APOD: Persistent Saturnian Auroras (2014 Jun 22)

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APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by APOD Robot » Sun Jun 22, 2014 4:08 am

Image Persistent Saturnian Auroras

Explanation: Are Saturn's auroras like Earth's? To help answer this question, the Hubble Space Telescope and the Cassini spacecraft monitored Saturn's South Pole simultaneously as Cassini closed in on the gas giant in January 2004. Hubble snapped images in ultraviolet light, while Cassini recorded radio emissions and monitored the solar wind. Like on Earth, Saturn's auroras make total or partial rings around magnetic poles. Unlike on Earth, however, Saturn's auroras persist for days, as opposed to only minutes on Earth. Although surely created by charged particles entering the atmosphere, Saturn's auroras also appear to be more closely modulated by the solar wind than either Earth's or Jupiter's auroras. The above sequence shows three Hubble images of Saturn each taken two days apart.

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Marvin » Sun Jun 22, 2014 5:15 pm

I don't wish to question the integrity of this picture - fascinating evolution of the aurorae. However, the 'Saturns' appear to be identical. It may be processing errors, but the same pattern of small dark/light spots on the visible surface of Saturn appear in all three elements - was this a combination of differing aurorae on the same background Saturn? I may well have the wrong end of the stick, but is Saturn's rotation so slow that 'surface' features would not have perceptibly moved over 3 earth days? Sorry if this sounds ignorant, but I'm genuinely puzzled?

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Sun Jun 22, 2014 5:55 pm

Marvin wrote:I don't wish to question the integrity of this picture - fascinating evolution of the aurorae. However, the 'Saturns' appear to be identical.
Good catch. The visible light image of Saturn was captured two months after the three UV images of the auroras. That single image of Saturn is simply being used as a template so that we can easily visualize the location and orientation of the auroras.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Nitpicker » Sun Jun 22, 2014 11:41 pm

Chris Peterson wrote:
Marvin wrote:I don't wish to question the integrity of this picture - fascinating evolution of the aurorae. However, the 'Saturns' appear to be identical.
Good catch. The visible light image of Saturn was captured two months after the three UV images of the auroras. That single image of Saturn is simply being used as a template so that we can easily visualize the location and orientation of the auroras.
That's a bit cheeky. I'd like to think the UV images of the aurorae were taken two Saturn days -- or at least an integer multiple of Saturn days -- apart. (One Saturn day is approximately 10.5 Earth hours).

But then again, I don't even know if Saturn's aurorae rotate with the planet or not. I suspect they might not, or at least not as fast as the planet.

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by geckzilla » Mon Jun 23, 2014 12:48 am

A bit fun to look at the raw pictures for this one. http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Nitpicker » Mon Jun 23, 2014 1:06 am

geckzilla wrote:A bit fun to look at the raw pictures for this one. http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
Thanks geck. Very satisfying. From that, I would conclude that Saturn's aurorae do rotate with the planet. This would imply that the particles in Saturn's atmosphere continue to glow after the initial bursts from the solar wind subside. I suppose that makes perfect sense as the aurorae are lasting much longer than must the peak bursts of solar wind.

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by neufer » Mon Jun 23, 2014 1:40 am

Nitpicker wrote:
geckzilla wrote:
A bit fun to look at the raw pictures for this one. http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
Thanks geck. Very satisfying. From that, I would conclude that Saturn's aurorae do rotate with the planet. This would imply that the particles in Saturn's atmosphere continue to glow after the initial bursts from the solar wind subside. I suppose that makes perfect sense as the aurorae are lasting much longer than must the peak bursts of solar wind.
Or, perhaps, everything is simply rotating with the magnetic field.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Nitpicker » Mon Jun 23, 2014 1:59 am

neufer wrote:
Nitpicker wrote:
geckzilla wrote:
A bit fun to look at the raw pictures for this one. http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
Thanks geck. Very satisfying. From that, I would conclude that Saturn's aurorae do rotate with the planet. This would imply that the particles in Saturn's atmosphere continue to glow after the initial bursts from the solar wind subside. I suppose that makes perfect sense as the aurorae are lasting much longer than must the peak bursts of solar wind.
Or, perhaps, everything is simply rotating with the magnetic field.
Um, yes, I confess I didn't think things all the way through in this instance.

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Beyond » Mon Jun 23, 2014 2:07 am

geckzilla wrote:A bit fun to look at the raw pictures for this one. http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
Yes, it is a 'bit' of fun! Every time i click on the link, i get this-->


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I guess i must have a non-compatible IE. Either that, or they don't want to show me any uncooked (raw) pictures. :lol2:
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by geckzilla » Mon Jun 23, 2014 2:18 am

If you're using IE 11 you have to add stsci.edu to the compatibility view list.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Beyond » Mon Jun 23, 2014 3:14 am

geckzilla wrote:If you're using IE 11 you have to add stsci.edu to the compatibility view list.
Oh, thanx, i didn't know that. Now all i gotta do is find where the compatability list is in Windows 8.1.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Beyond » Mon Jun 23, 2014 3:21 am

Gee, no pictures. Just a lot of stuff i don't know anything about. Although "SEXCat" may be somewhat interesting.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Boomer12k » Mon Jun 23, 2014 6:09 am

Cool....

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by CharliePatriot » Mon Jun 23, 2014 1:47 pm

While not on subject, as a novice I am curious about the bands of color seen in Jupiter's atmosphere. I wonder how they can remain so distinct from each other without "blending". What keeps them confined to their line of orbit.?

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Mon Jun 23, 2014 2:29 pm

Beyond wrote:Gee, no pictures. Just a lot of stuff i don't know anything about. Although "SEXCat" may be somewhat interesting.
It's a list of images. You can click on the "Display" link to see a quick screen render, or the "TAR" link to download all the raw image components for that dataset (but you'll need software that can display or manipulate FITS files).

SEXCat refers to SExtractor, a tool that finds the positions of stars and extended objects in an image that can then be matched to a catalog in order to "solve the plate", meaning to very accurately relate an x-y position on the image to a right ascension-declination celestial coordinate. The blank entries mean that no SExtractor catalog is included with the dataset- not surprising since these images contain no star fields.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by occasional lurker » Mon Jun 23, 2014 2:45 pm

I find the addtional shadow detail of the 'overlapping saturns' very artistic! Hand-made gradients on the both the planet and the rings . .nice!

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Mon Jun 23, 2014 2:51 pm

occasional lurker wrote:I find the addtional shadow detail of the 'overlapping saturns' very artistic! Hand-made gradients on the both the planet and the rings . .nice!
It's a nice effect, but probably motivated by laziness as much as anything. It's a lot easier to overselect the source images and feather the edges than it is to very accurately select just the planet and ring edges. And doing the latter looks really bad unless you get things perfect.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by occasional lurker » Mon Jun 23, 2014 2:55 pm

whoops . . sorry about that typo, Chief! correction: additional

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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by neufer » Mon Jun 23, 2014 3:00 pm

CharliePatriot wrote:
While not on subject, as a novice I am curious about the bands of color seen in Jupiter's atmosphere. I wonder how they can remain so distinct from each other without "blending". What keeps them confined to their line of orbit.?
Saturn's rapid rotation produces strong opposing Coriolis forces around its equatorial regions which suppress any meridional motion away from its equatorial jet stream (or any other jet streams not sitting very near the poles themselves) . The so called Rossby parameter only gets sufficently weak very near the poles to allow for some very small amplitude Rossby waves:
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Beyond » Mon Jun 23, 2014 4:35 pm

Chris Peterson wrote:
Beyond wrote:Gee, no pictures. Just a lot of stuff i don't know anything about. Although "SEXCat" may be somewhat interesting.
It's a list of images. You can click on the "Display" link to see a quick screen render, or the "TAR" link to download all the raw image components for that dataset (but you'll need software that can display or manipulate FITS files).

SEXCat refers to SExtractor, a tool that finds the positions of stars and extended objects in an image that can then be matched to a catalog in order to "solve the plate", meaning to very accurately relate an x-y position on the image to a right ascension-declination celestial coordinate. The blank entries mean that no SExtractor catalog is included with the dataset- not surprising since these images contain no star fields.
So these images Hubble took, i take it, are about what we would see with our eyes IF we were just hanging out in space somewhere close to Saturn?
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Mon Jun 23, 2014 4:45 pm

Beyond wrote:So these images Hubble took, i take it, are about what we would see with our eyes IF we were just hanging out in space somewhere close to Saturn?
Not really. They're 5-10 minute exposures made in ultraviolet light. What we'd see if we were hanging out there in space would look like the processed image seen in the APOD, but without the aurora, which would be invisible to our eyes against the reflected light from the planet.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by geckzilla » Mon Jun 23, 2014 5:54 pm

Chris Peterson wrote:
occasional lurker wrote:I find the addtional shadow detail of the 'overlapping saturns' very artistic! Hand-made gradients on the both the planet and the rings . .nice!
It's a nice effect, but probably motivated by laziness as much as anything. It's a lot easier to overselect the source images and feather the edges than it is to very accurately select just the planet and ring edges. And doing the latter looks really bad unless you get things perfect.
:roll: Seriously, Chris? Saturn is one of the easiest selections to make (it's literally two ellipses) but with it on the black background and being the same Saturn three times, laziness is not a requirement here. This is just a very easy effect to achieve with Photoshop's tools.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Mon Jun 23, 2014 9:45 pm

geckzilla wrote:Seriously, Chris? Saturn is one of the easiest selections to make (it's literally two ellipses) but with it on the black background and being the same Saturn three times, laziness is not a requirement here. This is just a very easy effect to achieve with Photoshop's tools.
Yes, seriously (although that's not a criticism, since the easy way of doing this also results in a more aesthetically pleasing image).

Extracting a bright object with slightly fuzzy edges from a black background in such a way as to leave no border takes a bit of work. I recreated the composite, and I spent a good 15 minutes doing so. The same thing with feathered edges didn't even take 5 minutes.

It's interesting how we lose the rings against the planet without the feathered black region around each.
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by geckzilla » Mon Jun 23, 2014 10:29 pm

Yes, the shadow was not added because the background was difficult or time-consuming to drop out. This has got to be one of the easiest background dropouts I've ever seen... it took about two minutes start to finish using a vector shape to create an outline to pick Saturn up off the background.
http://www.geckzilla.com/astro/saturn_transparent.png

The shadow was added to add depth and aesthetics to the image as well as reducing the confusion by making each image of Saturn clearly separated. I would count Zolt as an expert with Photoshop, and he's an artist on top of that. I admire him quite a bit. ;)
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Re: APOD: Persistent Saturnian Auroras (2014 Jun 22)

Post by Chris Peterson » Mon Jun 23, 2014 11:07 pm

geckzilla wrote:Yes, the shadow was not added because the background was difficult or time-consuming to drop out. This has got to be one of the easiest background dropouts I've ever seen... it took about two minutes start to finish using a vector shape to create an outline to pick Saturn up off the background.
http://www.geckzilla.com/astro/saturn_transparent.png
Adequate for some purposes, but not very good. I know you can do a lot better. But not in two minutes. Your background cut took all the subtlety of the ring edge with it. All you have to do to see that is to lay your cutout on the original and blink them.
The shadow was added to add depth and aesthetics to the image as well as reducing the confusion by making each image of Saturn clearly separated. I would count Zolt as an expert with Photoshop, and he's an artist on top of that. I admire him quite a bit. ;)
I don't know the motives. Certainly, it looks better with the soft cut (which I would not call a shadow). It's a bonus that overselecting and feathering doesn't require any real effort, unlike making a good cutout.
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