[AZ-Observing] Re: Tonight
- From: Jeff Hopkins <phxjeff@xxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Fri, 23 Feb 2007 17:36:25 -0700
Tom,
You are welcome. If you have any other areas of confusion, just let
me know and I will try to help. Perhaps if you get into this you my
even be able to do some real astronomical science.
BTW, it is interesting to note how you calculated the power of a 12
mm eyepiece without knowing the focal length. Actually the 12 mm
eyepiece on my 12" LX200 GPS at F/10 is closer to 250 power.
It has been my observations that with unsteady skies the photometric
data have a large spread, Standard deviations are sometimes up to
0.05 magnitudes or worse. It is true on nights of poor transparency
that photometry can still be very good, however.
Jeff
At 14:08 -0700 02/23/2007, Tom Polakis wrote:
>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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Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
www.hposoft.com
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