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Effect of Moon Glow
I guess that this is the sort of thing that you do when idle and waiting for the end of twilight and for an imaging run to kick off.
I was just reviewing the luminance subs that I captured of M64 from an image run on Thursday night just gone (23 May). Whilst doing so I noticed a significant brightening in the background of the subs towards the end of the imaging run. I then realised that the end of the run had overlapped with the rising of the moon which was 78% illuminated. Interesting I thought so I decided to get a bit more scientific and use a couple of methods to determine exactly how much brighter the subs were. I ran the subs through the sub frame selector tool in Pixinsight as well as taking a sample of the background ADU in each image. I then plotted the background ADU over time as well as producing a graph output from the sub frame selector tool showing the change in SNR weighting.
As you can see from the attached images, the effect of the moon glow becomes apparent approximately 30 minutes before the rising of the moon and significantly increases once the moon pops its head over the horizon. The moon was at an angular separation of about 110 degrees at the time as M64 was just past the meridian.
Needless to say, the last few subs will be going in the bit bucket.
Cheers.
Rodney.
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