Eh, it's just stars, how hard can that be to process? If you've processed a globular cluster before maybe this list will sound familiar:
- How to show the brightness of the core without losing color saturation?
- How to deal with the faint little yellow and blue stars blending into green colors?
- How to shrink stars that are so close together without them starting to connect?
- How to maintain the feel of a globe while doing a non-linear stretch?
- Lastly a new one - how to deal with RR Lyrae variable stars that are changing brightness so quickly that you have different magnitudes with each of your color filters!
About that last point; there is a star that in the final image is decidedly green and another that is on the green side of cyan. I looked them up in Aladin and both are RR Lyrae variables which are common to see in globular clusters.
From
https://astronomy.swin.edu.au/cosmos/r/RR+Lyrae#:~:text=RR%20Lyrae%20are%20variable%2C%20horizontal,their%20size%20to%20periodically%20change.:
- RR Lyrae are variable, horizontal branch stars with periods ranging from a few hours to 2 days, and optical brightnesses that typically vary between 0.3 and 2 magnitudes. They lie in the instability strip of the Hertzsprung-Russell diagram and suffer instabilities that cause their size to periodically change. This change in size also changes the temperature of the star giving rise to their variability.
- RR Lyrae are low metallicity (population II) stars that begin their lives with a mass and size similar to that of our Sun. They become RR Lyrae stars during the red giant phase, late in the evoluton of the star, and so have typical ages of around 10 billion years. For this reason, they are generally found in globular clusters, as well as the bulge and halo of the Milky Way.
My subs tended to be shot in blocks over different nights, meaning that it's entirely possible that the stars were brighter while I shot green and dimmer while I shot red and blue. Certainly, a green star is an artifact and I could go in an manually change the color but I don't know what to change it to! So I'm leaving them in.
And given how quickly these things change color the only way to deal with I can think of is to use an OSC camera!Weird stars aside, My goal with this image is to convey the awe inspiring number of stars one can see in one glimpse. "So many stars" is what one always thinks when looking at a globular in an eyepiece. Since this is the king of GCs, I really wanted that experience in the photo.
I did use BlurX, but only to reduce stars very lightly. Sharpen Non-Stellar was turned down to 0 and Sharpen Stars was set to .19.
Thanks to
@Steeve Body for prompting me to try GHS to keep the stars from saturating while stretching.
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