M1, The Crab Nebula

M1 11hr20m LHaRGB October 2014

Click image for full size version

October 27, 2014  published in Sky & Telescope Magazine, Feb. 2015 (p. 76), Astronomy Magazine Online Picture of the Day, Feb. 2, 2015

Crab NebulaThe Crab Nebula is a remnant of a supernova, or exploding star, lying about 6500 light years away in Taurus, the Bull.  The star that gave birth to M1 exploded in July 1054 AD, and was documented by people around the world.  It was visible during the day for 3 weeks.  The nebula is powered by the remnants of that explosion, a neutron star.  The tiny but massive star spins more than 30 times per second, and appears to emit pulses from gamma rays to, so is known as a pulsar.   It is the strongest persistent source of X-rays and gamma rays over 30 kEV.  There’s a good article about the Crab Nebula in the March 2011 issue of Astronomy magazines.  We are lucky to get to see it:  objects like this dissipate and fade slowly over time.Astronomy Magazine online Picture of the Day


10″ ASA @ f/6.8 on a Paramount MX.  SBIG STL-11000 with Baader LRGB and Ha filters.  Guiding with SV-80 80 mm f/6 refractor and camera’s Remote Guide Head.  Acquisition with TheSkyX.  Focusing with FocusMax4.  Scripting using CCDCommander.   All pre-processing and processing in PixInsight.  No moon for LRGB, gibbous moon for H-alpha.  Transparency and seeing  average for R, G and B and Ha and excellent for L.  Acquired from my SkyShed in Guelph, ON.   

6x10m R, 6x10m G, 5x10mB; 12x20m Ha, 27x10m L (total = 11hr20m)

The batch pre-processing script was used to calibrate, register and combine the frames.  R, G, B, L and Ha channels were cropped.

R, G and B were combined, and RGB, L and Ha were background corrected with DBE.  The NB-RGB Combine script was used to combine the Ha and RGB data (Ha scale of 8).  The resulting HaRGB file was processed with colour calibration, HistogramTransformation, ACDNR (small scale), another HistogramTransformation, and a curve to boost contrast and saturation.

The L image, which was background-corrected earlier, was processed using Deconvolution (PSF made from 40 stars using DynamicPSF), HistogramTransformation, HDRMultiscaleTransform (6 and 4 wavelet layers, masked), ACDNR (small scale), another HistogramTransformation, TGV noise reduction and LocalHistogramEqualization (only on centre of nebula).

The luminance of the HaRGB image was matched to the L image using LinearFit, and then combined back into the HaRGB image using ChannelCombine in the Lab colour space.  Then LRGBCombine was used to overlay the L onto the HaRGB.  A slight unsharp mask was applied to the centre of the nebula, and colour balance, brightness and saturation were adjusted.

The Image scale is 1.1 arcsec/pixel for this camera/telescope combination.