by Ann » Sat May 12, 2012 9:05 am
Splendid resolution. Disappointing color. Well, the ESA/HEIC images are almost always like that: they are the product of exposures through two filters, one infrared and one visual, and the colors you can tease out of a combination of such exposures are quite uninteresting. Geckzilla complained about this when she was processing Hubble images.
Fortunately, however, the ESA/HEIC page links to a picture where NGC 2366 has been imaged through two visual filters, one red and one blue. Combined with an exposure through an infrared filter, that produces an interesting image, colorwise. Check it out
here. The very red star you can see at far right in the widefield image is AA Cam, a hugely infrared star which may be about 500 times as bright as the Sun in visual light. As for the galaxy NGC 2366 itself, it looks really quite blue here, as you can see.
Why is it, though, that the emission nebulae don't look red in this picture either? The reason is probably that the red filter used for the image wasn't a narrowband filter centered at 656 nm, but a much more broadband filter, which is nowhere near as good at detecting the red Ha light of an emission nebula as a narrowband filter will be. Also the emission nebulae may well contain reflected blue starlight, and they contain blue-green Hβ light, too. Considering all the blue light you find in and near a bright star formation region, and with the filters used and balanced for the image the way they were here, the emission nebulae came out blue in this picture.
Fascinatingly, you can see one orange spot in the otherwise very blue galaxy seen in the groundbased image. I wonder what that orange spot could be. There is clearly an orange foreground star at about that spot, but there is also, to the lower right of the foreground star, a fuzzy round orange area. Is it possible that the fuzzy orange area is the center, the mini-mini-bulge of NGC 2366? All things considered, I guess it's more likely that the orange spot seen in the groundbased image is the foreground star instead.
Ann
Splendid resolution. Disappointing color. Well, the ESA/HEIC images are almost always like that: they are the product of exposures through two filters, one infrared and one visual, and the colors you can tease out of a combination of such exposures are quite uninteresting. Geckzilla complained about this when she was processing Hubble images.
Fortunately, however, the ESA/HEIC page links to a picture where NGC 2366 has been imaged through two visual filters, one red and one blue. Combined with an exposure through an infrared filter, that produces an interesting image, colorwise. Check it out [url=http://spacetelescope.org/images/heic1207b/]here[/url]. The very red star you can see at far right in the widefield image is AA Cam, a hugely infrared star which may be about 500 times as bright as the Sun in visual light. As for the galaxy NGC 2366 itself, it looks really quite blue here, as you can see.
Why is it, though, that the emission nebulae don't look red in this picture either? The reason is probably that the red filter used for the image wasn't a narrowband filter centered at 656 nm, but a much more broadband filter, which is nowhere near as good at detecting the red Ha light of an emission nebula as a narrowband filter will be. Also the emission nebulae may well contain reflected blue starlight, and they contain blue-green Hβ light, too. Considering all the blue light you find in and near a bright star formation region, and with the filters used and balanced for the image the way they were here, the emission nebulae came out blue in this picture.
Fascinatingly, you can see one orange spot in the otherwise very blue galaxy seen in the groundbased image. I wonder what that orange spot could be. There is clearly an orange foreground star at about that spot, but there is also, to the lower right of the foreground star, a fuzzy round orange area. Is it possible that the fuzzy orange area is the center, the mini-mini-bulge of NGC 2366? All things considered, I guess it's more likely that the orange spot seen in the groundbased image is the foreground star instead.
Ann