APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

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APOD Robot
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APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

Post by APOD Robot » Fri Feb 19, 2016 5:06 am

Image NGC 2403 in Camelopardalis

Explanation: Magnificent island universe NGC 2403 stands within the boundaries of the long-necked constellation Camelopardalis. Some 10 million light-years distant and about 50,000 light-years across, the spiral galaxy also seems to have more than its fair share of giant star forming HII regions, marked by the telltale reddish glow of atomic hydrogen gas. The giant HII regions are energized by clusters of hot, massive stars that explode as bright supernovae at the end of their short and furious lives. A member of the M81 group of galaxies, NGC 2403 closely resembles another galaxy with an abundance of star forming regions that lies within our own local galaxy group, M33 the Triangulum Galaxy. Spiky in appearance, bright stars in this colorful galaxy portrait of NGC 2403 are in the foreground, within our own Milky Way.

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Ann
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Re: APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

Post by Ann » Fri Feb 19, 2016 5:16 am

That's a lovely image! :D
M33. Photo: Oriol Lehmkuhl and Ivette Rodríguez
I was going to say that NGC 2403 closely resembles M33, but Otto Posterman - sorry, APOD Robot - pointed that out already. Well, NGC 2403 looks a little more sparkly and blue to me than dear old Triangulum galaxy.

Ah well, the difference isn't great!

Ann
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Re: APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

Post by Guest » Fri Feb 19, 2016 8:08 am

APOD Robot wrote: Spiky in appearance, bright stars in this colorful galaxy portrait of NGC 2403 are in the foreground, within our own Milky Way.
I understand where the 'spikes' around the stars come from, but I am wondering about the 'halo' or glow around them too. Is the halo the result of a) interstellar dust scattering of light (a dirty galaxy); b) scattering of light by dust in our solar system (a dirty solar system); c) scattering caused by the optics (lenses) of the viewing instrument (dirty lenses or glass impurities); or d) saturation of the optical chip around the single point sources? Or some combination of the above. And if a combination, what proportions could be attributed to each? Ideas or opinions?

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Re: APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

Post by Chris Peterson » Fri Feb 19, 2016 3:03 pm

Guest wrote:I understand where the 'spikes' around the stars come from, but I am wondering about the 'halo' or glow around them too. Is the halo the result of a) interstellar dust scattering of light (a dirty galaxy); b) scattering of light by dust in our solar system (a dirty solar system); c) scattering caused by the optics (lenses) of the viewing instrument (dirty lenses or glass impurities); or d) saturation of the optical chip around the single point sources? Or some combination of the above. And if a combination, what proportions could be attributed to each? Ideas or opinions?
From (a), none. From (b), none. From (c), some. And also from seeing effects- the wiggling of the stellar position caused by our moving atmosphere. You're on the right track with (d), but it isn't saturation. The fact that we are seeing the color of the stars even at their cores demonstrates that the data isn't saturated. But the stars are, in fact, much brighter than the galaxy. And the brighter a star, the larger its physical diameter, since we can see further out along the wings of its diffracted image.

This image was made with a high end scope, but it still has two mirrors that have somewhat rough surfaces. So what we're seeing is combination of the above mentioned diffraction, scatter off the mirrors, and internal reflections in the filters and CCD detector.
Chris

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Re: APOD: NGC 2403 in Camelopardalis (2016 Feb 19)

Post by Boomer12k » Sat Feb 20, 2016 12:08 am

Spectacular....

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