APOD: Cassini Looks Out from Saturn (2022 Dec 23)

[APOD Robot]

Cassini Looks Out from Saturn

Explanation: This is what Saturn looks like from inside the rings. In 2017, for the first time, NASA directed the Cassini spacecraft to swoop between Saturn and its rings. During the dive, the robotic spacecraft took hundreds of images showing unprecedented detail for structures in Saturn's atmosphere. Looking back out, however, the spacecraft was also able to capture impressive vistas. In the featured image, taken a few hours before closest approach, Saturn's unusual northern hexagon is seen surrounding the North Pole. Saturn's B ring is the closest visible, while the dark Cassini Division separates B from the outer A. A close inspection will find the two small moons that shepherd the F-ring, the farthest ring discernable. A few months after this image was taken -- and after more than a decade of exploration and discovery -- the Cassini spacecraft ran low on fuel and was directed to enter Saturn's atmosphere, where it surely melted.

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[De58te]

Re the title, Cassini Looks Out From Saturn on 2022 DEC 23. I could have sworn that when Cassini plunged into Saturn's atmosphere in September 2017 that talk was that it couldn't survive and that it would burn up and be destroyed! Do you mean that Cassini actually survived and that it is functioning again today looking out from Saturn's clouds?

[Chris Peterson]

Re the title, Cassini Looks Out From Saturn on 2022 DEC 23. I could have sworn that when Cassini plunged into Saturn's atmosphere in September 2017 that talk was that it couldn't survive and that it would burn up and be destroyed! Do you mean that Cassini actually survived and that it is functioning again today looking out from Saturn's clouds?

But... that isn't the title. Not of the APOD, not of the discussion.

[orin stepanek]

what causes the hexagon shape at the N. Pole?

cat-with-book-1.jpg (9.53 KiB) Viewed 4225 times

kitty searching book!

Puppy taking a nap!

[Chris Peterson]

what causes the hexagon shape at the N. Pole?

https://en.wikipedia.org/wiki/Saturn%27 ... agon_shape

[orin stepanek]

Thanks Chris; I'll let that soak in;

[johnnydeep]

I couldn't find the two shepherd moons of the outermost F ring in this image as is (even under "close inspection"), but inverting the colors clearly made them stand out:

[Bird_Man]

Thank you Johnnydeep. When I came to this discussion thread I said "I know someone smart will show me the moons. And you did. I tried the same inverting the image colors as you did and now I can find the moons. Great tip, thanks.

[johnnydeep]

Thank you Johnnydeep. When I came to this discussion thread I said "I know someone smart will show me the moons. And you did. I tried the same inverting the image colors as you did and now I can find the moons. Great tip, thanks.

[johnnydeep]

Thank you Johnnydeep. When I came to this discussion thread I said "I know someone smart will show me the moons. And you did. I tried the same inverting the image colors as you did and now I can find the moons. Great tip, thanks.

Just one more comment: this makes me wonder why humans seem to be so much better at discerning small dark things against a light background than they are at discerning small light things against a dark background (which is the "natural" way that a typical photo of space appears). Why is this true?

[MarkBour]

Thank you Johnnydeep. When I came to this discussion thread I said "I know someone smart will show me the moons. And you did. I tried the same inverting the image colors as you did and now I can find the moons. Great tip, thanks.

Just one more comment: this makes me wonder why humans seem to be so much better at discerning small dark things against a light background than they are at discerning small light things against a dark background (which is the "natural" way that a typical photo of space appears). Why is this true?

Me too, I came to the discussion, hoping someone would help. Bingo! Thanks johnny.

As to the question you've now put, I think it may have something to do with context. I'd like to find some experiment that carefully tried to answer your question -- "Are humans better at seeing a small speck of light in the dark, or a small speck of dark in the light?" But the situation we're discussing here, when I look at my computer monitor is:

Code: Select all

---------------------------------------------------------
|     Lots of light                                     |
|                                                       |
|           ---------------------------------           |
|           |  a region of dark, with two   |           |
|           |  very small specks of         |           |
|           |  light, and then nearby,      |           |
|           |  brighter regions of light    |           |
|           ---------------------------------           |
---------------------------------------------------------

I'm just saying, this image may be complicated. Usually, when I'm on a computer, I'm in a lighted room. And sure enough, a light speck on a dark background is hard to see. What about if I've been sitting in a totally darkened room for a while and a tiny speck of light is turned on? Anyway, it still may be quite true, what you said, "better at discerning small dark things against a light background than they are at discerning small light things against a dark background", but it might depend on context.

Here's an article that doesn't really settle it scientifically, but it and the comments give lots of perspectives:
https://tidbits.com/2019/05/31/the-dark ... dark-mode/

I could not find any scholarly reference that dealt with this issue. Admittedly, I did not spend much time at it.

[johnnydeep]

Thank you Johnnydeep. When I came to this discussion thread I said "I know someone smart will show me the moons. And you did. I tried the same inverting the image colors as you did and now I can find the moons. Great tip, thanks.

Just one more comment: this makes me wonder why humans seem to be so much better at discerning small dark things against a light background than they are at discerning small light things against a dark background (which is the "natural" way that a typical photo of space appears). Why is this true?

Me too, I came to the discussion, hoping someone would help. Bingo! Thanks johnny.

As to the question you've now put, I think it may have something to do with context. I'd like to find some experiment that carefully tried to answer your question -- "Are humans better at seeing a small speck of light in the dark, or a small speck of dark in the light?" But the situation we're discussing here, when I look at my computer monitor is:

Code: Select all

---------------------------------------------------------
|     Lots of light                                     |
|                                                       |
|           ---------------------------------           |
|           |  a region of dark, with two   |           |
|           |  very small specks of         |           |
|           |  light, and then nearby,      |           |
|           |  brighter regions of light    |           |
|           ---------------------------------           |
---------------------------------------------------------

I'm just saying, this image may be complicated. Usually, when I'm on a computer, I'm in a lighted room. And sure enough, a light speck on a dark background is hard to see. What about if I've been sitting in a totally darkened room for a while and a tiny speck of light is turned on? Anyway, it still may be quite true, what you said, "better at discerning small dark things against a light background than they are at discerning small light things against a dark background", but it might depend on context.

Here's an article that doesn't really settle it scientifically, but it and the comments give lots of perspectives:
https://tidbits.com/2019/05/31/the-dark ... dark-mode/

I could not find any scholarly reference that dealt with this issue. Admittedly, I did not spend much time at it.

I had a revelation last night that may actually be valid. Could it be that the reason humans can better discern dark things on light backgrounds than the reverse (assuming that this is in fact the case) is that it was an evolutionary advantage to be able to do so? The daytime lives of our hominid ancestors mainly involved hunting for or gathering food, and evading predators. So, being able to see a dark fish in the shallows against a light sandy bottom, or a vulture or raptor against a pale blue sky, or an animal - be it predator or prey - silhouetted against a tawny desert landscape would surely be beneficial to survival. Whereas being able to see stars in the sky, though perhaps giving rise to awe and wonder, was not a survival advantage?

[MarkBour]

I had a revelation last night that may actually be valid. Could it be that the reason humans can better discern dark things on light backgrounds than the reverse (assuming that this is in fact the case) is that it was an evolutionary advantage to be able to do so? The daytime lives of our hominid ancestors mainly involved hunting for or gathering food, and evading predators. So, being able to see a dark fish in the shallows against a light sandy bottom, or a vulture or raptor against a pale blue sky, or an animal - be it predator or prey - silhouetted against a tawny desert landscape would surely be beneficial to survival. Whereas being able to see stars in the sky, though perhaps giving rise to awe and wonder, was not a survival advantage?

Yes, I think that makes perfect sense.

As you're saying, I think we tend to use a light background and look for and focus on bits of darkness for information. And you have a very plausible reason that led to this becoming the case. Nocturnal animals might be intermediate. Perhaps some deep-sea fish have evolved in a way that was truly opposite and can better see specks of light than the reverse.

[johnnydeep]

I had a revelation last night that may actually be valid. Could it be that the reason humans can better discern dark things on light backgrounds than the reverse (assuming that this is in fact the case) is that it was an evolutionary advantage to be able to do so? The daytime lives of our hominid ancestors mainly involved hunting for or gathering food, and evading predators. So, being able to see a dark fish in the shallows against a light sandy bottom, or a vulture or raptor against a pale blue sky, or an animal - be it predator or prey - silhouetted against a tawny desert landscape would surely be beneficial to survival. Whereas being able to see stars in the sky, though perhaps giving rise to awe and wonder, was not a survival advantage?

Yes, I think that makes perfect sense.

As you're saying, I think we tend to use a light background and look for and focus on bits of darkness for information. And you have a very plausible reason that led to this becoming the case. Nocturnal animals might be intermediate. Perhaps some deep-sea fish have evolved in a way that was truly opposite and can better see specks of light than the reverse.

Yes, especially very deep down where there is perpetual darkness and animals rely on bioluminescence to see and be seen. Perhaps such creatures would make ideal astronomers!

Now the question is: did our eyes themselves evolve structure to better process dark things on light backgrounds, or was it mainly neural and brain processing that evolved. I guess probably a combination of both, which makes me wonder if a human can better train their brain to discern light things on dark backgrounds - in ways better than just acclimating their eyes to an absence of light.