Last updated: 15 September 2003
Subject: Star testing your ETX scope: in daylight! Sent: Wednesday, September 3, 2003 11:44:31 From: email@example.com (Bob Morris) My neighbour's ashphalt shingled shed is about 50 ft from a picnic table in my back yard. Its roof is maybe 8-10 feet off the ground. I'd thought the fine grained shingle granules would be a neat object to test focus on. However, at a specific time of a sunny day, with the scope slightly out of focus, I noticed that certain isolated random granules were picking up the sun and giving intense diffraction ring patterns, standing out from the background. In focus, you can see a single ceramic granule reflecting the sun with adjacent granules not. Typically with a 26 mm eyepiece, about 1/2 dozen "stars" of varying intensity shine out. There is usually one brighter than the others. This is on a roof about 7 years old. On a new one, there would be more reflecting granules. I had observed before that new black-shingled roofs are very "sparkly." Real stars have atmospheric effects. These very bright artificial stars are a near-point source of a very bright light with only 50 feet of atmosphere between the scope and them. Bottom line: I have never seen such intense, steady, contrasty diffraction ring patterns on my ETX-90 as from ashphalt shingles at the correct sun angle. In recent weeks, observing at about 4 pm in the afternoon seems to work nicely. Try it, you'll like it! Bob MorrisMike here: Interesting tip. Sort of like the "Christmas Tree Ornament" test, which also uses a pinpoint reflection of the Sun as a light source.
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