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Mr. Bill
Post Laureate
Reged: 02/09/05
Posts: 3147
Loc: Just passing through.....
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Transparency variability.....
06/28/09 01:24 PM
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Under very dark skies the transparency of the atmosphere can change noticeably over a period of minutes.
This was easily noticeable at the GSSP on Monday night when the Milky Way would ebb and flow in size and structure after midnight. It was commented on by several very experienced observers that I was hanging out with.
Differences in contrast correlated highly with my readings using a Sky Quality Meter (SQM.) Readings of the same part of the sky both away and at the MW showed variability of 0.3 magnitudes over a couple of hours.
This is largely caused by excitation of oxygen in the upper atmosphere and can vary over scales of minutes, much as an aurora display but much more subtle.
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10x50 Fujinon binos + 16x70 Fujinon binos + UA UniMount
Oberwerk BT100 45 degree +24mm Pans + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
130mm TMB 130SS f/7 APO refractor
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/8 homemade achromat
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery "Galactic Cannon"
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