Moonstruck, Part II

December 5-6. Another clear, moon-filled night. The sky is bluer tonight than last; more moisture perhaps?

I lost an hour I could have used imaging the Veil to an utter inability to calibrate the guider. Turned out that the mount had been rotated (somehow, somewhen?) a good 15 degrees west of the pole, so the RA drive was interfering with DEC offsets and introducing a fast set in RA, too. I lined up on the pole, roughly, and all was instantly solved with that.

The shim that insures that the CCD is installed in the same orientation (long side parallel to the RA axis) is just a whisker too thick. It forces the SBIG a little out of perpendicular to the optical axis of the 200mm. Stars on the west side of each frame are softer than stars 2/3rds the way across the field. There is a zone of beautifully focused stars, then slightly softer ones again. The CCD is slightly tilted with respect to the focal plane. Fix this before the next clear spell.

Dew! None of the frames of the Horsehead were as vivid as yesterday's. As the night went on, I watched the Horsehead dim and sink deeper and deeper into a glowing background. I eventually found dew hazing the big L37C filter. I could have wiped it, heated it, or removed it, but the Horsehead was solidly into the trees by then, so I called it a night.

Lessons: 1) Verify polar alignment because it matters even when the auto-guider works perfectly. 2) Re-work the 200mm support in this orientation. 3) Make a dew shield -- tape and aluminum flashing is a good start. 4) Adding data from different nights is easy. 5) The sequence tab in Maxim works great!

Not one decent image, but a good night under the stars anyway.

 

Messier 42 rising through the trees.
A focus frame while lining up to add Horsehead data.
200mm EDIF, ST2000XM, 5 seconds at F2.8, 10nm H-a.

 

 

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Text & Photos by David Cortner
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