Catching up.....M13

Always a favorite object, the great Hercules cluster, M13. This is probably the longest exposure I've made, about 40 minutes each channel. I was taken the morning of April 3, 2020, just before closing the observatory. That night, I let the scope run all night, with somewhat variable results. Unfortunately, this one looks to me to have a green color cast, which is indicative of light pollution. Not surprised by that. But, other than that, it seems to be one of the better images of it I have to date. I would usually take this image much later in the year; taking it in the early morning is the reason I got it now.

M13

Extra

Also on the night of April 2-3, 2020 I imaged the galaxy pair M65 and M66. I questioned whether I would be able imaged it through the high cloudiness, and it did present a problem. As with clouds, 3 of the channels did not have as much problem and 1 did; the blue channel. While all this happened as I was sleeping, more or less, there is some evidence I can show below that leads me to that conclusion.

Same image in different channels, process identicaly.

The image above is a composite of part of the green channel and the same part of the blue channel. As you can see, the sky background is much lighter in the blue channel than the green. I think that's a cloud passing over. Looking more closely, the edges of the galaxy are softened, which also occurs when viewing through a cloud. When I use one of my 2 normal processing routines, the overall “blueness” becomes vividly apparent.

Image process "normally"

After giving it some thought, I decided to try Nebulosity's “match histogram” function on the ready to “LRGB combine” frames. (Usually, I calibrate the images, stack each channel, align all channel, and end up with 4 images to use for the LRGB Synthesis function. So, in this case, 40 separate images become 4 images, then synthesized to one color image.) My goal was to decrease the blue in a more uniform way than I otherwise could. This is the result.

Histogram corrected color channels. This one is a little closer to correct, maybe.

All in all, I think it turned a lemon into lemonade. I think I worked fairly well.