by Ann » Sat Aug 10, 2024 5:10 pm
As Christian surmised, I'm not too happy with the non-blue appearance of the blue hue of the reflection nebula part of the APOD.
Let's compare the APOD with a picture that I like very much myself:
As you can see, the colors of Emmanuel Astronomono's picture are much more saturated than the colors of the APOD. For myself, I'm okay with a pale pink hue of the central emission nebula, but I definitely want a bluer version of the reflection nebula than what the APOD offers. To me it barely looks blue at all. Indeed, at first I didn't even realize that I was looking at the Trifid Nebula!
If you go to Robert Edelmaier and Gabriele Gegenbauer's
website, you can see that they used not only RGB filters for their image, and not just RGB + Hα filters either, but RGB + Hα + OIII + SII filters. There is no way that you are going to get a good RGB color image from the use of all those filters. If all the filters have been used to detect nebulosity, then we must be dealing with a false color (or, as Chris would say, a mapped color) nebula.
We should note that the reflection nebula in the APOD is definitely larger (and also brighter) than the reflection nebula in Emmanuel Astronomono's image. My guess is that one or more of the narrowband filters have detected nebulosity at a larger distance from the central Trifid than RGB filters typically do. It wouldn't surprise me at all if some of the outermost nebulosity in the APOD is faint red SII.
We are definitely seeing much more red Hα than we usually do in the vicinity of the Trifid, at upper right and lower right.
In any case, the visually blue reflection nebula has been mixed with colors detected by narrowband filters, and the image has been processed so that the reflection nebula is a pale shade of gray, even beige.
An interesting aspect of the APOD is that the pink emission nebula looks smooth, whereas the "blue" reflection nebula looks extremely tousled, like a poor cat's or dog's wildly unkempt fur. Of course, the pink emission nebula gets its color from ionized hydrogen, whereas the reflection nebula gets its color from billions of tiny grains of dust which are certainly "blowing in the wind".
I find the APOD irritating but interesting.
Ann
As Christian surmised, I'm not too happy with the non-blue appearance of the blue hue of the reflection nebula part of the APOD.
Let's compare the APOD with a picture that I like very much myself:
[float=left][img3="The Trifid Nebula. Credit: Image Credit & Copyright: Robert Edelmaier and Gabriele Gegenbauer"]https://le-cdn.website-editor.net/s/776ab31444b54f92ac26f7da5c0aa074/dms3rep/multi/opt/M+20+LRGBHaO3S2+jpg-1920w.jpg?Expires=1725638528&Signature=cK8DAmIhha3cubrxsXWG4D1KD4eMgBwt4C3PJeJa0stPW-2rffsOk471--JoBgQw7PUd7tVuxDSOdYcUfRnXNw3Tg43VS0MFxdMoxE0lbNAn~w5ac6comTlgW9Xaypav4TtTmfP27uR9iWbG6pXGQeRovO4Pyyi~Iq5FV~SSSuOeHrr5XyT1tpS-VfYFYP-Ht98Id~R9zOW3w3c8hwMctuPsm-dWPleuzoSTOWnzJMws8vXfxyHhgeBeHlCumioFxVQ9cYIHpmHUkyClSN~414kZnzsjwl8~pV2Mbqda27mqRRjRerPsmxATnm7acV3gvJrKREf3yKSkKBFRQxthFg__&Key-Pair-Id=K2NXBXLF010TJW[/img3][/float][float=right][img3="The Trifid Nebula. Credit: Emmanuel Astronomono"]https://dq0hsqwjhea1.cloudfront.net/sandt-1.jpg[/img3][/float]
[clear][/clear]
As you can see, the colors of Emmanuel Astronomono's picture are much more saturated than the colors of the APOD. For myself, I'm okay with a pale pink hue of the central emission nebula, but I definitely want a bluer version of the reflection nebula than what the APOD offers. To me it barely looks blue at all. Indeed, at first I didn't even realize that I was looking at the Trifid Nebula!
If you go to Robert Edelmaier and Gabriele Gegenbauer's [url=https://www.astropicture.at/skandinavien]website[/url], you can see that they used not only RGB filters for their image, and not just RGB + Hα filters either, but RGB + Hα + OIII + SII filters. There is no way that you are going to get a good RGB color image from the use of all those filters. If all the filters have been used to detect nebulosity, then we must be dealing with a false color (or, as Chris would say, a mapped color) nebula.
We should note that the reflection nebula in the APOD is definitely larger (and also brighter) than the reflection nebula in Emmanuel Astronomono's image. My guess is that one or more of the narrowband filters have detected nebulosity at a larger distance from the central Trifid than RGB filters typically do. It wouldn't surprise me at all if some of the outermost nebulosity in the APOD is faint red SII.
We are definitely seeing much more red Hα than we usually do in the vicinity of the Trifid, at upper right and lower right.
In any case, the visually blue reflection nebula has been mixed with colors detected by narrowband filters, and the image has been processed so that the reflection nebula is a pale shade of gray, even beige.
An interesting aspect of the APOD is that the pink emission nebula looks smooth, whereas the "blue" reflection nebula looks extremely tousled, like a poor cat's or dog's wildly unkempt fur. Of course, the pink emission nebula gets its color from ionized hydrogen, whereas the reflection nebula gets its color from billions of tiny grains of dust which are certainly "blowing in the wind".
I find the APOD irritating but interesting.
Ann