After months of galaxies with a few star clusters thrown in, it is nice to get some nebulae! Thesis Barnard 145, a dark nebula in Cygnus. A dark nebulae is region of space where dust blocks the light behind it making a dark spot in the sky.

Normally we would do these as a purely broadband image but it was clear there was a lot of hydrogen gas behind the nebula and I wanted to see what using the image from the hydrogen alpha filter as a luminance layer would do. I had the (naive) thought that this would be easier to process than the LRGB image the team would normally get on this telescope/camera combination. I was right that all that faint hydrogen showed up much more in the hydrogen alpha filter but combining that with the RGB turned out to be, well, more challenging than I expected.

After a few iterations, I ended up with what I thought was a good mix or H-a and RGB but then the question was what to do about the stars. Normally, my inclination is to tone the stars down but in an image like this the stars. show the outline of the dark nebula by their absence and since this is a very dense star field, I felt it needed all those stars. It took a few iterations to find the right balance between stars and background. I wanted that hydrogen to show through clearly but I also wanted the dark nebula to be clearly defined. This balance worked for me.

I can’t say much about the nebula itself. I can’t find any reference data on it. It’s in Cygnus. It’s a dark nebula. Now you know as. much as I do

If you would like all the technical details, see astrobin.