APOD: Across Corona Australis (2018 Nov 29)

[APOD Robot]

Across Corona Australis

Explanation: Cosmic dust clouds are draped across a rich field of stars in this broad telescopic panorama near the northern boundary of Corona Australis, the Southern Crown. Less than 500 light-years away the denser clouds effectively block light from more distant background stars in the Milky Way. The entire vista spans about 5 degrees or nearly 45 light-years at the clouds' estimated distance. Toward the right lies a group of bluish reflection nebulae cataloged as NGC 6726, 6727, 6729 and IC 4812. The characteristic blue color is produced as light from hot stars is reflected by the cosmic dust. The dust also obscures from view stars in the region still in the process of formation. Smaller yellowish nebula NGC 6729 surrounds young variable star R Coronae Australis. Below it are arcs and loops identified as Herbig Haro (HH) objects associated with energetic newborn stars. Magnificent globular star cluster NGC 6723 is above and right of the nebulae. Though NGC 6723 appears to be part of the group, its ancient stars actually lie nearly 30,000 light-years away, far beyond the young stars of the Corona Australis dust clouds.

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[Boomer12k]

Interesting.... a "sheepdog" like shape, with blue eyes, and a small guy next to him doing pushups....amazing...

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[heehaw]

Our filthy galaxy.

[Leon1949Green]

Question: which direction is the 500-lightyear cloud moving? Will it sometime cover NGC 6723, or did id used to hide it before we were around? Thanks!

[BDanielMayfield]

Our filthy galaxy.

But 'from dust we are,' so it's a very good thing. Better dusty than red n dead, as galaxies go.

[Ann]

Our filthy galaxy.

But 'from dust we are,' so it's a very good thing. Better dusty than red n dead, as galaxies go.

And a bit of brown dust is what it takes to make blue stars! Better red than dead, they say, but when it comes to galaxies, red is dead!

Click to view full size image

PGC 62700 or ESO 396-16.
Source: http://astro.phym.nl/2016/09/25/dust-on ... ern-crown/

Speaking of galaxies, there is a pretty-looking one at about one o'clock, near a bit of blue fluff of nebulosity. I think that the galaxy is PGC 62700, which apparently also goes by the name of ESO 396-16.

All in all, this APOD is very much my cup of tea, of course. We've got an elongated filament of dust, exactly the kind of structure that is likely to produce stars, and the brightest stars it has given birth to are blue! And the entire skyscape is striking and varied with brand new young stars born out of dust, plus a magnificent ball of geriatric stars, plus a distant galaxy. And like Boomer said, the whole thing looks like a dog with a blue eye! The only thing that would have made it better is if it had looked like a cat.

Ann

[Visual_Astronomer]

This is an awesome picture! Must travel to the southern hemisphere some day to see the rest of the sky!

[neufer]

R Corona Australis

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[BillBixby]

R Corona Australis

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FANTASTIC. Thank you.

[Ann]

R Corona Australis

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Art, where did you find the picture at top? I would like to check it out a bit better and maybe find out who the photographer is, what filters were used for it, and what star we are actually looking at (R Corona Australis???) and how much of the nebula we are looking at here.

Could you give us a bit more info? Isn't that more or less required here?

Ann

[Ann]

Okay. I'll provide the info that Art didn't.

The source of the picture is this page. It is an ESO image, and the photographer is Sergey Stepanenko. The filters used for the image were SII and H-alpha. Optically, these two filters actually detect the same shade of red, but H-alpha represents a higher degree of ionization than SII.

The picture only covers a small part of the large nebula seen in the APOD, although the third picture that Art provided made that pretty clear.

Ann

[Chris Peterson]

Okay. I'll provide the info that Art didn't.

The source of the picture is this page. It is an ESO image, and the photographer is Sergey Stepanenko. The filters used for the image were SII and H-alpha. Optically, these two filters actually detect the same shade of red, but H-alpha represents a higher degree of ionization than SII.

Singly ionized sulfur (S II) produces a doublet, at 671.6 and 673.1 nm. H-alpha produces a line at 656.28 nm. They are close, and many narrowband filters are wide enough to pass both. But they are definitely different shades of red, and an imager who uses filters for both will certainly be using narrow enough bandpasses that the two are distinctly separated, and can be mapped to different colors in post processing in order for the two atomic species to be clearly distinguished.

[Ann]

Okay. I'll provide the info that Art didn't.

The source of the picture is this page. It is an ESO image, and the photographer is Sergey Stepanenko. The filters used for the image were SII and H-alpha. Optically, these two filters actually detect the same shade of red, but H-alpha represents a higher degree of ionization than SII.

Singly ionized sulfur (S II) produces a doublet, at 671.6 and 673.1 nm. H-alpha produces a line at 656.28 nm. They are close, and many narrowband filters are wide enough to pass both. But they are definitely different shades of red, and an imager who uses filters for both will certainly be using narrow enough bandpasses that the two are distinctly separated, and can be mapped to different colors in post processing in order for the two atomic species to be clearly distinguished.

Yes, I'm not questioning the usefulness of these two bandpasses in narrowband images. I'm just saying that optically, these two shades of red are virtually the same hue - and the same RGB values and the same hexadecimal letters and numbers are used to describe them: R=255, G=0, B=0, and hex: #FF0000.

https://academo.org/demos/wavelength-to ... ationship/

Ann

[Chris Peterson]

Okay. I'll provide the info that Art didn't.

The source of the picture is this page. It is an ESO image, and the photographer is Sergey Stepanenko. The filters used for the image were SII and H-alpha. Optically, these two filters actually detect the same shade of red, but H-alpha represents a higher degree of ionization than SII.

Singly ionized sulfur (S II) produces a doublet, at 671.6 and 673.1 nm. H-alpha produces a line at 656.28 nm. They are close, and many narrowband filters are wide enough to pass both. But they are definitely different shades of red, and an imager who uses filters for both will certainly be using narrow enough bandpasses that the two are distinctly separated, and can be mapped to different colors in post processing in order for the two atomic species to be clearly distinguished.

Yes, I'm not questioning the usefulness of these two bandpasses in narrowband images. I'm just saying that optically, these two shades of red are virtually the same hue - and the same RGB values and the same hexadecimal letters and numbers are used to describe them: R=255, G=0, B=0, and hex: #FF0000.

https://academo.org/demos/wavelength-to ... ationship/

Ann

For wavelengths longer than about 650 nm, only our red receptor is firing, so all reds look the same hue. The only way you could distinguish two equally bright sources, on Ha and the other S II is by brightness- the latter would appear dimmer.