Messier 94 - The Croc’s Eye Galaxy in LRGB
Date: June 19, 2021
Cosgrove’s Cosmos Catalog ➤#0075
Messier 94 - The Croc’s Eye Galaxy (click image for full resolution via Astrobin.com)
Awarded Flickr “Explore” Status June 21, 2021
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About the Target
Messier 94 is also known as NGC 4736 and has at least two common names: "The Cat's Eye Galaxy" and "The Croc's Eye Galaxy", the latter of which seems more popular these days. This galaxy is located 16 Million Light Years away in the constellation Canes Venatici (The Hunting Dogs).
This galaxy is classified as barred-spiral and is known to have two rings systems. Messier-Objects.com describes them like this:
"A popular target for astronomers, the brighter inner part of the face-on galaxy is about 30,000 light-years across. Traditionally, deep images have been interpreted as showing M94’s inner spiral region surrounded by a faint, broad ring of stars. But a new multi-wavelength investigation has revealed previously undetected spiral arms sweeping across the outskirts of the galaxy’s disk, an outer disk actively engaged in star formation."
This is a very unusual galaxy in that there seems to be a compact core, a bit of a gap, and then a faint shell of gas and stars around it. The outer shell is very faint and I really wished I had at least double the number of exposures to maximize the quality of this faint structure.
About the Project
I recently had two nights where the skies were clear and I was available. Given that my driveway is surrounded by trees and that I can only see an object at most for 3 hours on a given night, I would have typically done at least three nights on this. However, the weather and the Moon were limiting me to these two nights.
These were shot with my Astro-Physics 130mm Starfire f/8.35 APO Refractor. This has the longest focal lengths of all of my scopes and it tends to get used for small targets like galaxies. I also have the new ZWO ASI2600MM-Pro camera mounted on the scope. The larger sensor and the higher resolution, are again, helpful with small galaxies.
Knowing my time would be limited, I shot more Lum filter subs than R, G, or B filter subs. The Lum filter is very broadband in nature - letting light in from the edges of infrared all the way to the edges of UV. This means the Lum filter just collects more light. So I ended up with 72@90 second frames for L, and 40@90 second frames for R, G, & B. When processed, my Lum image is set up to be the main image that captures fine and faint details. The color images are set up to manage noise and bring in the color without needing to drive the greatest detail. When combined, I can get an image that has the detail and contrast from the Lum image along with the color of the RGB images - the best of both worlds!
I kind of like the fact that this galaxy looks a little different than many others I have shot. It's fun to read more about your target and learn what is known about it - or even better - seeing an image of it taken by the Hubble Space Telescope (which I would grudgingly admit *might* be just a shade better than mine….8-)…..
The Annotated Image
An annotated version of M94 - created using Pixinsight’s Imagesolver and AnnotateImage scripts.
The Location in the Sky
IAU/Sky & Telescope Chart of the Constellation Canes Venatici with M94 indicated by the yellow arrow.
More Information
Wikipedia: Messier 93
Capture Details
Note on Gain:
- The first night the gain used was 0.0
- The Second night the gain used was 100.0
I could say this was done as an experiment to blend the superior dynamic range of the 0 gain setting with the greater sensitivity of the 100.0 gain setting. But the truth is that I just screwed up (SAA: Stupid Astrophotographer Actions) . I used the Grouping Keyword feature of WBPP2.1 in Pixinsight to apply the right calibration files for each night.
Light Frames
72 x 90 seconds, bin 1x1 @ -15C, ZWO Gen II L Filter
40 x 90 seconds, bin 1x1 @ -15C, ZWO Gen II R Filter
40 x 90 seconds, bin 1x1 @ -15C, ZWO Gen II G Filter
40 x 90 seconds, bin 1x1 @ -15C, ZWO Gen II B Filter
Total of 4.8 hours
Cal Frames
30 Darks at 90seconds, bin 1x1, -15C, gain 100
30 Darks at 90 seconds, bin 1x1, -15C, gain 0
30 Dark Flats at Flat exposure times, bin 1x1, -15C, gain 0
30 Dark Flats at Flat exposure times, bin 1x1, -15C, gain 100
Flats done separately for each evening to account for camera rotator variances:
30 L Flats @ gain 100
30 R Flats @ gain 0
30 R Flats @ gain 1000
30 G Flats @ gain 0
30 G Flats @ gain 100
30 B Flats @ gain 0
30 B Flats @ gain 100
Capture Hardware
Scope: Astrophysics 130mm Starfire F/8.35 APO refractor
Guide Scope: Televue 76mm Doublet
Camera: ZWO AS2600mm-pro with ZWO 7x36 Filter wheel with ZWO LRGB filter set,
and Astronomiks 6nm Narrowband filter setGuide Camera: ZWO ASI290Mini
Focus Motor: Pegasus Astro Focus Cube 2
Camera Rotator: Pegasus Astro Falcon
Mount: Ioptron CEM60
Polar Alignment: Polemaster camera
Software
Capture Software: PHD2 Guider, Sequence Generator Pro controller
Image Processing: Pixinsight, Photoshop - assisted by Coffee, extensive processing indecision and second-guessing, editor regret and much swearing…..
Adding the next generation ZWO ASI2600MM-Pro camera and ZWO EFW 7x36 II EFW to the platform…