Wizard Nebula

[AndyG]

Here's an image of the Wizard Nebula, NGC 7380 in Cepheus, taken with narrowband (H-alpha, S-II, O-III) filters during moonlight hours. The result is a "mapped color" image:



I also acquired some RGB image data and have been trying to learn how to overlay the more natural looking RGB stars onto the Narrowband nebula image. The technique involves removing the stars from the narrowband image before adding the RGB stars. Here's an animation of both phases of the process.

[Chuck]

Great image Andy. Just curious though, why couldn't the stars from the RGB images be added to the narrowband image w/o having to remove them first? Is it because you wouldn't be able to get the color balance right? I've thought about trying to image this myself, but w/o guiding capability at the moment, my next target will be M33. Thanks for sharing. ---- Chuck

[Apollo XX]

Way cool object, Andy! Another serious visual observing challenge if we ever get to really dark skies when Cepheus is high in the sky.

[Bruce D]

Beautiful image Andy!

[AndyG]

Thanks for the comments, guys!

Just curious though, why couldn't the stars from the RGB images be added to the narrowband image w/o having to remove them first? Is it because you wouldn't be able to get the color balance right?

The few examples I looked at recommended removing the NB stars, so I just went with that. The difficult part is the area around the stars where you are blending the NB and RGB, and I was already struggling with that. I guess if the NB background had NB star pixels and not "nebula" pixels it might have been even more difficult -- or maybe not. It would be interesting to try it to see what happens though.

[Stargrrl]

Gorgeous Andy and an object I don't think I've seen photos of before. For us astrophoto novices, is the dual color of yellow-blue the result of the type of filter applied? Or two main types of gas?

I found out also that it was discovered by Caroline Herschel!


Rebekah

[AndyG]

Thanks Rebekah!

For us astrophoto novices, is the dual color of yellow-blue the result of the type of filter applied? Or two main types of gas?

... it's both!

tldr; Yellow areas (red+green) represent areas of strong Sulfur and Hydrogen emission. Blue areas represent strong Oxygen and weak Hydrogen and Sulfur emission.

Each of the three narrowband filters passes a narrow band of wavelengths associated with a specific spectral emission line commonly present in emission nebulae. Hydrogen-alpha at 656 nm, Sulfur-II at 672 nm, Oxygen-III at 498 nm. O-III is in the blue-green part of the visual spectrum and both H-a and S-II are in the red. The result of exposing through a single filter is a monochrome image showing the strength of that emission line and hence the presence of the element in the nebula.

To make a composite color image the three monochrome images are mapped to R, G, and B color channels. This part is purely aesthetic, not scientific, since the channels can be mapped in any way you please to produce whatever colors you want. I tend to follow the convention used in many narrow-band mapped color images based on the original "SHO" or "Hubble" palette where Red = S-II, Green = Ha, Blue = O-III.

I found out also that it was discovered by Caroline Herschel!

She was amazing. I was just reading about her in Alan Hirshfeld's book, Parallax (highly recommended!)

[Stargrrl]

Thanks Andy, I appreciate the explanation! It's certainly interesting how different parts of the nebula could have such a markedly different gas composition. Rebekah

[NGC7000]

Wow! Stunning image, Andy. Great one.

Tom