Tuesday, May 3, 2016

Fog and Dew.

Last night was the best night in ages so after taking care of some commitments for the Auckland Astronomical Society I headed out to Kumeu Observatory, I was a bit discouraged when I arrived in Kumeu to see that the fog was really thick, I could barely see a few meters in front of my car even with the fog lights on! Thinking that I would show some perseverance I set about setting up, the fog was well above even the tallest trees and so thick that with the naked eye I could only see the brightest stars so after taking some test images I realized I would have to wait for the fog to thin out a bit.

The state of the Fog when I arrived at Kumeu Observatroy ^

As the temperature started to drop around midnight the fog finally started to settle down, it was still really thick in the east so I decided to start my pointing model in the west, I opted to make a really dense pointing model as I had no idea how long it would take for the fog to lift in the east, everything was going really well and I had astrometrically solved over 150 odd samples without issue until all of sudden the images would no longer solve, what turned out to be the problem was that the correcter plate on the C14 had become "fogged" up due to the dew, earlier on in the night I realized this might be an issue so I had turned on the dew strap to full power as a test to see if it would keep the dew off all night, but to my hand the strap still felt cold after hours so maybe it was never re-connected when we put the OTA back on the mount, at any rate it was not keeping the dew off at all.

Dew on the corrector plate ^

I didn't want to give up but I was also now in a part of the sky where the star density was low, so I lowered the detection threshold in T-Point and increased my exposures to 10 seconds, I then stepped to a higher up part of the sky where the effects of the fog were the least, this seem to do the trick as I managed to get up to 182 sample points, it was 3 am by this stage so after getting almost all the western side of the sky I turned the telescope towards the east, the fog had finally started to settle down a bit so I figured I might be able to continue on until dawn but as soon as I took my 1st image in the east I got hit by an error message saying that "The mount is at a minimum or maximum position limit and cannot be slewed. This error may be the result of improper synchronization near the meridan. When syncing near the meridian, be sure the optical tube assembly and the synchronization star are on opposite sides of the meridian. ".

Error message ^

I tried to continue the pointing model but the mount had become confused and attempted to point the telescope at the ground so I aborted the slew and finished and saved the pointing model before "homing" the telescope,
even though I was annoyed that I couldn't finished the pointing model I was happy with how many samples I had captured, so hopefully next time I'll get the entire sky, I tested the pointing model and found it was extremely accurate in the western side of the sky as you'd expect with every target being right in the middle of the crosshairs, the eastern side targets did not fall in the center of the frame though so a new pointing model will have to be done of course, the images at this point were pretty bad due to the dew and with no way to de-fog the corrector plate I closed up the dome and headed home around 4 am.

Pointing test of Omega Centauri ^

Pointing test of NGC 4945, image quality had really deteriorated by this stage ^

The fog had settled down a bit by early morning but as you can see it was still very foggy conditions. ^

Posted by Jonathan Green

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