FreeLists / az-observing / [AZ-Observing] McDonald Obs SQM measurements

[Brian Skiff <bas@xxxxxxxxxx>]

     I am in the middle of a nine-night observing run at McDonald Observatory
helping with photometry and spectroscopy of T Tauri stars.  I brought
my SQM sky-brightness meter, and have made several measurements on
the photometric nights prior to Moonrise.  Although there are four
nights remaining, I'm pretty sure we will have no more cloud-free sky.
So here are numbers, obtained in the usual manner, though since the
summit area near the telescopes is a very nice aerie, it is easy to
find unobstructed places to make the measurements.

UT Date  hhmm  LST   site   mu    pv    dp   remarks
                                 (mm)  (C)
20070206 0215        McD   21.50       -10   ~1500 particles/foot^3
20070206 0315        McD   21.58       -10   horiz vis 200+ km
20070207 0200        McD   21.58       -10   ~2000 particles/foot^3
20070207 0300        McD   21.55       -10   horiz vis 200+ km
20070207 0400        McD   21.53       -10
20070210 0200        McD   21.51        -5   ~2200 particles/foot^3
20070210 0300        McD   21.54        -5   horiz vis ~200km
20070210 0400        McD   21.58        -5
20070210 0500        McD   21.52        -5
20070210 0600        McD   21.61        -5

I haven't figured the sidereal times yet, but they run from about 4h
at dusk to 8h for the last entry.  
     On the first two days, the air was quite transparent, with 
very little scattered light----probably fairly standard for mid-winter
at this site.  Today the aerosols were up somewhat.  Because they
are subject to very dusty episodes, the observatory maintains a
nephelometer that reads out in particles per cubic foot (not the units
I would choose...), so I show typical values for each night as a
proxy for horizontal transparency and aerosols.
     The sky brightness values themselves are essentially identical
to what I get at Anderson Mesa, or perhaps ~0.1 mag fainter, at similar
sidereal time (winter Milky Way and zodiacal light within the 
acceptance angle of the SQM detector).  I would estimate the values
would fall to ~21.8 late at night with the galactic pole overhead.

\Brian
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