Casitas de Gila, NM, October 29 – 30, Gold Canyon, AZ, December 23 – 24, 2022

Since I purchased my SVX102T refractor, I have image some of the most photographed deep sky objects.  M42, the Great Orion Nebula is usually one of the first targets a new astrophotographer photographs.  It was one of my first targets with an SCT.  However, it is a challenge to image and process properly as it is both very bright and dim, requiring multiple exposure times.  For red, green and blue filters, I took multiple 15, 30, 60 and 120 second exposures over five nights.  I also captured 3nm Hydrogen-alpha filter data with 60, 120 and 240 second exposures.  M42 was the third target in New Mexico and the second target in Arizona imaged each night.  All of the data were used to construct high dynamic range (HDR) masters for each filter.

I started to process the data using a similar workflow in PixInsight as I have done with other nebulae.  However, it was indeed challenging to produce an acceptable image that preserved the bright core of the nebula and showed sufficient details in the dark clouds.  The WeightedBatchPreprocessing script (WBPP) was used to calibrate and integrate each set of subframes per exposure and filter.  Fifteen integrated master images were produced.  I failed to obtain useful HDR composites using the GradientHDRComposition tool.  So, I turned to the HDRComposition tool and adjusted the parameters as follows: binarizing threshold = 0.800, Mask smoothness = 25, Mask growth = 2.  The R, G and B composites were acceptable, but the dark clouds lacked detail.  However, the Ha composite captured sufficient details.  I combined the red, green and blue masters to create an RGB color image.  Incorporating Ha into the red channel produced an image that too red.  I saved the Ha master for luminance processing.  Background extraction (DBE or ABE) was not used as there was little sky background in the image.  I calibrated the color with the new PhotospectroscopicCalibration tool, which worked beautifully after plate solving the image.  Background neutralization was then done.

From this point, I had many problems processing the RGB image, and I had to start over several times.  I was forced to experiment with each tool selection and parameter settings.  I was excited to try BlurXTerminator on a nebula.  I used the FHWMEccentricity script to calculate a point spread function (PSF) for the stars.  However, BlurXTerminator destroyed the very small Trapezium stars leaving behind chrominance “debris”.  After many iterations, I finally ended up masking the core with a range mask to make BlurXTerminator work its magic (note: BlurXTerminator seems to honor masks).  Stretching was also fraught with problems.  I used the GeneralizedHyperbolicStretch tool in successive steps.  After the first, small stretch, I masked the core region.  The, as I stretched again, I tuned the core mask so that the core blended with the rest of the image without artifacts.  NoiseXTerminator was used to denoise the RGB image.  StarXTerminator was then applied to the stretched RGB image to remove the stars.  The stars were saturated and set aside for later processing. 

Next, I tried many different combinations of the RGB luminance and Ha master to preserve the “Running Man” while enhancing the details in the dark regions.  The combined HaLum image was then stretched using a core mask same way as the RGB color image.  The HaLum image was denoised with NoiseXTerminator and the stars were removed with StarXTerminator.  The stars HaLum image was used later.  The image was sharpened, and the contrast was enhanced with the HistogramEqualization tool run with three kernel sizes.  Both starless and stars RGB images were combined with luminance images.  The colors were adjusted and saturated.  The final starless HaLRGB nebula was combined with the LRGB stars using the PixelMath combine function with the opscreen() parameter.  Photoshop was used to fine tune saturation and sharpness in selected areas of the frame, and to crop and save as a Jpeg file.  

Messier 42, M42, or NGC 1976, the Great Nebula in the constellation Orion, is a large star forming region in Orion’s sword that is visible to the naked eye with an apparent magnitude of 4.0.  In the bright center, there is a very young open cluster, the Trapezium, with four primary stars within a diameter of 1.5 light years.  Two of these can be resolved into their component binary systems on nights with good seeing, giving a total of six stars.  The Trapezium cluster is a component of the much larger Orion Nebula, an association of about 2,800 stars within a diameter of 20 light years, spanning 24 light years (1 degree of sky).  The Orion Nebula is surrounded by the much larger Orion molecular cloud complex, which is hundreds of light years across, spanning the whole Orion Constellation.  M42 has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust.  Astronomers have directly observed protoplanetary disks and brown dwarfs within the nebula, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula.  M42 is the closest region of massive star formation to Earth, about 1,350 light years away (Wikipedia, NASA).

While the Orion nebula was known since antiquity, the first detailed observation of nebulosity was made on November 26, 1610 by French astronomer Nicolas-Claude Fabri de Peiresc.  Charles Messier observed the nebula on March 4, 1769, and he also noted three of the stars in Trapezium.  Messier published the first edition of his catalog of deep sky objects in 1774 with the Orion nebula listed as the 42nd entry.  On September 30, 1880, Henry Draper used the new dry plate photographic process with an 11-inch (28 cm) refracting telescope to make a 51-minute exposure of the Orion Nebula, the first instance of astrophotography of a nebula in history. In 1883, amateur astronomer Andrew Ainslie Common used the dry plate process to record several images in exposures up to 60 minutes with a 36-inch (91 cm) reflecting telescope in Ealing, west London.  For the first time, these images showed stars and nebula detail too faint to be seen by the human eye (Wikipedia).

Imaging details:

Stellarvue SVX102T with SFR0.74 focal reducer (FL = 528mm, f/5.2)
ZWO off-axis guider (OAG-L) with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10C)
Chroma 36mm filters:  Luminance, Red, Green, and Blue
Equatorial camera rotation: 270 deg

Software:    Sequence Generator Pro, ASTAP plate solving, PHD2 guiding, 
    Losmandy Gemini ASCOM mount control and web client interface,
    SharpCap Pro for polar alignment with the Polemaster camera,
    PixInsight 1.8.9 with StarXTerminator (AI version 10) and NoiseXTerminator,
    Photoshop CC 2022

Red    15 sec x 45 subframes (11.25 min), Gain 100, Offset 68, 1x1 binning
Red    30 sec x 45 subframes (22.5 min), Gain 100, Offset 68, 1x1 binning
Red    60 sec x 70 subframes (70 min), Gain 100, Offset 68, 1x1 binning
Red    2 min x 55 subframes (110 min), Gain 100, Offset 68, 1x1 binning
Green    15 sec x 45 subframes (11.25 min), Gain 100, Offset 68, 1x1 binning
Green    30 sec x 45 subframes 22.5 min), Gain 100, Offset 68, 1x1 binning
Green    60 sec x 65 subframes (65 min), Gain 100, Offset 68, 1x1 binning
Green    2 min x 56 subframes (112 min), Gain 100, Offset 68, 1x1 binning
Blue    15 sec x 45 subframes (11.25 min), Gain 100, Offset 68, 1x1 binning
Blue    30 sec x 45 subframes (22.5 min), Gain 100, Offset 68, 1x1 binning
Blue    60 sec x 60 subframes (60 min), Gain 100, Offset 68, 1x1 binning
Blue    2 min x 63 subframes (126 min), Gain 100, Offset 68, 1x1 binning
Ha    60 sec x 70 subframes (70 min), Gain 100, Offset 68, 1x1 binning
Ha    2 min x 55 subframes (110 min), Gain 100, Offset 68, 1x1 binning
Ha    4 min x 50 subframes (200 min), Gain 100, Offset 68, 1x1 binning

Total integration time: 17.1 hours