[AZ-Observing] Re: Question about clear sky statistics in Arizona & Tucson
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 13 Aug 2001 14:28:20 -0700 (MST)
I'd be surprised to learn that the clear-sky statistics for Tucson
are dramatically different than for Flagstaff. In round numbers: about 100
photometric (cloudfree dusk-to-dawn) nights annually, and about another 100
nights either partly clear or with thin cirrus only. In his last several
years at Lowell, Ray Bertram kept records of "workable" nights when he was
using the 1.8-m telescope (as the OSU observer). Since he was doing
spectroscopy, and wasn't picky about exposure times, he found that there
weren't very many nights (10-15% only) where he couldn't get any data at all.
But when you get to where you're taking a 2-hour exposure on something that
shouldn't take more than 20 minutes you start to wonder about the science per
dollar ratio. But you can get desparate for transient events.... I'm pretty
sure I wouldn't call such nights "clear", however.
If you scan through the main decadal indexes for PASP under the topic
"observatory sites" you'll find some papers with seeing and cloudiness stats
for KPNO, Sac Peak, and Flagstaff. All use less restrictive definitions
of "clear" than mine, but not as bad as the chamber of commerce would use.
\Brian
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