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GlassDarkly

Sky & Telescope magazine in September 1989 ran a article titled "Viewing Sunspots with Just a Filter" (on pps. 289 & 291). A copy surfaced here yesterday, crumpled and yellowed and dusty, from behind a book on our overcrowded mantel when I moved one volume to make way for another.

The author, identified only as "A. M.", describes how to observe the solar disk safely with minimal expense or equipment. The trick is to use a slab of #14 welder's glass, a standardized quality-controlled filter that cuts light by a factor of exp(-14), so only one photon in every million gets through. That lowers the Sun's brightness from an apparent magnitude of -27 down to -12, about the same as a full Moon. (see LogScales (23 Feb 2000))

I remember back in '89 when, encouraged by this very article, I ventured into a local welding supply store charmingly named Roberts' Oxygen. I bought a dozen #14 filters. They cost less than a dollar each. For years thereafter I was the neighborhood cynosure as I stood by the street and looked at partial solar eclipses and major sunspot groups. Most of those slabs of welder's glass are long gone, given away to friends, passers-by, and curious children. But I still have a couple stashed away. (Important Safety Tip: don't try to observe the Sun with anything less than a #14 shade, and never use the filter with any light-gathering device such as binoculars or a telescope.)

The S&T article concludes with an inspirational suggestion:

A long series of 1-power drawings might not only allow you to "discover" the solar cycle but also the Sun's differential rotation (the Sun rotates faster at its equator than near its poles) and perhaps much else. The possibilities serve as a reminder of how much a diligent observer can accomplish with the "naked" eye.

I was never disciplined enough to keep a notebook of my own solar sketches. Perhaps some day ....

(see also NoiseAndPredictability (14 Sep 1999), Nobel Neutrinos (13 Oct 2002), ...)


TopicScience - TopicPersonalHistory - Datetag20030101


(correlates: 1 Comment on Contemporary Introduction to Free Will, CountrySightsAndSounds, CatchingOn, ...)