APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Comments and questions about the APOD on the main view screen.
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APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by APOD Robot » Thu Sep 29, 2011 4:06 am

Image Cocoon Nebula Wide Field

Explanation: In this crowded starfield spanning some 3 degrees within the high flying constellation Cygnus, the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a long trail of obscuring interstellar dust clouds. Cataloged as IC 5146, the nebula is nearly 15 light-years wide, located some 4,000 light years away. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by the young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. But the long dusty filaments that appear dark in this visible light image are themselves hiding stars in the process of formation, seen at infrared wavelengths.

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Ann
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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by Ann » Thu Sep 29, 2011 4:26 am

It's good to see Tony Hallas back here! He's a very good astrophotographer, but I haven't seen much of him lately. It's nice to have him here! :D

The Cocoon Nebula, IC 5146, is interesting. The simple fact that it looks like a small celestial rose attached to a long, slightly broken and multiple dark stem which stretches away in only one direction, is interesting. To me, this overall shape of the Cocoon Nebula seems to be a prime example of how interstellar molecular clouds can form long, farily narrow structures, where star formation may very well start at one end of the elongated cloud. Another thing that is very noteworthy to me is that the Cocoon apparently contains just a single massive star (which is responsible for ionizing the hydrogen gas in the nebula and making it glow red), although the Cocoon is also busy producing several low-mass hatchlings.

As for the nebula itself, note how the ultraviolet photons, which are responsible for creating the ionized red hydrogen glow, drop off in intensity at a distance from the central star where there are still enough blue photons to be scattered by dust and create a blue reflection nebula. The blue reflection nebula is therefore seen farther away from the hot bright star than the red emission nebula.

Today's APOD is a beautiful image, and I love the crowded star field. Cygnus is a part of the sky where there are many young and intermediate-aged stars, which makes it seem quite probable that there should be a large number of blue stars in the crowded background field.

Ann
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Joe Stieber
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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by Joe Stieber » Thu Sep 29, 2011 4:54 am

The text fails to specificlly identify Barnard 168, the dark nebula that's so prominent on the right-hand side of the picture. B168 is one of the most accessible dark nebulae, and unlike the Cocoon Nebula, it can easily be seen with binoculars from a reasonably dark site. My 16x70s provide a splendid view from the New Jersey Pinelands.

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by cketter » Thu Sep 29, 2011 5:42 am

I love this exposure; it really contrasts the dark nebula against the rest of the image.
I wonder if the dark nebula has a depth as long as it's apparent width, does anyone know the answer to this?
Also, why do all the stars appear blue and orange in this visible light image? does this have something to do with the settings on the imaging sensor used?

Chris

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by paulobao » Thu Sep 29, 2011 7:28 am

Hello,

well said Ann and Joe (about the astronomic festures in this image). This is really a great object and not that easy to process right!

Chris, you are completely right....this image have so many blue (specially those blue halos that I'm wondering...(?)).
Here in portugal is 8:20 am now and I need to put my childs in the school, but I had 10 minute to make a quick mod. to this image. Let me know if you like it more like this : http://img685.imageshack.us/img685/746/ ... odifie.jpg. (with time much more could be done....I like to process the images as all the precious pixels counts...but I have no time for now!)
Of course all rights are for Tony and I hope he do not mind I put the modified image here!

Regards,
paulo

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by cketter » Thu Sep 29, 2011 9:11 am

paulobao wrote: Let me know if you like it more like this :
Yes, I do like this version more. I put both in alternate tabs and flipped back and forth...very noticable difference.

I especially like Ann's description of a rose and dark stem.

I must retire now, it's 11pm here...so good night... :? ...or good morning?

Chris

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by Indigo_Sunrise » Thu Sep 29, 2011 10:37 am

Joe Stieber wrote:The text fails to specificlly identify Barnard 168, the dark nebula that's so prominent on the right-hand side of the picture. B168 is one of the most accessible dark nebulae, and unlike the Cocoon Nebula, it can easily be seen with binoculars from a reasonably dark site. My 16x70s provide a splendid view from the New Jersey Pinelands.
Joe,
If you click the link for IC 5146, and scroll about two thirds down (second paragraph from the end), Barnard 168 is touched on - albeit briefly - there.



Very nice image!
8-)
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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by orin stepanek » Thu Sep 29, 2011 11:50 am

It is amazing how many stars are in this field and yet around the new star they are spread out. 8-)
Orin

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Ms. Snooty

Post by neufer » Thu Sep 29, 2011 3:12 pm

http://en.wikipedia.org/wiki/Max_Rebo_Band#Sy_Snootles wrote:
Image
<<Sy Snootles is a robust female Pa'lowick who is the lead vocalist and original member of the Max Rebo band. She is angered at Max's acceptance of Jabba's contract, and after attempts to rework the deal prove futile, Sy resorts to secretly spying for over a dozen of Jabba's enemies to earn credits, but then works as a double agent by giving them false information provided by Bib Fortuna. She was also not above getting her hands dirty when she killed Ziro the Hutt to obtain for Jabba a book containing dirt on the other Hutt leaders.

She teams up with Max as the Max Rebo Duo following Jabba's death and Droopy's departure from the band. Following a brief gig for Lady Valarian, Sy dissolves her relationship with Max and begins her solo career, but her subsequent recordings sell poorly and she is relegated to touring Outer Rim dives under different stage names. Also in later life Snootles became a spice addict, whilst trying to reach the fame she craved but never achieved.

During production, Sy Snootles' nickname was "Ms. Snooty."
In the original version of the film, the character was a marionette-like puppet operated by puppeteers Mike Quinn and Tim Rose; Quinn was stationed on scaffolding and controlled her upper body, while Rose moved her legs from beneath the set. The character's oversized ruby lips were suggested by George Lucas, who referred to them as "Mick Jagger lips."

Sy was voiced in the original version of Jedi by Lucasfilm sound engineer Annie Arbogast, who also wrote the Huttese-language lyrics to "Lapti Nek." The track was recorded at Lucasfilm's Sprocket Systems (currently Skywalker Sound), and was even the recipient of a 1983 Apex Award. For close-up shots, Sy's mouth was articulated using a nearly-invisible wire connected to a microphone stand. The puppet was replaced with a computer-generated image for the Special Edition rerelease.>>
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Joe Stieber
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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by Joe Stieber » Thu Sep 29, 2011 3:26 pm

Indigo_Sunrise wrote:
Joe Stieber wrote:The text fails to specificlly identify Barnard 168...
Joe,
If you click the link for IC 5146, and scroll about two thirds down (second paragraph from the end), Barnard 168 is touched on - albeit briefly - there.
Yes, I had to scroll down a bit to find the Barnard 168 reference. Since both Hallas’ APOD and Davis’ image at Universe Today (the IC5146 link) were nicely framed to intentionally include B168, I just think it might have deserved more prominent mention. I’ve seen a number of amateur images where the Cocoon is centered in a relatively wide field and B168 is simply chopped off at the edge of the frame – that’s irksome!

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by Ann » Thu Sep 29, 2011 5:42 pm

cketter wrote:I love this exposure; it really contrasts the dark nebula against the rest of the image.
I wonder if the dark nebula has a depth as long as it's apparent width, does anyone know the answer to this?
Also, why do all the stars appear blue and orange in this visible light image? does this have something to do with the settings on the imaging sensor used?Chris
I doubt that the nebula is as wide as it is long. Note that much of the dark nebula is half "transparent", suggesting it isn't very wide. Besides, if such "sheet-shaped" nebulae were common in the Milky Way, a number of them ought to have been photographed by now.

Why do so many of the background stars appear blue and orange? Part of the answer is that photographer Tony Hallas, for aesthetic reasons, has chosen a fairly high level of color saturation for his image. But another and more interesting answer is that the stars probably really are blue and orange, and that is because many of the stars are young. Here is how it works.

When a young cluster is born, its brightest members are blue. These are typically of spectral classes A and B. Take a look at this great image by Enzo Santin of the very young starforming region NGC 7129. The brightest stars hatching out of this molecular cloud are blue stars of spectral classes A and B. The hottest (and therefore certainly brightest) of these very young stars are of spectral class B3, according to http://iopscience.iop.org/0067-0049/154 ... .text.html, a paper discussing the infrared properties of NGC 7129:
The primary sources of photoionization, the B3 stars BD +65°1637 and BD +65°1638, are not detected directly [in the infrared], but extended halos of warm dust are seen at their positions.
However, the authors of this paper have found 39 likely young proto-stars which have not yet reached the main sequence. Many of them are very faint.

Take a look at Enzo Santin's NGC 7129 image again. Three bright sources can be seen which are deeply embedded in dust and very orange. Otherwise, the brightest stars in the cluster appear to be blue or bluish.

These stars are less than a million years old, according to http://en.wikipedia.org/wiki/NGC_7129. As the cluster ages, most or all of the dust will be blown away. The initial effect of this will likely be to make the overall light of the cluster bluer. You can see for yourself that much of the reddening of this cluster is clearly caused by dust.

However, after perhaps a hundred million years or so, the brightest blue stars, those of spectral class B3, will have used up the hydrogen in their cores. When this happens they will expand and turn into red giants, probably red giants that are very large, bright and reddish as giants go. Perhaps they will turn into M-class giants like, say, Mirach, Beta Andromedae, a bright M0III giant about 450 times as bright as the Sun in visual light. But the former blue class B3 stars will not stay in their M0III stage for long: after less than an additional one hundred million years they will shed their outer atmospheres, turning into small hot compact stars surrounded by planetary nebulae.

Now the brightest stars of NGC 7129 will be gone, or at least they will have become very faint compared with what they used to be. By now, however, other formerly blue stars of NGC will have turned into red giants, probably of spectral class K. These formerly blue stars were never as blue or as bright as the stars of class B3, and the red giants they turn into will similarly not be as bright or as red as the red giants that the B3 stars turned into. Nevertheless, these "lesser blue stars" will become red giants too, perhaps similar to Aldebaran, the bright K-type star that seems to be superimposed on the Hyades cluster.

So first the class B3 stars will turn into red giants. Then the stars of late class B will do the same. Then the stars of early class A like Vega and Sirius will become red giants like Arcturus and Dubhe. Then the stars of late class A, like Altair, will follow suit. Then the stars of class F, like Procyon. After perhaps ten billion years, even the stars of early class G like the Sun will turn into red giants.

So the youngest, brightest stars are blue. Many of the not quite so bright young stars are blue, too. The not so bright stars stay blue longer than the very hot ones. But eventually, they all turn into orange stars, the red giants.

What do we see in today's APOD? We see a star field dominated by blue and orange stars. My guess is that a majority of the blue stars are main sequence class A (or early F) stars, whereas a majority of the orange stars are orange-colored red giants of spectral class K. The blue stars are likely all younger than, say, a billion years old (and most of them are probably younger than 500 million years). That's fairly young. Some of the orange stars are probably fairly young, too, while others may be older than the Sun.

What about the stars that are like the Sun? Main sequence stars of spectral class G? We likely see few of them in the field of today's APOD. Why is that? It's because they are so much fainter than the main sequence A-type stars and the K-type red giants. That doesn't mean that our Sun is faint as stars go, rather the opposite. In fact, we have reason to believe that our Sun belongs to the top 5% echelon in the brightness competition league of our galaxy! In other words, 95% of the stars of the Milky Way are likely fainter than the Sun! But these stars are so faint that we are not likely to see more than, at best, two or three in a rich background field like the one in today's APOD.

After all, what stars dominate the skies of the Earth? Of the 25 visually brightest stars in the sky, six belong to spectral class A and seven to spectral class B. Three belong to spectral class K and three to spectral class M. The K and M stars are all either giants or supergiants. All are intrinsically brighter than the Sun. All of them, with the exception of Alpha Centauri, are likely to be younger than the Sun. (Though it has to be said that it is not so easy to determine the age of K-type giants.)

But if we look at the most nearby stars, 18 of the 29 nearest stars are tiny red main sequence stars of spectral class M. They are all so faint that it is impossible to see even a single one of them with the naked eye, even though they are so comparatively nearby.

In the same way as the Earth's sky is dominated by intrinsically bright young blue or orange stars, in the same way a distant starry background like the one in today's APOD is likely to be dominated by intrinsically relatively bright blue and orange stars.

So to summarize: The crowded background in today's APOD looks the way it does because there is a large fraction of young bright stars in it.

Ann
Last edited by Ann on Fri Sep 30, 2011 8:25 am, edited 7 times in total.
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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by starstruck » Thu Sep 29, 2011 7:10 pm

Thanks Ann for the insights; there's much more to this APOD than is at first apparent to my untrained eyes.
I have to admit, when I first saw this picture I simply thought, "Mon Dieu!, c'est plein d'étoiles!"

Had we but world enough, and time . . .

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by islander2 » Fri Sep 30, 2011 5:33 am

Ann, maybe "sheet nebulae" are so rare is because the picture shows two dimensions only. It seems hard to believe that a star would blow off its matter in only two dimensions. { I am always thrilled by your excellent posts.} :D Thanx. :)

Thanx. :D :D

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Re: APOD: Cocoon Nebula Wide Field (2011 Sep 29)

Post by paulobao » Fri Sep 30, 2011 8:13 am

One thing is blue stars (that you may see in M13 for example) another thing is blue halos (Halas :-)). The same for the orange/red ones!!!!
This picture deserved a reprocess to diminish/remove both.
And at the upper right corner the stars are elongated too!

And yes, there are lots of stars (Why should they not be there?... afterall the object is very near the galactic plane!)

Regards,
paulo