From: Alan Friedman <alan@greatarrow.com>

Date: November 30, 2007 10:31:06 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] First light ... Mars

I think I've determined tthe following rule of thumb: moments of good seeing occur when you sleep - so just don't do that and you're all set.

Seriously - the weather tools (Clear Sky Clock included)  seem to be much better at predicting poor seeing than good. Steady  seeing is a very transient event in mid - northern latitudes, often measured in seconds rather than minutes. One of my reasons for moving to a larger chip camera was the frustration encountered in making mosaics with the 21BF04 - finding one half of a crater sharp and the other mush due to the change in stability during the time it took to move the camera. When imaging an object below 40 degrees in altitude, as it passes above the rooftops in the adjacent houses, I can almost pinpoint the energy loss for the homeowners as I watch the onscreen image respond to the various heat leak distortions.

I wish I could say that the joy is in the hunt for those magic moments... but it is a cold and tiring job setting up the scope night after night only to put it away with nary a frame collected.

cheers,

Alan

On Nov 30, 2007, at 11:54 AM, Milton Aupperle wrote:

Hi Jim;

Nice image.

I was out after Mars last night for about 1.5 hours when it was -17°C
(light cross winds so it was about -20 to -25°C on exposed flesh) but
the sky was clear and will be the only clear skies I get this week.
The scope sits outside on the balcony under a barbecue grill cover
and is always in equilibrium with the outside air.

According to the 300 mb plot and clear sky clock, i should have had
seeing that was 4/5 or better - however it wasn't even close. I had
turbulence that moved the disk +/- 5 arc seconds and sporadic bursts
of motion that turned mars into a 30 arc second boomerang or even a
50 arc second donut. This was imaging at 9 ms exposures at prime
focus of 2000 mm. Even visually stars were soft little balls due to
turbulence and instead of pinpoints, they were tiny. As I moved my
cameras and laptop back inside, I decide to have a quick peak and M42
for this year, as it rises majestically over the newly xmase
decorated 20 story crane that now blocks the only remaining view to
the south.

What I'm doing from now on is to try and quantify what factors
produce "good seeing" here. So I grab snaps of the predicted
turbulence and where the jet stream is, then take some movies of a
bright star and record my visual observations. I hope I can then get
a better handle on what factors "point" to good seeing here.

TTYL..

Milton J. Aupperle

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