APOD: NGC 7822 in Cepheus (2011 Nov 16)

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APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by APOD Robot » Wed Nov 16, 2011 5:09 am

Image NGC 7822 in Cepheus

Explanation: Hot, young stars and cosmic pillars of gas and dust seem to crowd into NGC 7822. At the edge of a giant molecular cloud toward the northern constellation Cepheus, the glowing star forming region lies about 3,000 light-years away. Within the nebula, bright edges and dark shapes are highlighted in this colorful skyscape. The image includes data from narrowband filters, mapping emission from atomic oxygen, hydrogen, and sulfur into blue, green, and red hues. The atomic emission is powered by energetic radiation from the hot stars, whose powerful winds and radiation also sculpt and erode the denser pillar shapes. Stars could still be forming inside the pillars by gravitational collapse, but as the pillars are eroded away, any forming stars will ultimately be cutoff from their reservoir of star stuff. This field spans around 40 light-years at the estimated distance of NGC 7822.

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don.s

Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by don.s » Wed Nov 16, 2011 7:04 am

How about showing some if these pic's in absolute real color as they appear in real life?

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Ann
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Ann » Wed Nov 16, 2011 7:20 am

Image
Here is a picture which may give you some idea of what the nebula might look like in "real color". :arrow:

You may want to check out this link, too.

I'm very much a fan of "real color" myself! But in the case of NGC 7822, it would be hard to spot the "real color" of the nebula in the first place if you managed to "visit the nebula", because the gas cloud is really thin and tenuous, and the light it emits is far into the red part of the spectrum, where the sensibility of the human eye is low. Just possibly, you might be able to see some wisps of blue-green light from hydrogen beta emission, because our sensitivity to green light is much greater than to red. But most of the light emitted by the nebula is narrowband light around 656 nm, which corresponds to deep red light.

However, what you would see most clearly if you were anywhere near a nebula like this one would be the brilliant (bluish) light of the stars that make the nebula glow.

Ann
Last edited by Ann on Wed Nov 16, 2011 4:08 pm, edited 1 time in total.
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by moontrail » Wed Nov 16, 2011 9:00 am

don.s wrote:How about showing some if these pic's in absolute real color as they appear in real life?
Are most of astronomy pictures real for the naked eye?
Discussed at http://asterisk.apod.com/viewtopic.php?f=8&t=22430

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by orin stepanek » Wed Nov 16, 2011 2:15 pm

One of the reasons I like APOD is that they show these views in color! Todays is really neat. It goes into my background collection! 8-) :lol: :)
Orin

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Chris Peterson » Wed Nov 16, 2011 2:20 pm

don.s wrote:How about showing some if these pic's in absolute real color as they appear in real life?
They show no color to the eye, and precious little structure, even with a large telescope. The reason we image is because it allows us to get a much better "picture" of what something is really like than we can ever do with our eyes- aided by a telescope or not.
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by moonstruck » Wed Nov 16, 2011 3:40 pm

don.s wrote:How about showing some if these pic's in absolute real color as they appear in real life?
How about just going outside in real life and looking up at it :?

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by BMAONE23 » Wed Nov 16, 2011 3:56 pm

The Human Eye has a visual refresh rate of 1/30th of a second. 30 times a second images are sent to our visual cortex for processing. This is how we discern motion. Movies are shot at a rate of 32 frames per second to replicate this effect on the "Big Screen".

If you set the Camera Shutter Speed to 1/30th of a second, you could only ever produce images exactly as they would be seen by the naked eye and would basically see exactly the same thing in the pictures as you do when you go out and look up at night.

When you go out at night and look up at Orion:
Do you see Bernard’s Loop?
Do you see the Horse Head?

Do you see the majesty of Andromeda which is wider than 3 full moons?

Many structures remain hidden without:
Magnification to gather more light
Deeper Imaging (longer shutter speeds) to gather more light
Special Filters to image finer structures and other wavelengths

Imaging “As we see them” would really reveal nothing more than what you already see when you look up at the sky at night.

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Case » Wed Nov 16, 2011 5:57 pm

BMAONE23 wrote:Movies are shot at a rate of 32 frames per second to replicate this effect on the "Big Screen".
<nitpick>
That would be 24 fps, which was an upgrade from the old 16 fps of the silent era. 24 was just a convenient number close enough to what the human eye processes, while also being nicely divisible for easy calculation from frames to seconds. Peter Jackson is experimenting with 48 fps for the upcoming ‘The Hobbit’, although I wonder if enough theaters (read: theaters close to me) are capable of showing it that way.

Why are movies filmed @ 24 FPS?
</nitpick>

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by geckzilla » Wed Nov 16, 2011 6:52 pm

They do say it's pointless to view anything above one's natural refresh rate, but when I play games I definitely notice that it seems smoother at 60 or even 100 FPS.
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Case » Wed Nov 16, 2011 7:25 pm

geckzilla wrote:They do say it's pointless to view anything above one's natural refresh rate, but when I play games I definitely notice that it seems smoother at 60 or even 100 FPS.
People in the field have argued that such is because games do not have motion blur (what movement would happen during the recording and display of a single frame), while film does have the perception of smooth motion due to motion blur.
I, for one, like Roman numerals.

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by BMAONE23 » Wed Nov 16, 2011 9:20 pm

Thanks for the Nit Wit Case
I always thought that it went from 8 to 16 to 32 Guess I was thinking mm film size and not speed FPS

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by mst66186 » Thu Nov 17, 2011 1:32 am

APOD Robot wrote:Image NGC 7822 in Cepheus
In the top-middle of the picture is a dark cloud. Is that at the same distance as the nebula (i.e. is it a part of the nebula, lit on the side facing away from us, or is it just an intervening dark cloud)?

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Ann
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Ann » Thu Nov 17, 2011 1:51 am

mst66186 wrote:
APOD Robot wrote:Image NGC 7822 in Cepheus
In the top-middle of the picture is a dark cloud. Is that at the same distance as the nebula (i.e. is it a part of the nebula, lit on the side facing away from us, or is it just an intervening dark cloud)?
It is almost certainly a part of the nebula. Remember that you can't have a nebula at all if you don't have a gas cloud to start with, and the gas cloud always contains tiny particles of dust. If the gas cloud becomes sufficiently concentrated - as it must, if it is undergoing gravitational collapse, which may give rise to new stars - then the dust will become concentrated too. And then the dust will make the gas cloud look quite black.

Check out http://asterisk.apod.com/viewtopic.php?f=29&t=22862, and you will see not only today's APOD there (if you scroll down a bit), but you will also find images of starforming regions NGC 1333 and NGC 2170. In these pictures you can see glowing, luminous gas clouds as well as dark dust clouds.
Take a look at cluster NGC 6520, which you can see at center left in this image. To the right of it, you can see a very dark cloud.

Before this cluster was born, there must have been a very big, massive gas cloud here. When the first hot bright were born, the gas cloud must have lit up as a glorious nebula. But that was a long time ago. The hot stars of NGC 6520 have cooled and turned into red giants, which can't make a gas cloud light up (with the exception of Antares, which creates a yellow reflection nebula). The blue stars that remain are of spectral class A or cooler. We can't even be sure that the dark cloud to the right of this cluster is a remnant of the original starforming nebula. It might be such a remnant. Whether or not it is, the dark cloud is clearly fairly small and light-weight, and it can't give birth to more than, at best, small cool stars, smaller than the Sun.

Ann
Last edited by Ann on Thu Nov 17, 2011 4:48 pm, edited 3 times in total.
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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by DavidLeodis » Thu Nov 17, 2011 2:30 pm

It's a wonderful image. It also seems like it's a view looking up a tube. :)

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Re: APOD: NGC 7822 in Cepheus (2011 Nov 16)

Post by Chris Peterson » Thu Nov 17, 2011 2:48 pm

BMAONE23 wrote:The Human Eye has a visual refresh rate of 1/30th of a second. 30 times a second images are sent to our visual cortex for processing.
This is not true. The eye continually sends data to the visual cortex. The photosensitive cells in the retina have integration times on the order of 10-100 ms, which means that the eye behaves something like a camera with an exposure time range of 1/10 to 1/100 second. But this doesn't impact our ability to sense motion, because there is no synchronization between the cells or in our processing.
If you set the Camera Shutter Speed to 1/30th of a second, you could only ever produce images exactly as they would be seen by the naked eye and would basically see exactly the same thing in the pictures as you do when you go out and look up at night.
There are many other factors: cameras typically have a higher quantum efficiency than the eye (they record more of the incident photons), cameras are much more efficient integrators, the eye is low resolution, but because it moves around, the resulting image as constructed in the brain is very high resolution, and our processing is very sensitive to subtleties that static camera images miss.
Many structures remain hidden without:
Magnification to gather more light
Magnification doesn't gather more light. A larger aperture gathers more light, which is important for imaging. When you use a telescope visually, it can never produce an image brighter than the naked eye sees, however.
Chris

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