APOD: Horsehead and Orion Nebulas (2013 Oct 29)

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APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby APOD Robot » Tue Oct 29, 2013 4:11 am

Image Horsehead and Orion Nebulas

Explanation: The dark Horsehead Nebula and the glowing Orion Nebula are contrasting cosmic vistas. Adrift 1,500 light-years away in one of the night sky's most recognizable constellations, they appear in opposite corners of the above stunning mosaic. The familiar Horsehead nebula appears as a dark cloud, a small silhouette notched against the long red glow at the lower left. Alnitak is the easternmost star in Orion's belt and is seen as the brightest star to the left of the Horsehead. Below Alnitak is the Flame Nebula, with clouds of bright emission and dramatic dark dust lanes. The magnificent emission region, the Orion Nebula (aka M42), lies at the upper right. Immediately to its left is a prominent reflection nebula sometimes called the Running Man. Pervasive tendrils of glowing hydrogen gas are easily traced throughout the region.

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby owlice » Tue Oct 29, 2013 4:11 am

Stunning mosaic, indeed! This is really lovely.
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Beyond » Tue Oct 29, 2013 4:39 am

It's such a BIG vista, the Horsehead is so small :!:
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ann » Tue Oct 29, 2013 4:40 am

This is a great mosaic! :D

To me as a color commentator, the colors are of course particularly interesting here. Note how Sigma Orionis, the blue star seen just "above" the Horsehead Nebula, appears to have blown a "hole" around itself in the bright red-glowing ionized hydrogen that surrounds it. This is indeed what hot massive stars do: how else would the Rosette Nebula have gotten its shape?

And all those "brownish" tendrils of gas filling so much of the scene get their color from hydrogen at low levels of ionization. Almost the entire skyscape here is filled with glowing hydrogen.

What a great picture!

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Chris Peterson » Tue Oct 29, 2013 5:08 am

Ann wrote:And all those "brownish" tendrils of gas filling so much of the scene get their color from hydrogen at low levels of ionization. Almost the entire skyscape here is filled with glowing hydrogen.

It seems to me there are at least three possibilities, and nothing obvious in this image to sort them out. The brown areas could be hydrogen regions only weakly ionized. They could be highly ionized, but low density, and therefore relatively low intensity. They could be dust tendrils, just reflecting light from surrounding hydrogen regions.
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Boomer12k » Tue Oct 29, 2013 7:41 am

Two of my favorite places that whole complex is awesome in the wide angle photos....

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ann » Tue Oct 29, 2013 10:56 am

Chris Peterson wrote:
Ann wrote:And all those "brownish" tendrils of gas filling so much of the scene get their color from hydrogen at low levels of ionization. Almost the entire skyscape here is filled with glowing hydrogen.

It seems to me there are at least three possibilities, and nothing obvious in this image to sort them out. The brown areas could be hydrogen regions only weakly ionized. They could be highly ionized, but low density, and therefore relatively low intensity. They could be dust tendrils, just reflecting light from surrounding hydrogen regions.


Obviously I can't really argue with you, Chris. Nevertheless, I would like to explain why I thought of low-level ionization here. I remember when this picture first appeared, from which astronomers concluded that there are low levels of ionized hydrogen almost everywhere in our galaxy.

As for today's APOD, it seemed to me that the area between the Horsehead Nebula and M42 is the perfect place to look for gas at relatively low levels of ionization. There are many hot bright stars in the region, whose stray ultraviolet photons could ionize some of the hydrogen atoms some distance away from the obvious emission nebulae.

If you look at this picture of Orion by Rogelio Bernal Andreo, you can see that the region between the Horsehead and M42 looks reddish brown. I think it is more likely that we are looking at undulating gas at low levels of ionization than that we are seeing a huge rippling sheet of dust. Compare the appearance of the area between the Horsehead and M42 with T.V. Davis image of the Iris Nebula region. Note that HD 200775, the bright blue star inside the Iris Nebula itself, is the only star in the vicinity that is hot enough to do an appreciable amount of hydrogen ionization in the first place - and yet, the nebula surrounding this star is primarily a reflection nebula, with only some small hints of pink emission nebulosity near the star itself. It is very hard to believe that HD 200775 packs an ultraviolet punch that can "reach out" to hydrogen far away from itself and kick such distant electrons into a "higher orbit".

But look at the dark dust near the Iris Nebula! The dust is very clumpy, and some of it is very dark. Compare it with the undulating structures between the Horsehead and M42. Even though Roberto Colombari & Federico Pelliccia's mosaic isn't strikingly Ha-bright, it is clear that the color of the tendrils is different from the color of the clumps of dust near the Iris Nebula. Also, there are no very dark or strikingly clumpy features among the undulating structures in Orion. That is why I don't believe that the structures that we see are primarily clumps or strings of dust.

In any case, this is a picture of Orion in Ha light only. The area between the Horsehead and M42 clearly shows up is Ha.

As for the suggestion that the tendrils that we see could just reflect the color of the bright red emission nebulae in the area, I don't believe that that is even remotely possible. Bear in mind that dust typically reflects blue light better than red light, and with all the bright blue stars in Orion, there is no doubt that there is more blue than red light available here for the dust to reflect.

But what about the dust structures near the Iris Nebula? They are clearly reflecting some kind of light, but not red Ha light and certainly not blue light from HD 200775. So what light do they reflect? I believe they reflect the combined light of the Milky Way and the various photons that are travelling this way and that inside our galaxy. Our own galaxy is likely somewhat "red" in color, with its large bulge and thick central dust lane. And the dust grains in themselves are also likely somewhat reddish in color, which in combination with the yellowish light from the Milky Way would explain the brown color of the dust clouds.

So in my opinion, the faintly wine-colored tendrils that we see in today's APOD are not dust structures. But isn't it possible that they are very low density gas tendrils that are highly ionized, although there is very little there to ionize? Yes, I suppose that is possible, Chris.

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby starsurfer » Tue Oct 29, 2013 12:05 pm

Ann wrote:This is a great mosaic! :D

To me as a color commentator, the colors are of course particularly interesting here. Note how Sigma Orionis, the blue star seen just "above" the Horsehead Nebula, appears to have blown a "hole" around itself in the bright red-glowing ionized hydrogen that surrounds it. This is indeed what hot massive stars do: how else would the Rosette Nebula have gotten its shape?

And all those "brownish" tendrils of gas filling so much of the scene get their color from hydrogen at low levels of ionization. Almost the entire skyscape here is filled with glowing hydrogen.

What a great picture!

Ann

Some of the brown clouds are indeed dust clouds that are illuminated by the many bright stars in this region. Some of these dust clouds are remnant molecular clouds that have run out of gas to form more stars. Some of them were catalogued by the Japanese astronomers Katsuo Ogura and Koji Sugitani in 1998 as the OS catalogue. Their paper can be viewed here: http://cdsads.u-strasbg.fr/abs/1998PASA...15...91O
They can also be identified in this image by Fabian Neyer: http://www.starpointing.com/ccd/orion_labeled.html

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ann » Tue Oct 29, 2013 2:02 pm

starsurfer wrote:
Ann wrote:This is a great mosaic! :D

To me as a color commentator, the colors are of course particularly interesting here. Note how Sigma Orionis, the blue star seen just "above" the Horsehead Nebula, appears to have blown a "hole" around itself in the bright red-glowing ionized hydrogen that surrounds it. This is indeed what hot massive stars do: how else would the Rosette Nebula have gotten its shape?

And all those "brownish" tendrils of gas filling so much of the scene get their color from hydrogen at low levels of ionization. Almost the entire skyscape here is filled with glowing hydrogen.

What a great picture!

Ann

Some of the brown clouds are indeed dust clouds that are illuminated by the many bright stars in this region. Some of these dust clouds are remnant molecular clouds that have run out of gas to form more stars. Some of them were catalogued by the Japanese astronomers Katsuo Ogura and Koji Sugitani in 1998 as the OS catalogue. Their paper can be viewed here: http://cdsads.u-strasbg.fr/abs/1998PASA...15...91O
They can also be identified in this image by Fabian Neyer: http://www.starpointing.com/ccd/orion_labeled.html


Thanks, starsurfer, very interesting! :D :D :D

It makes perfect sense that there should be "incipient dust pillars, elephant trunks or cometary globules" near the Orion Nebula. It makes perfect sense, too, that the dust pillar near Alnilam should be the most well-developed one, since Alnilam is clearly older than the stars in or near the Orion Nebula and the Horsehead region.

In Fabian Neyer's beautiful and extremely informative image, the region between the Horsehead and M42 is reddish, clearly from Ha emission. All the "incipient pillar structures" between the Horsehead and M42, OS 31, OS 61, SFO 21, LBN 967, OS 30, OS 36, KKY 76, OS 60 A and B, OS 59, SFO 22, OS 45, OS 46, OS 47, OS 56, HH 221 and HH 401, have red Ha-bright rims.

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby ThedaCranberry » Tue Oct 29, 2013 2:04 pm

This is how I oxygenate myself in the morning: a sigh of wonder when I view the picture, then laughing in amazement at the arcane discussions. Thank you, APOD. I sure missed you during the shutdown.

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby brywalker » Tue Oct 29, 2013 3:12 pm

I used the UK mirror to get thru the shutdown,
http://www.star.ucl.ac.uk/~apod/apod/astropix.html
As a rank amateur my question is this:
Assuming they are not in the picture, where would the other belt stars, Alnilam and Mintaka, be in relation to this picture?
Please assume zero knowledge in attempting to answer!
Thanks!

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby neufer » Tue Oct 29, 2013 4:57 pm

brywalker wrote:
Assuming they are not in the picture, where would the other belt stars,
Alnilam and Mintaka, be in relation to this picture?

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Beyond » Tue Oct 29, 2013 6:00 pm

Thanks neufer. At first i thought, Oh Great :!: A close up. How the heck can anyone tell anything from that :?: Then, after a bit of staring... Oh yeah, there's the Horsehead, almost upside down. Hope it's fodder don't fall out. :lol2:
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ann » Tue Oct 29, 2013 6:00 pm

brywalker wrote:I used the UK mirror to get thru the shutdown,
http://www.star.ucl.ac.uk/~apod/apod/astropix.html
As a rank amateur my question is this:
Assuming they are not in the picture, where would the other belt stars, Alnilam and Mintaka, be in relation to this picture?
Please assume zero knowledge in attempting to answer!
Thanks!


Check out this annotated version of Rogelio Bernal Andreo's mosaic of constellation Orion, brywalker.

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby BMAONE23 » Tue Oct 29, 2013 7:19 pm

Beyond wrote:Thanks neufer. At first i thought, Oh Great :!: A close up. How the heck can anyone tell anything from that :?: Then, after a bit of staring... Oh yeah, there's the Horsehead, almost upside down. Hope it's fodder don't fall out. :lol2:

I don't tink it's da fodder yous needs to worry about, its da mudder dats of concoin

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Beyond » Tue Oct 29, 2013 7:51 pm

BMAONE23 wrote:
Beyond wrote:Thanks neufer. At first i thought, Oh Great :!: A close up. How the heck can anyone tell anything from that :?: Then, after a bit of staring... Oh yeah, there's the Horsehead, almost upside down. Hope it's fodder don't fall out. :lol2:

I don't tink it's da fodder yous needs to worry about, its da mudder dats of concoin

Not ifin youse only runs dem on dry tracks. :lol2:
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Anthony Barreiro » Tue Oct 29, 2013 9:29 pm

Ann wrote:
brywalker wrote:I used the UK mirror to get thru the shutdown,
http://www.star.ucl.ac.uk/~apod/apod/astropix.html
As a rank amateur my question is this:
Assuming they are not in the picture, where would the other belt stars, Alnilam and Mintaka, be in relation to this picture?
Please assume zero knowledge in attempting to answer!
Thanks!


Check out this annotated version of Rogelio Bernal Andreo's mosaic of constellation Orion, brywalker.

Ann

That is an awesomely beautiful picture! Has this ever been an apod? (Hint, hint.)
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ron-Astro Pharmacist » Tue Oct 29, 2013 9:30 pm

Or if you find it on the pilla' next to you.... :ohno:
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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby BMAONE23 » Tue Oct 29, 2013 9:34 pm

Or per'aps b'tween da sheets. At least dat horse quit while it was ahead

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby saturno2 » Tue Oct 29, 2013 10:03 pm

Beautiful image and very interesting.
A spirited horse riding in the vicinity of Alnitak in Orion

Guest

Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Guest » Wed Oct 30, 2013 4:10 pm

Check out this annotated version of Rogelio Bernal Andreo's mosaic of constellation Orion, brywalker.

Ann[/quote]

Thank you all, especially Ann,
so IF I am now correct Alnilam and Mintaka would be off the screen upwards to the left.
Bry

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Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby Ann » Wed Oct 30, 2013 8:16 pm

Guest wrote:Thank you all, especially Ann,
so IF I am now correct Alnilam and Mintaka would be off the screen upwards to the left.
Bry


That's correct, Bry! :D

Ann
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brywalker

Re: APOD: Horsehead and Orion Nebulas (2013 Oct 29)

Postby brywalker » Fri Nov 01, 2013 6:28 pm

Ann wrote:
Guest wrote:Thank you all, especially Ann,
so IF I am now correct Alnilam and Mintaka would be off the screen upwards to the left.
Bry


That's correct, Bry! :D

Ann



Thanks so much!
Bry
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