Imaging in the Wind

W Hilmo

I've been doing a bunch of experimenting to transition from guided imaging with an SCT, to unguided imaging with a first class refractor.  Coincident to this, I'm imaging in a particularly windy area, which I moved to a few months before I received my AP130GTX.  Previously, I lived in an area with lots of overcast, but little wind.  It was also sheltered by being completely surrounded by forest.  My current location is wide open and completely unsheltered from the wind.

As mentioned, the scope is an AP130GTX.  The mount is an AP1600 with Absolute Encoders.  I'm finding that on calm nights (which are rare this time of year), I get nice, round stars at 10 minutes unguided.  With our typical winds, which are around 30mph over night, I get blobby and elongated stars.  Last night was windy, so the subs were all soft, with poor eccentricity.  I'm trying to determine how much of my soft stars are the the result of turbulence higher up, versus the mount and scope getting buffeted by the wind.

When I was blinking through the subs, I found the image that I've attached below.  It's interesting because there are crossing satellite trails at very different angles, that show signs of significant vibration.  I am guessing that what is happening here, is that the system is getting buffeted by winds, and the jaggies are due to the absolute encoders trying to quickly make corrections.  But I would be interested in other thoughts.

For tonight, I'm going to image the same field, but I've parked my motorhome up wind of the mount to act as a block.  The motorhome is parked 90 degrees to the prevailing wind, and is as close as I can get it while still keeping the roof at about 20 degrees elevation from the scope.  We are forecast for similar winds tonight, and the wind today seems consistent with yesterday.  I'll be curious to see if the results improve.  I'm not sure yet if turbulence as wind goes over and around the motorhome will be more than offset by sheltering the mount.

I am planning for an observatory, and have been thinking all along of a roll-off roof.  I suppose that if tonight's data looks good, perhaps I should be thinking about a dome.  Since I'm not planning on building the observatory until next year, I am also planning on experimenting with different wind blocks (presuming I can find something less than the motorhome, which can stand up to our winds on a regular basis).

If anyone else has dealt with this, I would be interested in how people have dealt with this.  I suppose that I could switch to only wide field imaging during the windiest times of the year, but if possible, I would like to mitigate things.


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