Messier 94 (M94)

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June 6, 2023

Messier 94 (M94) is a spiral galaxy located in the constellation Canes Venatici. It’s about 16 million light years from us and has two rings. The inner ring structure is about 5,400 light years wide, and the outer ring is about 45,000 light years across. The outer ring contains more than 20% of the galaxy’s mass. There is a lot of star formation occurring occurring in this galaxy, particularly in the central region. There are numerous other little galaxies in the image, but I didn’t find any of them in the catalogues that I had readily available.


Acquisition, focusing, and control of Paramount MX mount with N.I.N.A., TheSkyX and PHD2. Focus with Optec DirectSync motor and controller. Equipment control with PrimaLuce Labs Eagle 3 (2021) and 4 (2023) Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Average transparency and seeing. Data acquired May 24-29, 2023 in a nearly moonless sky.

Luminance: Sky-Watcher Esprit 150 f/7 refractor and QHY600M camera with Optolong UV/IR filter
Chrominance: Takahashi FSQ-106 ED IV @ f/5 and QHY367C Pro one-shot colour camera with Optolong UV/IR filter

231 x 5m Lum = 19hr15m
234 x 5m chrominance = 19hr30m
Total: 38hr45m
Image scale 0.72 arcsec per pixel (based on Luminance)
Finder Chart 
Data Reduction and Linear Processing

Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, local normalization and integration of all frames.

Alignment of Master Frames: DrizzleIntegration was applied to the OSC frames (within WeightedBatchPreProcessing), and the result was aligned to the Luminance master with StarAlignment. This yielded aligned Lum and Colour masters.

Gradient Removal: DynamicBackgroundExtraction was applied to both masters.

Colour Calibration:  SpecrophotometricColorCalibration was used to calibrate the OSC master.

Deconvolution: BlurXterminator was used on each master with a custom psf FWHM determined with the PSFImage script, and star sharpening set to 0.10 with “Correct First” selected.

Linear Noise Reduction: NoiseXterminator was applied to each image with settings Amount=0.9 and Detail=0.15

Stretching:  HistogramTransformation was applied to each image to make a pleasing yet bright image.

Nonlinear Processing
Luminance addition: LRGBCombination was applied to replace the lightness of the RGB image with the Luminance master.

Star Removal:  StarXterminator was used to remove the stars, with Unscreen selected

Nonlinear Noise Reduction: NoiseXterminator was used to reduce noise in the background areas of the image with settings Amount=0.9 and Detail=0.1 

Contrast Enhancement: Using a mask to select the galaxy, LocalHistogramEqualization was applied twice.  A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 40, strength 0.35; scale 150, strength 0.25).

Sharpening: The same mask was used with MultiscaleMedianTransform to sharpen Layers 1 – 5 with strengths of 0.01, 0.03, 0.05, 0.05, and 0.03, respectively. 

Star Restoration: PixelMath expression combine(starless, stars, op_screen())  was used to combine the starless and stars-only images created with StarXterminator.

Final Steps: Background, galaxy and star brightness, contrast and saturation were adjusted in several iterations using CurvesTransformation with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. Image was annotated with the AnnotateImage script. Finder chart was made using the FindingChart process.