Re: What's the effect of imaging through jet stream?

Mike Shade

Consistent problems suggest hardware problems, polar alignment, PEC curve issues, flexure, poor guiding parameters, this sort of thing in that they impact everything consistently.  Unusual or rare problems like you are sharing suggest transient issues the most likely being seeing.  I work with a 17" telescope at .63"/pixel, I know how seeing can ruin things.  If the system returns consistent results and then all of a sudden doesn't, first thought is seeing.  The fact that your stars were not messed up in one consistent direction is a clue.  I did have a time where my images were horrible all of a sudden and then get good.  Finally went out and found a rather large owl sitting on the edge of the telescope upper ring.  Luckily there was no deposit on the primary mirror.


There are numerous reference on the impact of seeing and how professionals monitor and search for sites with good seeing.


Mike J. Shade

Mike J. Shade Photography:


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International Dark Sky Association:


From: [] On Behalf Of Cheng-Yang Tan via
Sent: Saturday, May 30, 2020 10:53 AM
Subject: [ap-gto] What's the effect of imaging through jet stream?


Hi guys,
   Hopefully my question is not off topic. But here goes:

   I imaged M101 last night (alt at 76 deg and close to the meridian) with my Mach1GTO and I had to throw away 1/2 my subframes. I examined the bad subframes and there's no consistent direction for the eggy stars from each subframe. Some subframe's eggy stars were in RA direction, some were in DEC direction and some were angled w.r.t. RA and DEC. I looked at the meteoblue seeing map (attached) and it says that the jet stream was at around 31 m/s last night. PHD2 guide graph was about 0.5 arcsec rms error for the entire night which wasn't too bad for the entire session because my image scale is 2.1 arcsec/pixel.

Is the above something that I'd expect imaging through the jet stream? Or I should be looking for something else to blame like flexure?

Thanks (before I start tearing everything apart :) )


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