://www.swpc.noaa.gov

White light solar filters are the most affordable for the amateur astronomer. They are typically made from a durable glass or polymer film that attenuates the transmission of light from the sun to a fraction of a percent. Utilizing white light filtering, one sees the sun’s photosphere as a soft yellow solar disk and is able to see the solar granulation of the surface, as well as occurring sunspots. White light is good for viewing and documenting day-to-day or week-to-week changes.

If you are looking for real-time excitement, one needs to go no further than the Hydrogen-Alpha line filter at 656.28nm. According to the Observer’s Guide to the H-Alpha, written by Bob King, “Viewed in a narrow slice of the spectrum centered in the ruby red H-Alpha, the sun broils with activity. Prominences, spicules, fibrils, Ellerman bombs, flares and more seethe and boil before your eyes. Unlike white light, the H-Alpha pulls back the curtain to expose the beast for what it is, a ferocious, unpredictable ball of incandescent hydrogen gas.” The H-Alpha bandpass filter is utilized in many solar telescopes in conjunction with a red glass filter, dichroic filter, and Fabry-Perot etalon to cancel out the undesired wavelengths, giving an artificial solar eclipse any sunny day of the year. Being able to see the edge of the sun will reveal a close-up view of solar flares, mass ejections, and other solar activities not visible through white light filtering.