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The Rosette Nebula is one of the iconic deep sky objects of the deep sky. It’s also the official state astronomical object of Oklahoma. We both learned something new today!

This was my first narrowband image using hydrogen alpha, oxygen III and sulphur II filters and though I was expecting a steep learning curve based on what I have experienced in the past, this turned out to be somewhat easier to process!

Being a narrowband image this is a false color image. The nebula does not have these colors in reality but the blessing and curse of narrowband data is that you can put it together in various ways to express yourself creatively. In my case I put 80% H-A and 20% SII in red, 20% H-A, 40% SII and 20% OIII in green and 100% OIII in blue. This produced a quite different color palette than the conventional Hubble palette but one that I found visually pleasing and seemed to visually create a sense of energy around the nebula. Whether other viewers will see it that way, I don’t know, but I figured it was worth a try.

Data acquisition was over four nights. All the exposures were 5 minutes long and I ended up with 56 H-A, 56 OIII and 58 SII for a total of just over 14 hours of integration. Thanks to the contrast created by the narrowband filters the amount of processing for this was fairly minimal.

For each master file I ran:

• Mure Denoise
• Dynamic Background Extraction

The DBE may not have even been needed. The gradients were very light, especially compared to my broadband images from this location.

I combined the images using Pixel Math using the percentages listed above. Next I ran Background Neutralization and then stretched the image using Histogram Transformation. Then, using a range mask to isolate the nebula, ran two iterations of local histogram equalization (each at a different scale). Next, I did a final curves adjustment for contrast and saturation. The final steps were the Dark Structure Enhance and AdvSharpening scripts.

The result is what you see before you. Overall, I’m pretty happy with this for a first attempt!

You can find the image as astrobin.