APOD: Clouds of Perseus (2011 Oct 21)

[APOD Robot]

Clouds of Perseus

Explanation: Cosmic clouds of gas and dust drift across this magnificent panorama, spanning some 17 degrees near the southern boundary of the heroic constellation Perseus. The collaborative skyscape begins with bluish stars of Perseus at the left, but the eye is drawn to the striking, red NGC 1499. Also known as the California Nebula, its characteristic glow of atomic hydrogen gas is powered by ultraviolet light from luminous blue star Xi Persei immediately to the nebula's right. Farther along, intriguing young star cluster IC 348 and neighboring Flying Ghost Nebula are right of center. Connected by dark and dusty tendrils on the outskirts of a giant molecular cloud, another active star forming region, NGC 1333, lies near the upper right edge of the wide field of view. Shining faintly, dust clouds strewn throughout the scene are hovering hundreds of light-years above the galactic plane and reflect starlight from the Milky Way.

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[mexhunter]

In the words of Mr. Spock: fascinating.
Congratulations Rogelio, it is an beautiful image.
Greetings!

[Ann]

Oh, that's just a fantastic image! So incredibly deep! So very wide! Such amazing colors!

That's wonderful!!!

Ann

[islader2]

That's William Walker's Baja California Sur==not Fremont's Republic. Note both coasts. {Thanx, Rogelio--a work of art}.

[starstruck]

I just luuurve this APOD! . . . feels like being lost in space!

. . it's a totally "super-wow-awesome" collaboration guys, thanks for the high res panorama

[StefanoDeRosa]

Really a stunning image

Stefano

[alphachap]

A lot more here: http://blog.deepskycolors.com/nebulas.html

[Boomer12k]

And in the California Nebula, I see a Shark, and a running Scotty Terrier.....no kidding....


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[sOnIc]

I've been here before, and I will be unpopular, but my opinion is that these images are a bad idea. Correct me if I'm wrong, but this again is a graphical illustration - the Cali nebula Ha region is far too bright, superimposed upon a background... Why is the Cali nebula significantly brighter than the Ha region on the right? The reddish part of the NGC1333 is at a realistic and correct balance with its surroundings, the Cali nebula is far too bright and looks like what it is: an overlay. Imagine if you did an RGB image of this region with IR block removed so you can pick up the Ha red, that's recording what is actually there, the difference is that this picture has an Ha image overlaid in an un-naturally bright way, beyond what astrophotographers would normally use. The background is wonderful, the foreground is wonderful, but why merge them with such unrealistic brightness balance? Unless purely to show the scale of the object. I find these 'overlay' images to be false and misleading.

(The link posted above by alphachap shows lots of examples of great astrophotography/processing, yes all using overlays of channels with some artistic licence, but not overdone like this APOD.
As an example this super deep image looks natural to me, just the right amount of Ha red)

[neptunium]

Hey, a cool image! Rogelio, you have done it again! The California Nebula looks stunning, along with those other clouds of gas and dust.

[orin stepanek]

I'm like Mikey; I liked it! Perseus is one of those constellations that I have trouble connecting the dots (stars) to in the night sky. So I looked it up.

Click to view full size image

[neufer]

Perseus is one of those constellations that I have trouble connecting the dots (stars) to in the night sky.
So I looked it up.

Too bad the red blood stain on Perseus' sword does not correspond to the California Nebula. Apparently Perseus cut "the right foot of Andromeda ... " since the blood stain corresponds much more to M76, (the so called "Nebula at the right foot of Andromeda."). The California Nebula is down near the left calf of Perseus: Xi Persei (ξ Per) with the traditional name Menkib (Arabic, of course, for "shoulder" [of the Pleiades]). Menkib is classified Ann's type of star: a blue giant (spectral class O7.5III) so it needs to be juxtaposed with something red like Perseus's red skirt.

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<<This infrared image from NASA's Wide-field Infrared Survey Explorer, or WISE, features one of the bright stars in the constellation Perseus, named Menkhib (at upper left near the red dust cloud), along with a large star-forming cloud NGC 1499, or the California nebula, seen running diagonally through the image.

Menkhib is one of the hottest stars visible in the night sky; its surface temperature is about 37,000 Kelvin (more than six times hotter than the sun). Because of its high temperature, it appears blue-white to the human eye (almost all stars appear bluish to WISE). It has about 40 times the mass of the sun and gives off 330,000 times the amount of light. Menkhib is a runaway star, and the fast stellar wind it blows is piling up in front of it to create a shock wave. This shock wave is heating up dust, which WISE sees as the red cloud in the upper left of the image.

Menkhib is part of an association of very hot stars that were born from the California nebula only a few million years ago. These stars are lighting up the nebula, as wekk as heating and ionizing it. In visible light, the ionized gas glows red, while in infrared light we see the heated dust (which appears in green and red in this image). The California nebula gets its name due to a resemblance to the shape of the U.S. State California (which you can just make out, outlined by the green dust, if you rotate the image by a little more than 90 degrees clockwise). The entire California nebula stretches across about 100 light-years, and we see about 80 percent of it in this view.

Menkhib and the California nebula are about 1,800 light-years away from Earth. This is within the same spur of the Orion spiral arm of the Milky Way galaxy where we are located.

All four infrared detectors aboard WISE were used to make this image. Color is representational: blue and cyan represent infrared light at wavelengths of 3.4 and 4.6 microns, which is dominated by light from stars. Green and red represent light at 12 and 22 microns, which is mostly light from warm dust.>>

[Chris Peterson]

I've been here before, and I will be unpopular, but my opinion is that these images are a bad idea...

In many respects, I agree with you. This image reflects a current trend in aesthetic astroimaging, which emphasizes highly saturated colors and a lack of photometric and colorimetric integrity across the image. But the key point here is that this image is primarily intended to be aesthetic, not scientific. So it represents an artistic vision by its creators- which we may individually connect with or not, just like any art. That's not a fault, unless the image is represented as scientific- which I don't think is the case here. Certainly, APOD images, by design, span a wide range from hard science to pure art.

Aesthetics aside, the image demonstrates masterful processing skills, as well as some very dedicated imaging (I'd actually use the term "masochistic", given the authors' use of refractors for their scopes and field imaging, rather than the use of dedicated observatories!)

[StarCuriousAero]

What a lovely panarama, especially how the nebula on the right is showing up purple! Is this a result of red hydrogen/emission nebula light combining with blue star/reflection nebula light? I don't know if I've ever seen (or noticed) a purple nebula before, hmmm.

Think I'll have to crop this image somehow to make it my new desktop background in any case, certainly a very striking image. And I definitely don't agree with that guy above saying the California Nebula is too bright (even if it's not "natural") because it really brings out the detail! Much easier to admire wispy filaments when it's brighter and sharper. There's a valuable purpose to being able to digitally process astro-photography, and it certainly has a place here in my book.

[sOnIc]

I don't know if I've ever seen (or noticed) a purple nebula before, hmmm.

My point exactly ... I'm not moaning about processing, all narrowband imaging has artistic input, I just think this one has gone too far, and thus you get confussion about purple nebulae ^ ! Why are they different? Because the two Ha regions have very different processing.

[Ann]

I don't know if I've ever seen (or noticed) a purple nebula before, hmmm.

My point exactly ... I'm not moaning about processing, all narrowband imaging has artistic input, I just think this one has gone too far, and thus you get confussion about purple nebulae ^ ! Why are they different? Because the two Ha regions have very different processing.

There is nothing strange about them being different.

Menkib, Xi Persei, the blue star ionizing the bright red California Nebula, is a star of spectral class O7.5Iab. That means that the star is extremely hot - about 37,000 degrees Kelvin - as well as very large, and it produces copious amounts of ultraviolet light. All those ultraviolet photons ionize the hydrogen in the California Nebula and make it glow red.

The purple nebula, by contrast, is found close to bright star Omicron Persei of spectral class B1III. While hot, this star is probably at least 10,000 degrees Kelvin cooler than Xi Persei, and it is very much more inefficient at ionizing the hydrogen close to it. In fact, it may be too cool to do any noticeable ionizing at all. But the star produces copious amounts of blue light which is reflected in in the dust which surrounds this region, probably over a distance of many light-years.

The purple nebulosity is strongly associated with star forming region IC 348. IC 348 appears to be a typical low-mass star formation region. That means that it produces small, light-weight stars. Even small stars have outbursts during the processes in which they form, and therefore they give rise to smallish jets, which ionize hydrogen around them and make it glow pink. In the case of IC 438 we aren't seeing the jets directly. Instead we see low levels of ionized hydrogen permeating this entire star formation region and making it glow pink. This pink light is mixed with blue star light reflected from the bright stars in the region (and possibly from stars inside IC 348 itself). Pink light plus blue light makes purple light.

The reason why the California nebula is so much redder than IC 348 is that the level of ionization, the number of ultraviolet photons and the number of hydrogen atoms being ionized by them, is so much higher in the California Nebula than in IC 348.

Ann

[Rogelio Bernal]

For whatever is worth...

Color processing to this image has been done uniformly across the whole image. No selective color adjustments or "color picker" operations have been done.

Being a mosaic, I would expect that color calibration may show some differences between panes, as the 10 panes were captured with cameras of different sensitivity and at nights of different atmospheric conditions, despite we tried to account for all this. In any case, any differences wouldn't be particularly dramatic so as to make "purple" something that should have probably appeared "red".

The entire 2x5 mosaic used LRGB data. The panes comprising NGC 1499 also included H-Alpha data. Ha+ RGB integration was done at the linear stage, with the proper rescaling options to ensure some balance between the existing RGB data and the added H-Alpha data. So the assertion that the nebula has been "superimposed upon a background" is misleading. A more correct statement would be that data from different filters has been integrated for this particular region.

This didn't in fact add more "red" to NGC1499 (you could process just the RGB data and it will probably have an even more "pure" red color), it mainly emphasized the structures in the nebula and its visibility. The California nebula REALLY is much brighter than its surroundings - a linear stretch would saturate the nebula immediately, while the surrounding dust would still be barely visible, if at all. In other words, if the California nebula appeared less bright in this image - which is what I think some people may feel it would be "more natural" or "realistic" - that could actually be even more "misleading" than today's APOD image. A non-linear stretch can easily throw all that away, yet there really isn't any "blame" being thrown at that - it's just our perception: the nebula is WAY TOO BRIGHT. Well, it is. And proportionally to all other structures, it is even brighter than that.

But let's leave that aside...

The biggest attention-grabber in NGC 1499 is not the color, which is what it is - red - and I've already mentioned its brightness as well. It's the high level of color saturation. Color and saturation are different things and must not be mistaken. Still, color saturation too was applied uniformly to the entire image, with the only exception of star color for which saturation was adjusted separately. All dust and nebulae in the image received the same amount of color saturation - every single pixel. A toned-down saturation would show most of the dust of a much pale color. By pushing saturation it, it can be argued that one could actually learn more than if the image was less saturated. What some find misleading, I find it to add value, but of course, I won't expect everyone to understand "value" equally, and there's nothing wrong with that.

Still, I would like to add that one of the reasons for the strong saturation (again, applied globally to the entire image) is actually not so much for aesthetic impact but because this image will be printed on a duratran-like transparency, and usually, it is a good idea to increase color saturation for this type of media. Once the image was finished, I personally felt it also looked "good enough" for web presentation and I decided to leave it as it is.

Ad yes Chris, there's something a bit masochist about all this

Regards,
Rogelio

[islader2]

@ ROGELIO Your photo IS excellent==and the explanation is just as great. In me,you have a true fan. Thanx.
Owlice: Sorry for the second post today, but I do not keep count of my posts. I come to admire good entries.

[Ann]

@ ROGELIO Your photo IS excellent==and the explanation is just as great. In me,you have a true fan. Thanx.

In me, too. Rogelio. And thank you very much for your explanation. So you have decreased the brightness of the California Nebula in order to make the other dust structures visible. That makes perfect sense, while at the same time it is very good that you mention it.

As for the nebular color, it is very good that it has been treated and processed in the same way over the entire field, so that it really shows how the dust and gas changes color over the the entire field.

I agree with you that there just has to be some scientific value to that. And the picture is just stunningly beautiful and incredibly deep and revealing.

Ann

[Rogelio Bernal]

Just a quick note that, although it was reflected in the credits, this is not just MY photo but a collaborative effort between four people, and although I processed the version you see, I assure you everyone worker very hard on the project. In fact the amount of data in the image that I captured accounts for just 1/4 of it approximately, so there's 3/4 of it for which Bob, Al and Eric deserve equal recognition. And while I was processing the image, everyone was sharing their impressions, etc. Working on this collaborative project has been hard work for all of us, but we all also had a lot of fun.
Cheers!
Rogelio

[sOnIc]

Firstly, I am sorry for jumping to conclusions regarding the purple nebula, I made an incorrect assumption that it was the same process as the Californian Nebula's Ha emission's, I stand corrected; nice explanation Ann And, thank you Rogelio for your detailed explanation too, the processing is fantastic; these kind of images are getting deeper all the time as the technology and techniques improve.

The reason I commented was in instant reaction in seeing this image - "mm something not right" - and that is still there for me. The best example is that I do NOT get that impression from this version; in which the colours are still very bright yet somehow more uniformed across the field, notice the purple nebula is not so different here. I've commented before on some images where one particular layer is either overdone or actually used masking in a very misleading way, and I assumed the same of this since the red Cali nebula stands out so much from the rest of the image, it is certainly unusual to see these faint emissions stand out so much.

Either way, these deep sky images are wonderful and a huge credit to everyone involved : )

[Rogelio Bernal]

The reason I commented was in instant reaction in seeing this image - "mm something not right" - and that is still there for me. The best example is that I do NOT get that impression from this version; in which the colours are still very bright yet somehow more uniformed across the field

I think that's perfectly understandable. The dynamic range in these FOVs is huge, and when we break the linearity of the data, we tend to "balance" it into a somewhat uniform range. It's true that the other example you point out reflects that uniformity, but I'd also say that when I did that image, I was a total rookie in many aspects

I think we are just trained to see things in a certain way. For example, looking at this image from Palomar:

Click to view full size image

we see NGC 1499 nicely balanced with the background. Not too bright, not too dark... It seems just right.

Now, theoretically, if we were to stretch this image (increase its brightness) so as to bring out the surrounding dust clouds, how bright would NGC 1499 have to become? Likely a lot brighter than in yesterday's image - and let's not forget, the above snapshot from Palomar isn't representing "real" brightness either, just a "comfortable brightness". So my point is only that, while some may feel that the proportional brightness of NGC 1499 against its surroundings in yesterday's image may seem "misleading", the way I see it is that the fact it is so much brighter than what we might consider "appropriate" is in fact less misleading, because the proportional brightness of NGC 1499 is closer to "reality", and when our brain demands a toned down nebula because it would feel as a "more accurate representation and less aesthetics" can in fact only be resolved by further distorting "reality" in favor of, yes, aesthetics. That's how I see it at least.

Or something like that