This review, "Coronado's Personal Solar Telescope," appeared in the January 2005 issue of Astronomy magazine.
I've been a hydrogen-alpha (Hα) junkie since my first look through such a filter 21 years ago. I still remember my first view of prominences protruding past the limb of the Sun, filaments lying like stray hairs across its face, and bright active regions scattered around the solar atmosphere. Although I was a neophyte, I realized immediately that this was a special class of observing. Through an Hα filter, I could see a higher layer of the Sun's atmosphere and a whole new class of features — it didn't look anything like what I observed through a white-light filter.
Through the years, I stole looks through dozens of Hα filters and even owned a few. I quickly learned that the slimmer the filter's bandwidth — the little slice of the solar spectrum the filter lets through — the better the view. At narrow bandwidths, around half an angstrom (Å), the Sun's disk is almost furry — an incredible forest of contrasty details jumps out, creating an image as memorable to most people as their first views of Saturn. But as the bandwidth swells, the image gets washed out. The big problem with Hα filters, however, is expense. As recently as 10 years ago, many Hα solar filters cost more than $10,000. By the time a long-focal-ratio refractor (the preferred instrument) was added, and a sturdy mount was acquired, many people had spent as much money for a solar telescope setup as they would have for a luxury automobile.
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