APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

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APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by APOD Robot » Wed Dec 14, 2016 5:07 am

Image The Lagoon Nebula in High Definition

Explanation: Stars are battling gas and dust in the Lagoon Nebula but the photographers are winning. Also known as M8, this photogenic nebula is visible even without binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M8 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. The light from M8 we see today left about 5,000 years ago. Light takes about 50 years to cross this section of M8. Data used to compose this image was taken with the wide-field camera OmegaCam of the ESO's VLT Survey Telescope (VST).

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Wed Dec 14, 2016 7:06 am

This is a lovely image!
Image
The slave ship.
Painting: William Turner.
The loveliness of the colors of today's APOD reminds me of a William Turner painting, except that Turner excelled in yellow and orange hues (and some blues) while today's APOD is a study in pink. But the APOD version of the Lagoon Nebula also looks like candy cotton in heaven, so I can't resist posting the picture at right!



In the APOD, note the fantastically rich palette of rosy hues in the nebula itself. Note the dusty details, the pitch-dark Bok globules, the illuminated ridges. Note the myriads of small yellow stars scattered over most of the nebula, which in many cases have been born at the same time as the few brilliant blue stars that power the nebula itself. But some of the yellow stars are foreground or background objects.

Note the bluish tint of the dust lanes that encompass the Lagoon at top and bottom. This faint blue light is undoubtedly reflection nebulosity, similar to but much fainter and less extended than the blue reflection component of the Trifid Nebula, seen here in an image by Scott Rosen.
Image
Photo: Robert Harding
I have a small quibble about the color of the star 9 Sagittarius, situated immediately to the east (left) of the bright central Hourglass nebula. 9 Sagittarius is a blue star, not just intrinsically blue (because it is an O star) but also relatively blue in appearance, bluer than HD 165052, the blue star at 9 o'clock in the APOD.

I would guess that the non-blue appearance of 9 Sagittarius in the APOD is due to the brightness of the vicinity of this star. There must be a lot of Ha and OIII around 9 Sgr, and it is probably hard to color-balance a star correctly if it is surrounded by so much bright nebula light.

Also I would think the brightness of this part of the Lagoon Nebula has been purposely reduced somewhat, to make its central details more apparent and to make other, darker parts of the nebula sufficiently bright to convey a lot of information. This fiddling with the brightness of the nebula could probably play havoc with the color-balancing of the brightest part of the Lagoon.

Nevertheless, I love today's APOD!

Ann
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by neufer » Wed Dec 14, 2016 2:17 pm

Ann wrote:
This is a lovely image!

I love today's APOD!

Ann
Whatever happened to our "better dead than red" Ann :?:
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Wed Dec 14, 2016 2:49 pm

neufer wrote:
Ann wrote:
This is a lovely image!

I love today's APOD!

Ann
Whatever happened to our "better dead than red" Ann :?:
Better dead than red, perhaps.

But not better dead than PINK!!!

Ann
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Astrovideobear » Wed Dec 14, 2016 2:54 pm

What is the thing that looks like a big eyeball, right side of the image, just above center?

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by rstevenson » Wed Dec 14, 2016 3:06 pm

Astrovideobear wrote:What is the thing that looks like a big eyeball, right side of the image, just above center?
A big eyeball.

Rob

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Wed Dec 14, 2016 3:10 pm

Astrovideobear wrote:What is the thing that looks like a big eyeball, right side of the image, just above center?
It's a star. The rings around it and to one side of it are caused by reflections in the optics.

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by neufer » Wed Dec 14, 2016 3:25 pm

rstevenson wrote:
Astrovideobear wrote:
What is the thing that looks like a big eyeball, right side of the image, just above center?
A big eyeball.

Rob
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by MarkBour » Wed Dec 14, 2016 5:39 pm

Ann, thanks for the additional info ... a helpful tour.
Capture.JPG
What causes the more orange/brown coloration in the clouds at the right of the image?
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by neufer » Wed Dec 14, 2016 11:09 pm


MarkBour wrote:
What causes the more orange/brown coloration in the clouds at the right of the image?
at the right AND the bottom of the image.

It's not the Lagoon Nebula...
possibly a mixed-sand & gravel
Milky Way coastline :?:
https://en.wikipedia.org/wiki/Lagoon wrote:
<<A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons have also been identified as occurring on mixed-sand and gravel coastlines.>>
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Thu Dec 15, 2016 12:08 am

MarkBour wrote:Ann, thanks for the additional info ... a helpful tour.
Capture.JPG
What causes the more orange/brown coloration in the clouds at the right of the image?
Basically, interstellar dust is "brown" in itself.
Dust cloud. Photo:
Michael Skrutskie of University of Virginia
Take a look at the picture of an interstellar dust cloud at left. As you can see, the dust cloud is blocking more and more of the light from the stars behind it. But interestingly, the starlight that shines through the dust is getting more and more red. In this picture, the whitish-blue starlight is getting first yellow, then orange, then reddish, then dark brown.

What happens is that the dust cloud blocks the shortwave light first - ultraviolet, violet, blue, then it blocks the green light, then yellow, then orange, then red.

The reason for this is that the size of the interstellar dust particles themselves are typically about the same size - 450 nm or so - as the wavelength of blue light. This means that shortwave photons are preferentially blocked by dust particles, whereas longwave photons more easily get through. Check out this page for a fine illustration of how this happens.
Image
So when interstellar dust is in front of a light source, it reddens the light from that source. However, when interstellar dust is right behind a light source, it scatters light our way. And while dust in front of a light source "steals" the blue photons from that light source, dust right behind a light source preferentially scatters blue light right back at us. Why are the Pleiades blue? Because the bright stars are blue in themselves, and the dust right behind them scatters some of their blue light right back at us.
Image
Antares. Photo via Dick Loke.
The bright stars of the Pleiades are blue in themselves, but other light sources aren't blue at all. Why is the dust near Antares yellow? It is because dust behind Antares is scattering yellow light back at us. The Antares nebula is a yellow reflection nebula.
M63. Photo: HST/Renaud Houdinet.
If you bear in mind that dust that is in front of us will redden and darken a light source, while dust that is behind it will make it brighter (and often, but not always, bluer), then you can tell by looking at a highly (or moderately) inclined galaxy which side of it is closer to us. Take a look at the picture of M63 at right. The dust lanes below the bright center of the galaxy look particularly dark. That means that they are in front of us, blocking light from the center. Above the center, however, the dust looks "pale". This dust is behind the bright center and scatters light our way.

Let's return to the question of the brown dust of the Lagoon Nebula. The brown dust is blocking some light behind it, and it isn't scattering any blue light our way.
The Trifid Nebula. Photo: ESO.






Check out this ESO image of the Trifid Nebula. At top, the Trifid is blue from reflection nebulosity. Blue light is scattered our way. But look at the particularly dark black smudge of dust at right. This dust appears to flow outwards, like smoke from a chimney. Some of this dust is in front of the scattered blue light, and look what happens. The reflection nebula on the right side of the Trifid Nebula is wan, faded and gray. In some pictures it looks greenish. This is an example of blue light first being scattered our way and then partly blocked by dust in front of it.

Hope that clarified the question of reflection nebulas and dust!

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by rstevenson » Thu Dec 15, 2016 1:09 am

That was an excellent explanation, Ann. It clarified things I thought I knew, making them much more colourful and therefore more memorable. You must be a teacher! ;-)

Rob

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Thu Dec 15, 2016 1:25 am

rstevenson wrote:That was an excellent explanation, Ann. It clarified things I thought I knew, making them much more colourful and therefore more memorable. You must be a teacher! ;-)

Rob
Well... I am. :wink:

And thanks for the praise! :D

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by neufer » Thu Dec 15, 2016 1:34 pm

Ann wrote:
rstevenson wrote:
That was an excellent explanation, Ann. It clarified things I thought I knew, making them much more colourful and therefore more memorable. You must be a teacher! ;-)
  • Well... I am. :wink:
Teacher neglected to mention that the orange Milky Way shown is false color infrared
  • (5.8 micron radiation from Spitzer's Infrared Array Camera ?).
In the visible space dust shows up locally as scattered blue light or as obscured dark red light.
(Only in :cowboy: movies does dust show up as orange from one side of the screen to the other.)
http://www.spitzer.caltech.edu/images/1541-ssc2006-02a1-Spitzer-View-of-the-Center-of-the-Milky-Way wrote: <<This dazzling infrared image from NASA's Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. In visible-light pictures, this region cannot be seen at all because dust lying between Earth and the galactic center blocks our view.

In this false-color picture, old and cool stars are blue, while dust features lit up by blazing hot, massive stars are shown in a reddish hue. Both bright and dark filamentary clouds can be seen, many of which harbor stellar nurseries. The plane of the Milky Way's flat disk is apparent as the main, horizontal band of clouds. The brightest white spot in the middle is the very center of the galaxy, which also marks the site of a supermassive black hole.

The region pictured here is immense, with a horizontal span of 890 light-years and a vertical span of 640 light-years. Earth is located 26,000 light-years away, out in one of the Milky Way's spiral arms. Though most of the objects seen in this image are located at the galactic center, the features above and below the galactic plane tend to lie closer to Earth.>>
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by edibleplantguy » Fri Dec 16, 2016 12:28 pm

For me the three large optical defects around the three brightest stars in the image (noted below as caused by reflections withing the optical system) described a looking like an 'eyeball,' bring the image below APOD standards.

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by neufer » Fri Dec 16, 2016 1:17 pm

edibleplantguy wrote:
For me the three large optical defects around the three brightest stars in the image (noted below as caused by reflections withing the optical system) described a looking like an 'eyeball,' bring the image below APOD standards.
  • APOD standards :?:
It is an appealing picture that never claims to be anything that it's not.
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Fri Dec 16, 2016 2:08 pm

neufer wrote:
Ann wrote:
rstevenson wrote:
That was an excellent explanation, Ann. It clarified things I thought I knew, making them much more colourful and therefore more memorable. You must be a teacher! ;-)
  • Well... I am. :wink:
Teacher neglected to mention that the orange Milky Way shown is false color infrared
  • (5.8 micron radiation from Spitzer's Infrared Array Camera ?).
In the visible space dust shows up locally as scattered blue light or as obscured dark red light.
(Only in :cowboy: movies does dust show up as orange from one side of the screen to the other.)
Ummm... mea culpa?

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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Ann » Sun Dec 18, 2016 5:29 am

MarkBour wrote:Ann, thanks for the additional info ... a helpful tour.
Capture.JPG
What causes the more orange/brown coloration in the clouds at the right of the image?
Mark, I need to rephrase my answer to you. What I told you about the effects of light-blocking and light-scattering dust was correct, but it wasn't a really good answer to your question. You wanted to know why the rightmost part of the Lagoon Nebula looks so orange-brown, and I told you it was just because of the dust, but that wasn't a very good answer. If it had been "just" dust blocking the light from behind, it would have been darker, not as lightly toffee-colored as it is in the APOD.

The reason why it looks the way it looks is likely because this part of the nebula is a mixture of a faint light-emitting red Ha nebula and a brownish dust nebula blocking light from behind.
The Lagoon Nebula. Photo: Roberto Colombari.
Often you can understand a picture better by comparing it with another picture of the same motif. At left you can see another portrait of the Lagoon Nebula by Roberto Colombari, and this other portrait of the Lagoon by the same author can shed light on the new APOD.

In the portrait of the Lagoon at left, you can see "broken fragments" of the nebula at right. These "fragments" are not quite the same color as most of the rest of the nebula. They are less pink and more reddish, particularly the outermost of them. They are also fainter.

As I said, I think the toffee-colored parts of the nebula in the APOD are a mixture of emission nebulosity and dust reddening. They emit relatively low levels of ionized hydrogen, because they are relatively far away from the really hot stars of the Lagoon. The brilliant star on the right side of the Lagoon Nebula is 7 Sagittarius, an F-type giant, which is absolutely not hot enough to ionize an emission nebula.

The red light we can see in the outermost right parts of the nebula in the picture here, and to some extent also in the APOD, would be low levels of Ha, ionized by stars far to the left of it, and quite possibly also red SII emission.

The red Ha (and SII) adds brightness to the filaments at right. But these filaments also contain dust. The dust blocks light from behind, making it darker and browner.
Widefield image of the Lagoon and Trifid nebulas.
Photo: Takayuki Yoshida.
Let's not forget that there is an incredibly rich and quite yellow Milky Way background behind the Lagoon. The background stars we see belong to the bright yellow bulge of our galaxy. This large (533 Kb) image gives you a good idea of the dusty field that the Lagoon nebula is a part of, and the yellow Milky Way bulge seen behind it.

So some faint emission nebulosity lights these filaments up, while the dust in them blocks some of the comparatively bright light from the rich background star field. The net effect is the brownish color of the filaments at right in the Lagoon.

To the left of the Lagoon you can see this effect even more clearly. Faint red emission lights it up, and dust darkens the background and makes it more orange-brown.

And that is why the rightmost parts of the Lagoon Nebula look so toffee-colored in the APOD.

Ann
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Re: APOD: The Lagoon Nebula in High Definition (2016 Dec 14)

Post by Chris Peterson » Sun Dec 18, 2016 3:30 pm

edibleplantguy wrote:For me the three large optical defects around the three brightest stars in the image (noted below as caused by reflections withing the optical system) described a looking like an 'eyeball,' bring the image below APOD standards.
You should check out the optical and sensor defects found on the science images of the Hubble and virtually all professional telescopic imagers!
Chris

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