[SQM] measuring method question

Doug Kniffen dkniffen at centurytel.net
Thu Feb 28 18:43:36 UTC 2008

Finally got a chance to try out the sky quality meter last night.  The sky appeared better than average visually. Background at zenith was Mag. 20.68 per square arc second.

Looking forward to measuring night by night changes here, and the possibility of rating multiple sites on a single night. Out of the box, a zenith measurement is really only useful for comparing instrumental limitations of different sites. So one prime goal is to find the best way to compare sites for visual use because even the luminance off the grass may effect night vision. After a satisfactory way of measuring total site luminance is found I'd like to identify the range of values over which rod vision becomes precluded from naked eye perception.

Part of the motivation for this is the realization that satellite images and light pollution maps alone are not ideal for identifying good visual observing sites.  This point is illustrated by a comparison between this location and the club observing site.  Naked eye visual comparison indicates both locations are similar. From LP maps the club site appears considerably more light polluted, but from on ground inspection the club site has no lights within a mile. From LP maps this location should be less polluted, but there are dozens of lights within a mile. Yet both sites have similar visual observing potential.

First thought for measuring total environmental luminance at any given site was a ping pong ball suspended above the sensor window. Second thought was one of those "all sky" hub cap mirrors. Third thought was an entry door peep hole lens assembly.  Anybody have better ideas?

Thanks in advance,

Doug Kniffen

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