M51: The Whirlpool Galaxy

M51, The Whirlpool Galaxy

M51 is also known as the Whirlpool Galaxy because of the look of the spiral shape when viewed through a telescope. It’s a fairly small target for my modest telescope but at this time of year the limited section of sky viewable from my back yard doesn’t leave many choices until late at night. It’s also something I’ve always wanted to image so despite the small size in the frame I decided to go ahead.

Technically, M51 is the larger bluish spiral galaxy and the yellower companion galaxy is NGC 5195. The galaxies are definitely interacting and this has distorted both galaxies. They are about 23 million light years away.

I have not quite 4hours of data on this so far: 70 minutes luminance, 50 red, 47 green and 50 blue. I’m hoping to get more on each filter, particularly blue but despite the relative paucity of data this wasn’t too bad to process.

Preprocessing included local normalization using a scale of 256 since 128 caused splotchy background problems.

Post Processing steps were as follows:

Luminance:
Mure Denise
Dynamic Crop
Dynamic Background Extraction
Histogram Transformation
For Each RBG:
Mure Denise
Dynamic Crop
To make the RBG:
Channel Combination
Dynamic Background Extraction
Photometric Color Calibration
LRBG
LRBG Combination (adding in luminance to RBG)
Local Histogram Equilization
TGV Denoise
Multiscale Linear Transform (sharpening)
Curves Transformation (saturation)
Histogram Transformation (black point)
Dynamic Crop

Processing was fairly straightforward.

The luminance data was collected on the night of June 21/22nd. The seeing was fairly bad and this showed up in my guiding. There were also high thin clouds that came through after I went to sleep and I ended up having to discard almost 20% of the frames. Despite the guiding woes, only a relatively small number had to be discarded due to bloated or oblong stars. At this point, M51 is only visible for about an hour each night before it goes behind a neighbor’s tall tree so for now I’m using all the R, G and B subs along with the L to “beef up” the luminance channel. Hopefully I can get more but I’ll likely need to get to some other site to get better horizons.

The RBG data was on the following night. The seeing was much better on the second night though neither night had what could be described as good seeing. Despite the relatively poor seeing the stars came out smaller than expected so there is something to be said for a relatively forgiving image scale (1.6 arc seconds per pixel). Unfortunately, my guiding still wasn’t great (though better than the night before). However, I had SGP set to discard frames where the guiding error exceeded 3.2 pixels and this happened 47 times (actually that might be between both nights). Either way I had to discard a lot of frames before they even got to disk so ended up wasn’t a lot of time.

I managed to get more blue data on July 9th but it was headed toward the tree when the blue channel finished. I’m hoping for more but depending on the weather this might be it for the season.

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