[sac-forum] Re: Messier Marathon results questions

Original Message:
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From: Richard Harshaw rharshaw2@xxxxxxx

I meant to ask on my reply, Tom, does that same suggestion about seeing
degradation apply to the open desert at night?


Dick,

That has been my experience at Vekol, where I have observed the largest
number of nights.  I have also noticed the easterly wind shift and degraded
seeing as far from the high terrain as Sentinel.

If you can find a site that's only hundreds of feet above the basin, that
helps the seeing a lot.  Unfortunately, that also leaves you more exposed
the prevailing southwest wind.  At the same time that we recorded
temperatures in the 20's at Five Mile Meadow one year, a thermometer at the
Discovery Channel Telescope site on a small hill a few miles away recorded
a low in the upper 40's.  The DCT site does not have the problem with cold
air drainage pouring into their site, so the seeing stays stable -- most
the time sub-arcsecond -- for the entire night.

Unfortunately, the hilltop sites with good seeing are almost always
inaccessible or impracticably small for star parties.

Tom

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