The Crab Nebula is a fascinating object. The original nova that created the nebula was observed in 1054 AD and it resulted in a neutron star at the center rotating at 30 times per second. It is also one of the brightest X-ray sources in the sky. The Crab lies at a distance of roughly 6,500 ly and it spans about 10 ly across.

For the last several years I've tried to get a good image of the Crab nebula and I've found it to be elusive. I was under prepared in my early attempts and I didn't take seriously enough the level of precision needed to get a good image. The Crab is pretty small and it contains a lot of detail so it requires good seeing, perfect focus, and excellent guiding. Last year, I ran into problems with weather that limited the amount and quality of data that I could collect and I was never very happy with the result. Now that I'm operating in a remote, dark location with an abundance of clear skies, the challenge became trying to get enough data with sufficient quality to reveal the necessary detail and color in the Crab. In some sense, this became an exercise in lucky imaging except that each sub was 20 minutes long. I had to take a LOT of data and do a lot of filtering to come up with enough high quality subs to reach the level detail that I was looking for. I took a total of 285 subs (about 95 hours) and only 20.4% of that data was better than the 2.1" FWHM threshold that I set for this image. Poor seeing and wind induced vibration took the largest toll on my results. (The large dew-shield that I currently have on the scope really amplifies problems with the wind so I may remove it.)

This image is an LRGB image combined with 40% Ha and 30% O3 to enhance some of the structures a bit. I used the PhotometriceCalibration tool in PI to calibrate the colors, but the addition of Ha and O3 threw off the colors in the nebula. I used a straight RGB combination as a guide to remix the colors to approximate the "correct" colors in the final image. I might be able to get a better image with a 14" scope but it would be pretty hard and I'd need some really exceptional seeing. Maybe someone using short subs with lucky techniques might do it and I'd love to see how that approach would work out.

As always, C&C is welcome so let me know what I got right and what I might have screwed up.

John