APOD: Clouds in Cygnus (2012 Nov 30)

Comments and questions about the APOD on the main view screen.
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APOD: Clouds in Cygnus (2012 Nov 30)

Post by APOD Robot » Fri Nov 30, 2012 5:06 am

Image Clouds in Cygnus

Explanation: Cosmic clouds of gas and dust drift across this magnificent mosaic covering a 12x12 degree field within the high flying constellation Cygnus. The collaborative skyscape, a combination of broad and narrow band image data presented in the Hubble palette, is anchored by bright, hot, supergiant star Deneb, below center near the left edge. Alpha star of Cygnus, Deneb, is the top of the Northern Cross asterism and is seen here next to the dark void known as the Northern Coal Sack. Below Deneb are the recognizable North America and Pelican nebulae (NGC 7000 and IC 5070). Another supergiant star, Sadr (Gamma Cygni) is near the center of the field just above the bright wings of the Butterfly Nebula. A line continuing up and right will encounter the more compact Crescent Nebula and finally the Tulip Nebula near the top of the frame. Most of these complex nebulosities are located about 2,000 light-years away. Along with the Sun, they lie in the Orion spiral arm of our Milky Way galaxy.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by ta152h0 » Fri Nov 30, 2012 5:49 am

looks like a scorpion crawling down the screen from the upper right in the direction of lower left, or not
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by revloren » Fri Nov 30, 2012 6:23 am

I see jellyfish swimming in a see of kelp. :fish:

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by BDanielMayfield » Fri Nov 30, 2012 1:45 pm

Why do the colors in this apod look so unusual? The nebulas are very recognizable by shape, but not by color.
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by bystander » Fri Nov 30, 2012 4:01 pm

BDanielMayfield wrote:Why do the colors in this apod look so unusual? The nebulas are very recognizable by shape, but not by color.
APOD Robot wrote: a combination of broad and narrow band image data presented in the Hubble palette,
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by FloridaMike » Fri Nov 30, 2012 6:27 pm

This looks like one big cloud of material to me. So the various nebula are just different illuminated regions of an overall structure? And the only significance of the "X", "Y" or "Z" nebula is that an observer concluded "I can name that shape" seen in a particular region?

I guess it makes sense, it is just not how I had envisioned it. The nebula names function more like landmarks instead of identifying a unique entity.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by neufer » Fri Nov 30, 2012 7:08 pm

bystander wrote:
BDanielMayfield wrote:
Why do the colors in this apod look so unusual? The nebulas are very recognizable by shape, but not by color.
APOD Robot wrote: a combination of broad and narrow band image data presented in the Hubble palette,
http://en.wikipedia.org/wiki/Palate wrote:
The palate [L. palatum, properly the arch or cope of heaven.] the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate.
http://en.wikipedia.org/wiki/Palette_%28painting%29 wrote:
Palette [F. palette: af. It. paletta; prop. and orig., a fire shovel.] a rigid, flat surface on which a painter arranges and mixes paints. The most commonly known type of painter's palette is made of a thin wood board designed to be held in the artist's hand and rest on the artist's arm.
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by emc » Fri Nov 30, 2012 8:18 pm

I had me a turkey and egg sandwich for lunch but I don’t know what my pal ate.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by ta152h0 » Fri Nov 30, 2012 8:21 pm

I had bacon fried rice and won-tons
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by dlw » Fri Nov 30, 2012 8:25 pm

revloren wrote:I see jellyfish swimming in a see of kelp. :fish:
So what -is- that little jellyfish? It is so well defined and seemingly symmetrical.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by Boomer12k » Fri Nov 30, 2012 8:29 pm

Looks like a Dragon.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by BMAONE23 » Fri Nov 30, 2012 9:59 pm

dlw wrote:
revloren wrote:I see jellyfish swimming in a see of kelp. :fish:
So what -is- that little jellyfish? It is so well defined and seemingly symmetrical.
It is NGC 6888
otherwise known as the Crescent Nebula. Here are two other close-up views from earlier APOD's
http://apod.nasa.gov/apod/ap120816.html http://apod.nasa.gov/apod/ap090915.html
Last edited by bystander on Fri Nov 30, 2012 11:17 pm, edited 1 time in total.
Reason: replaced full-size 'click-thru' images with display images for faster loading

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by Beyond » Sat Dec 01, 2012 1:59 am

To me, it looks like Cygnus is in desperate need of a vist from the Hoover nebula. :mrgreen:
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by ta152h0 » Sat Dec 01, 2012 4:04 am

with the understanding one sometimes is humorous, I would like to see the Marylin Monroe nebula coming to visit
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by Beyond » Sat Dec 01, 2012 4:35 am

Nebuosity can be quite fun at times! :lol2:
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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by Ann » Sat Dec 01, 2012 6:23 am

BDanielMayfield wrote:Why do the colors in this apod look so unusual? The nebulas are very recognizable by shape, but not by color.
The colors look strange because they have been produced with narrowband photography. Narrowband photography does not produce colors the way the human eye is built to detect it. We have blue-, green- and red-sensitive "color detectors", so called cones. Their ranges of sensitivity overlap, which is why we can detect an enormous range of hues.

Narrowband photography means that you photograph only extremely specific wavelengths, for example hydrogen alpha at 656 nm. Hydrogen alpha emission completely dominates almost all emission nebulae. This means that if you were to photograph the region of Cygnus near Deneb and Sadr through a hydrogen alpha filter, your entire image would be flooded by red, all of it exactly the same shade of red.

There is another emission line whose color is almost exactly the same as hydrogen alpha, ionized sulphur, SII. SII is just a little deeper into the red part of the spectrum than Ha. Visually, there is actually no difference between them. However, SII emission is generally fainter than Ha, and more importantly, it represents a lower grade of ionization than Ha. Where you have SII emission but no Ha, you are likely to be relatively far away from the ionization source.

For scientific purposes, then, it might be useful to separate the Ha emission from the SII, but you can't do that using ordinary RGB astrophotography. However, with narrowband photography you can indeed separate the two. You can take one image through a Ha filter and one image through an SII filter, and they will indeed look different. You can then combine the two images into one picture. But when doing so, it is customary to assign different colors to the Ha picture and the SII picture. In reality both are red. But to separate them, it is customary, using the Hubble palette, to assign green color to the Ha image.

There is another emission line which is of interest, and that is the OIII line. Whereas the SII line represents are fairly low degree of ionization, OIII is only found where ionization is high. Therefore it is popular to make images through an OIII emission to isolate regions where the degree of ionization is very high. The true color of OIII emission is blue-green, but when OIII images are combined with Ha and SII images, the OIII image is colored blue.

Here is a (very large) picture of a nebula in Cygnus which has been produced with narrowband photography in the Hubble palette. Blue represents high-ionization OIII emission, green is Ha and red is low-ionization SII.

Do you want to know what today's APOD would look like to our eyes, if our eyes were sensitive enough to detect color in nebulae? This is what it would look like.

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Re: APOD: Clouds in Cygnus (2012 Nov 30)

Post by BDanielMayfield » Sun Dec 02, 2012 5:17 am

Thanks Ann! That was exactly the kind of detailed answer I was seeking.
Ann wrote: Do you want to know what today's APOD would look like to our eyes, if our eyes were sensitive enough to detect color in nebulae? This is what it would look like.

Ann
Wow, to my eyes that is a MUCH more attractive photo! That's going to replace the Iris Nebula as my new wallpaper. Thanks again very much.

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