[AZ-Observing] Re: Tonight
- From: Tom Polakis <tpolakis@xxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Fri, 23 Feb 2007 16:08:41 -0500
Jeff,
Thanks for the photometry information. Since I am unfamiliar with photometry,
I wonder if you could achieve the photometric stability that you quantified
from last night's run even if the seeing were poor. The "fast" seeing that
we've been discussing does not result in much "flickering" as much as it just
increases a star's "blur" (for lack of a better terms). So it seem like over
the course of the integration time required for your photometry, the average
brightness would be quite repeatable, as you observed.
I am familiar with visual observing, however. The fast-moving air currents
that several of us noticed last night are typically more global than local to
the site, whereas mountain drainage into basins results in slower-moving seeing
cells. So perhaps despite the excellent photometric conditions you
experienced, the seeing for visual observers was not so great even at your
site. After all, your 12mm eyepiece would yield a magnification of only 170x,
which is just barely enough to magnify the Airy discs enough notice seeing
effects.
Regarding FWHM seeing measurements, back when I was imaging from my backyard
with a 13" and ye olde ST-7 CCD camera, the values output by MaximDL software
correlated quite well with the visually observed seeing conditions. On the
best nights, I measured seeing in the neighborhood of 1.5", and it was apparent
at the eyepiece. More typically, I was getting numbers nearer to 3".
Tom
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