APOD: Rosetta's Selfie (2014 Oct 16)

Comments and questions about the APOD on the main view screen.
sOnIc
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by sOnIc » Sat Oct 18, 2014 7:02 pm

Chris Peterson wrote:It's hard to say for certain without the exposure details of the individual images, but I wouldn't be surprised if we could comfortably see the panels and the dust jets in the same view.
Ok, how cool would that be! And that was my initial reaction .. just upon reading the caption it makes me uncertain about that point, as you are.
Thanks for your opinions and info Chris, I was just posting my thoughts ...

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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by geckzilla » Sat Oct 18, 2014 7:54 pm

If you were able to float out there and use either the craft or the comet itself to hide the Sun and let your eyes adjust, you could probably see all sorts of fine details. Getting on the backside of the comet would probably let you see even more detail from the jets. I'm under the impression the jets with the sunlight reflecting off them are much brighter than, say, an emission nebula like Orion until they diffuse away from the comet.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by alter-ego » Sat Oct 18, 2014 9:30 pm

Chris Peterson wrote:
sOnIc wrote:For example if you were onboard the spacecraft you could shield you eyes and dark adapt your vision for a while; then look back at the comet and maybe see the dust; like seeing the milky way in the night sky.
Actually, this image may be doing a good job of capturing what you'd see with your naked eyes. Our visual dynamic range is many orders of magnitude greater than we can capture in any single image. That's one reason for HDR: it results in images that come closer to what we actually see. It's hard to say for certain without the exposure details of the individual images, but I wouldn't be surprised if we could comfortably see the panels and the dust jets in the same view.
My immediate thoughts were that if one were at CIVA's location, a naked eye view would comfortably show the fainter information, but that it might include shielding our eyes from the brightest sources (the saturated glints from the array panels). Interestingly, I ran across some exposure details at http://blogs.esa.int/rosetta/2014/09/10 ... -at-comet/
Selfie Exposure Details.JPG
The full dynamic range of the composite ≈12000, or ≈13.5 f-stops. Given the eye has a static contrast ratio of about 6.5 f-stops (fixed brightness range), the image well exceeds that. However, it is well within the eye's full dynamic contrast ratio of 20 f-stops. I'd estimate the jet is near the faint range (maybe 10 to 13 f-stops), so the visibility would likely depend on blocking the brightest regions (certainly true for the fainter jet regions).

Edit: I just realized that the selfie posted on the blog site is from Sep 7 (no jet and array panels positioned differently wrt the comet, 50km away). I'm therefore assuming the exposure information also applies to the Oct 7 selfie in the APOD.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by Chris Peterson » Sun Oct 19, 2014 4:24 am

alter-ego wrote:The full dynamic range of the composite ≈12000, or ≈13.5 f-stops. Given the eye has a static contrast ratio of about 6.5 f-stops (fixed brightness range), the image well exceeds that. However, it is well within the eye's full dynamic contrast ratio of 20 f-stops. I'd estimate the jet is near the faint range (maybe 10 to 13 f-stops), so the visibility would likely depend on blocking the brightest regions (certainly true for the fainter jet regions).
It probably would not be necessary to look away or shield the eyes. The static contrast ratio of the eyes only applies when you're fixated on something. In practice we move our eyes, and our brain paints the whole picture. So in normal operation we get better than 90dB of dynamic range (for daylight illumination levels), about three times deeper than the image.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by alter-ego » Sun Oct 19, 2014 4:50 am

Chris Peterson wrote:
alter-ego wrote:The full dynamic range of the composite ≈12000, or ≈13.5 f-stops. Given the eye has a static contrast ratio of about 6.5 f-stops (fixed brightness range), the image well exceeds that. However, it is well within the eye's full dynamic contrast ratio of 20 f-stops. I'd estimate the jet is near the faint range (maybe 10 to 13 f-stops), so the visibility would likely depend on blocking the brightest regions (certainly true for the fainter jet regions).
It probably would not be necessary to look away or shield the eyes. The static contrast ratio of the eyes only applies when you're fixated on something. In practice we move our eyes, and our brain paints the whole picture. So in normal operation we get better than 90dB of dynamic range (for daylight illumination levels), about three times deeper than the image.
That makes sense. I'd think that depending the brightness of the surrounding sources (array glints and comet sun-lit contributions), that eye motion would be intentional and relatively large compared to the normal (rapid) eye saccades that one experiences while attempting to fixate on a point. There is a source brightness limit, within the image FoV, beyond which the jet would not be visible regardless, but I'd say nothing in the image is near that limit.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by Chris Peterson » Sun Oct 19, 2014 4:54 am

alter-ego wrote:I'd think that depending the brightness of the surrounding sources (array glints and comet sun-lit contributions), that eye motion would be intentional and relatively large compared to the normal (rapid) eye saccades that one experiences while attempting to fixate on a point.
Right, I'm talking about large movements. We actually only see clearly in a tiny region in the center of our gaze. But we never notice unless we really try. We scan our eyes (and even head) over a very wide field, and our brain just paints it all in, as if our eyes were taking it all in at once. Kind of a neat trick.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by alter-ego » Sun Oct 19, 2014 5:09 am

Chris Peterson wrote:
alter-ego wrote:I'd think that depending the brightness of the surrounding sources (array glints and comet sun-lit contributions), that eye motion would be intentional and relatively large compared to the normal (rapid) eye saccades that one experiences while attempting to fixate on a point.
Right, I'm talking about large movements. We actually only see clearly in a tiny region in the center of our gaze. But we never notice unless we really try. We scan our eyes (and even head) over a very wide field, and our brain just paints it all in, as if our eyes were taking it all in at once. Kind of a neat trick.
Absolutely. It's funny though, that process seems to have always been second nature to me. I've been conducting my personal threshold magnitudes measurements from my home. The observations range from daytime to the nighttime limit. The transition from photopic to scotopic vision is an interesting phase. It is possible that seeing that jet might fall near this transition.
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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by sOnIc » Mon Oct 20, 2014 5:08 pm

Thanks for the link and info alter-ago .. just gives more understanding of the scene for me .. exciting mission . . .

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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by 50bmg » Fri Oct 24, 2014 3:54 pm

50bmg wrote:What are the spots on the solar panel? Perhaps micrometeoroid impacts?

Does anyone know anything about the spots on the solar panel? Thanks!

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Re: APOD: Rosetta's Selfie (2014 Oct 16)

Post by geckzilla » Fri Oct 24, 2014 4:51 pm

50bmg wrote:
50bmg wrote:What are the spots on the solar panel? Perhaps micrometeoroid impacts?
Does anyone know anything about the spots on the solar panel? Thanks!
I know that this is the back of Rosetta's solar cells. The disorganized nature of the white dots can lead one to believe they are randomly punched holes from space debris but check out this 3d rendering of Rosetta:
http://www.esa.int/spaceinimages/Images/2013/12/Rosetta

You can see there are seemingly random white dots on the front of the cells. However, they're actually very regularly placed and clearly correspond to the white dots seen on the back of the solar panels in the APOD image. That doesn't mean there are no impact holes in Rosetta. It just means most of these spots probably are not.
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