APOD: The Cygnus Wall of Star Formation (2016 Oct 11)

[APOD Robot]

The Cygnus Wall of Star Formation

Explanation: Sometimes, stars form in walls -- bright walls of interstellar gas. In this vivid skyscape, stars are forming in the W-shaped ridge of emission known as the Cygnus Wall. Part of a larger emission nebula with a distinctive outline popularly called The North America Nebula, the cosmic ridge spans about 20 light-years. Constructed using narrowband data to highlight the telltale reddish glow from ionized hydrogen atoms recombining with electrons, the image mosaic follows an ionization front with fine details of dark, dusty forms in silhouette. Sculpted by energetic radiation from the region's young, hot, massive stars, the dark shapes inhabiting the view are clouds of cool gas and dust with stars likely forming within. The North America Nebula itself, NGC 7000, is about 1,500 light-years away.

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[Ann]

Congratulations, Sara! I don't remember the last time a woman's image was made the Astronomy Picture of the Day.

Yours is very well-deserved. All the dusty features in and near the Cygnus Wall are very intriguing.

Ann

[starsurfer]

Congratulations, Sara! I don't remember the last time a woman's image was made the Astronomy Picture of the Day.

Yours is very well-deserved. All the dusty features in and near the Cygnus Wall are very intriguing.

Ann

I concur! Female astrophotographers are very rare.

[Muppet]

I think I see a fierce battle between hand puppets in the lower left corner.

[MarkBour]

How opaque are the clouds? I would guess that they are more or less completely opaque. When I see a dark region with stars in it, my mind wants to assume the stars are shining through a mostly-clear darkness. For this picture, though, I'm guessing that all of the stars one sees in the otherwise dark cloudy regions are in front of the clouds of dust. Of course, someone, at some point, would need to establish that, but I assume that's been long since done. The black region at the upper left of the image is distinct from the brown region at the lower right, so the answers may be different for the two regions, maybe not. Is this correct for this image -- all of the stars in the dark regions are between us and an opaque cloud?

[ta152h0]

is this wall really of very tenuous density ? If you were able to maintain your human form and fly thru there, you would feel nothing, maybe.

[ta152h0]

never seen a woman's image on APOD ? Remember the Marylin Monroe nebula ?

[Fred the Cat]

I always wonder, "What would that nebula look like if you could see it in 3D?"

[MarkBour]

I always wonder, "What would that nebula look like if you could see it in 3D?"

That is fantastic. Actually, if they have all that data, they could make it interactive like the recent APOD image of C67P. I'd like that even better.

[Chris Peterson]

I always wonder, "What would that nebula look like if you could see it in 3D?" 8-)

That is fantastic. Actually, if they have all that data, they could make it interactive like the recent APOD image of C67P. I'd like that even better.

Don't overlook that there is little actual data here. The 3D reconstruction is largely speculative, and doesn't represent the actual 3D structure. Best to think of it as representative, to give a subjective sense of the 3D structure of such nebulas, not an objective representation of this particular nebula.

[Chris Peterson]

How opaque are the clouds? I would guess that they are more or less completely opaque.

You need to define what you mean by "opaque" when asking that kind of question. The densest parts of the clouds are still a hard vacuum. Much more tenuous than Earth's atmosphere, for instance. And our atmosphere is more opaque by orders of magnitude than this nebula.

[neufer]

How opaque are the clouds? I would guess that they are more or less completely opaque.

You need to define what you mean by "opaque" when asking that kind of question. The densest parts of the clouds are still a hard vacuum. Much more tenuous than Earth's atmosphere, for instance. And our atmosphere is more opaque by orders of magnitude than this nebula.

[b][color=#0000FF][size=200]The Horsehead Nebula[/size][/color][/b]

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<<A dark nebula or absorption nebula is a type of interstellar cloud that is so dense it obscures the light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. In the inner outer molecular regions of dark nebulae, important events take place, such as the formation of stars and masers.

Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen carbon monoxide and nitrogen, which effectively block the passage of light at visible wavelengths. Also present are molecular hydrogen, atomic helium, C¹⁸O (CO with oxygen as the ¹⁸O isotope), CS, NH₃ (ammonia), H₂CO (formaldehyde), c-C₃H₂ (cyclopropenylidene) and a molecular ion N₂H⁺ (diazenylium), all of which are relatively transparent. These clouds are the spawning grounds of stars and planets, and understanding their development is essential to understanding star formation.

The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The largest dark nebulae are visible to the naked eye, appearing as dark patches against the brighter background of the Milky Way like the Coalsack Nebula and the Great rift. These naked-eye objects are sometimes known as dark cloud constellations and take on a variety of names.>>

[dlw]

Beautiful! It bring to mind a very well known image of another form of "creation".

Michelangelo - Creation of Adam, Sistine Chapel

[MarkBour]

How opaque are the clouds? I would guess that they are more or less completely opaque.

You need to define what you mean by "opaque" when asking that kind of question. The densest parts of the clouds are still a hard vacuum. Much more tenuous than Earth's atmosphere, for instance. And our atmosphere is more opaque by orders of magnitude than this nebula.

I see the vagueness possible in this question, but I'm using opaque in the basic sense "not able to be seen through" ... and I mean the cloud as a whole, not some portion of it. I tried to clarify it when I said: "I'm guessing that all of the stars one sees in the otherwise dark cloudy regions are in front of the clouds of dust."

I'm supposing that clever astronomers have found some way to decide the distance and rough extent of the clouds, and I'm betting they can do an even better job of telling the distance to many of the stars in the image. If we can see plenty of stars that are beyond the cloud, then I would not call it opaque in the sense I am asking. If we are not seeing any starlight that is coming to us through the cloud, then there is some evidence that it is sufficiently opaque to hide stars from us.