APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Comments and questions about the APOD on the main view screen.
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by BillT » Sun Jul 10, 2022 11:13 pm

Doesn't require any experience. Everyone I have shown these two can see the the colour without any prompting. Even people who have never looked through a scope in their life before.

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Sun Jul 10, 2022 11:25 pm

BillT wrote: Sun Jul 10, 2022 11:13 pm Doesn't require any experience. Everyone I have shown these two can see the the colour without any prompting. Even people who have never looked through a scope in their life before.
I don't know who you have shown, but very few people can see color in any deep sky objects.
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Fred the Cat » Mon Jul 11, 2022 1:58 am

A person could present the "Cat's Eye" in any medium and enjoy it but many may not think it representative.
IMG_8636.JPG
The creativity that inspired it, is left for the eye of the beholder. :wink:
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Mon Jul 11, 2022 4:17 am

Chris Peterson wrote: Sun Jul 10, 2022 10:32 pm
Ann wrote: Sun Jul 10, 2022 10:03 pm
Chris Peterson wrote: Sun Jul 10, 2022 9:47 pm

Easy. They are all gray. ;-)
Well, Chris, the day you have convinced me that all astronomical objects are gray, I'm outta here.

Seriously.

Ann
Just ask anybody who has ever observed deep sky objects directly.
Certainly, Chris.

Do I take it that you think that all astroimages should show only what the human eye can observe directly through a telescope?

Consider the APOD of July 11, 2022, and compare it with what a direct observation of the same object might look like:

Andromeda widefield tavaresjr.png
Wide field Andromeda. Image: tavaresjr.

Is it fair to show as much detail in Andromeda as we can see in today's APOD? When direct observation through a telescope may not reveal much more than what can be seen in tavaresjr's image?

Ann
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Mon Jul 11, 2022 4:40 am

Ann wrote: Mon Jul 11, 2022 4:17 am
Chris Peterson wrote: Sun Jul 10, 2022 10:32 pm
Ann wrote: Sun Jul 10, 2022 10:03 pm

Well, Chris, the day you have convinced me that all astronomical objects are gray, I'm outta here.

Seriously.

Ann
Just ask anybody who has ever observed deep sky objects directly.
Certainly, Chris.

Do I take it that you think that all astroimages should show only what the human eye can observe directly through a telescope?
No. But color loses most of its meaning when you are talking about things that the eye cannot perceive. Color is physiology, not physics.
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Mon Jul 11, 2022 5:47 am

Chris Peterson wrote: Mon Jul 11, 2022 4:40 am
Ann wrote: Mon Jul 11, 2022 4:17 am
Chris Peterson wrote: Sun Jul 10, 2022 10:32 pm
Just ask anybody who has ever observed deep sky objects directly.
Certainly, Chris.

Do I take it that you think that all astroimages should show only what the human eye can observe directly through a telescope?
No. But color loses most of its meaning when you are talking about things that the eye cannot perceive. Color is physiology, not physics.
But wavelengths are physics. Relative wavelengths are physics, too.

In both Spitzer Space Telescope infrared images and GALEX ultraviolet images, shorter wavelengths were mapped as blue or cyan, and longer wavelengths were mapped as red or yellow. This makes perfect sense to me.


In SDSS g-r-i images of galaxies, green wavelengths are mapped as blue, red wavelengths are mapped as green and infrared wavelengths are mapped as red. Again shorter wavelengths are mapped as bluer hues and longer wavelengths are redder hues. Again, this makes perfect sense to me (and it has the consequence that red emission nebulas look green or cyan-colored in SDSS images, while individual cool stars tend to look very red).

But why does the Saturn Nebula look like that in a Hubble image? It makes no sense to me.

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Mon Jul 11, 2022 12:03 pm

Ann wrote: Mon Jul 11, 2022 5:47 am
Chris Peterson wrote: Mon Jul 11, 2022 4:40 am
Ann wrote: Mon Jul 11, 2022 4:17 am Certainly, Chris.

Do I take it that you think that all astroimages should show only what the human eye can observe directly through a telescope?
No. But color loses most of its meaning when you are talking about things that the eye cannot perceive. Color is physiology, not physics.
But wavelengths are physics. Relative wavelengths are physics, too.
Relative wavelengths are particularly irrelevant when we're considering narrow band images.

But why does the Saturn Nebula look like that in a Hubble image? It makes no sense to me.
I don't know why it makes no sense to you. Is it confusing that you say hej då and I say goodbye? Different sounds with the same meaning. Why is translating wavelengths to colors any different?
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Mon Jul 11, 2022 1:42 pm

Chris Peterson wrote: Mon Jul 11, 2022 12:03 pm
Ann wrote: Mon Jul 11, 2022 5:47 am
Chris Peterson wrote: Mon Jul 11, 2022 4:40 am

No. But color loses most of its meaning when you are talking about things that the eye cannot perceive. Color is physiology, not physics.
But wavelengths are physics. Relative wavelengths are physics, too.
Relative wavelengths are particularly irrelevant when we're considering narrow band images.

But why does the Saturn Nebula look like that in a Hubble image? It makes no sense to me.
I don't know why it makes no sense to you. Is it confusing that you say hej då and I say goodbye? Different sounds with the same meaning. Why is translating wavelengths to colors any different?
Perhaps we should say hej då and goodbye to this discussion, Chris?

You and I view color in the Universe in a fundamentally different way. To me color in astronomical objects is certainly a very subjective thing and a source of great joy, but it is also precise physical parameter. In the latter case, we are talking wavelengths, of course, not the conversion by the human eye and brain into the subjective sensation that we call color.

To me, color is hugely important, both when it comes to my own sense of aesthetics and when it comes to understanding the fundamental properties of an object through the wavelengths emitted or reflected by the object in question. To me, the color (or wavelength) of an astronomical object is no more trivial than the size, mass or shape of the object.

I'm sure you know that. And you don't agree with me. So let's agree to disagree. I'll keep claiming that an APOD portrait of an object gives us a good, or a misleading, idea of what the object's "natural", or optical, or visual, color is. And you are going to tell everyone here that I'm talking nonsense.

That's okay. You and I disagree on color. Let's leave it at that and say hej då and goodbye, until there is another APOD whose "color portrait" of an object prompts me to explain the properties of the object from its ("true") color.

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Tue Jul 12, 2022 1:54 pm

Ann wrote: Mon Jul 11, 2022 1:42 pm
Chris Peterson wrote: Mon Jul 11, 2022 12:03 pm
Ann wrote: Mon Jul 11, 2022 5:47 am

But wavelengths are physics. Relative wavelengths are physics, too.
Relative wavelengths are particularly irrelevant when we're considering narrow band images.

But why does the Saturn Nebula look like that in a Hubble image? It makes no sense to me.
I don't know why it makes no sense to you. Is it confusing that you say hej då and I say goodbye? Different sounds with the same meaning. Why is translating wavelengths to colors any different?
Perhaps we should say hej då and goodbye to this discussion, Chris?

You and I view color in the Universe in a fundamentally different way. To me color in astronomical objects is certainly a very subjective thing and a source of great joy, but it is also precise physical parameter. In the latter case, we are talking wavelengths, of course, not the conversion by the human eye and brain into the subjective sensation that we call color.

To me, color is hugely important, both when it comes to my own sense of aesthetics and when it comes to understanding the fundamental properties of an object through the wavelengths emitted or reflected by the object in question. To me, the color (or wavelength) of an astronomical object is no more trivial than the size, mass or shape of the object.

I'm sure you know that. And you don't agree with me. So let's agree to disagree. I'll keep claiming that an APOD portrait of an object gives us a good, or a misleading, idea of what the object's "natural", or optical, or visual, color is. And you are going to tell everyone here that I'm talking nonsense.

That's okay. You and I disagree on color. Let's leave it at that and say hej då and goodbye, until there is another APOD whose "color portrait" of an object prompts me to explain the properties of the object from its ("true") color.

Ann
I don't disagree with that much. But I will not agree to agree with you calling any color scheme "wrong". Because that is wrong, and I'll call you out every time!
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Tue Jul 12, 2022 5:20 pm

Chris Peterson wrote: Tue Jul 12, 2022 1:54 pm
I don't disagree with that much. But I will not agree to agree with you calling any color scheme "wrong". Because that is wrong, and I'll call you out every time!
Do that, Chris, because the word "wrong" is particularly useless as a description of color in astronomical objects. The adjective is provocative and annoying, but practically devoid of all precise information.

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Tue Jul 12, 2022 6:06 pm

Ann wrote: Tue Jul 12, 2022 5:20 pm
Chris Peterson wrote: Tue Jul 12, 2022 1:54 pm
I don't disagree with that much. But I will not agree to agree with you calling any color scheme "wrong". Because that is wrong, and I'll call you out every time!
Do that, Chris, because the word "wrong" is particularly useless as a description of color in astronomical objects. The adjective is provocative and annoying, but practically devoid of all precise information.

Ann
Well, speaking of color, I'm sure you'll appreciate this, taken at 3700 meters on a hike yesterday. Chiming Bells and Columbine. There were blue wildflowers everywhere. Nothing wrong about these colors!
_
PXL_20220712_011055280p.jpg
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by VictorBorun » Tue Jul 12, 2022 6:11 pm

Ann wrote: Mon Jul 11, 2022 5:47 am But wavelengths are physics. Relative wavelengths are physics, too.
In both Spitzer Space Telescope infrared images and GALEX ultraviolet images, shorter wavelengths were mapped as blue or cyan, and longer wavelengths were mapped as red or yellow. This makes perfect sense to me.
In SDSS g-r-i images of galaxies, green wavelengths are mapped as blue, red wavelengths are mapped as green and infrared wavelengths are mapped as red. Again shorter wavelengths are mapped as bluer hues and longer wavelengths are redder hues. Again, this makes perfect sense to me (and it has the consequence that red emission nebulas look green or cyan-colored in SDSS images, while individual cool stars tend to look very red).

But why does the Saturn Nebula look like that in a Hubble image? It makes no sense to me.
Ann
Here come new images from Webb, with its wild wide band, far IR having 10 times lower resolution than near IR.
To fully use human vision, we should encode the longest waves in blue sub-pixels of an RGB picture.
To preserve the monotony even if takes to inverse it we should encode the shortest waves in red.
It would take time to get used to that legend where hot is red and cold is blue (and halfway warm-cool is not gray, but rather green), but what other way is there?

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Tue Jul 12, 2022 6:24 pm

Chris Peterson wrote: Tue Jul 12, 2022 6:06 pm
Ann wrote: Tue Jul 12, 2022 5:20 pm
Chris Peterson wrote: Tue Jul 12, 2022 1:54 pm
I don't disagree with that much. But I will not agree to agree with you calling any color scheme "wrong". Because that is wrong, and I'll call you out every time!
Do that, Chris, because the word "wrong" is particularly useless as a description of color in astronomical objects. The adjective is provocative and annoying, but practically devoid of all precise information.

Ann
Well, speaking of color, I'm sure you'll appreciate this, taken at 3700 meters on a hike yesterday. Chiming Bells and Columbine. There were blue wildflowers everywhere. Nothing wrong about these colors!
_
Thanks, Chris, they are lovely! :D 💙💜💙

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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Chris Peterson » Tue Jul 12, 2022 6:26 pm

VictorBorun wrote: Tue Jul 12, 2022 6:11 pm To preserve the monotony even if takes to inverse it we should encode the shortest waves in red.
Monotonicity, please! Monotony is very different, and not to be found in the JWST images. :lol2:
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by Ann » Tue Jul 12, 2022 6:34 pm

Got to show you perhaps the most beautiful picture I have seen, fittingly called "The Blue Universe" by Japanese photographer Hiroki Kondo:

A blue universe in Japan Hiroki Kondo.png

Amazing, isn't it?
National Geographic wrote:
THE BLUE UNIVERSE

About 4.5 million Nemophila menziesii—a California wildflower commonly known as baby blue eyes—carpet the hills at Hitachi Seaside Park in Japan. According to photographer Hiroki Kondo, who calls this landscape “the blue universe,” the flowers peak from the end of April to the first week of May.
Amazing, isn't it? Sigh! Sometimes we can see heaven on Earth. Or - wait! I take that back! Sometimes we can really see that the Earth is the heaven of the Universe. At the very least, it sure looks like it sometimes!

Ann
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by johnnydeep » Tue Jul 12, 2022 6:38 pm

Ann wrote: Tue Jul 12, 2022 6:34 pm Got to show you perhaps the most beautiful picture I have seen, fittingly called "The Blue Universe" by Japanese photographer Hiroki Kondo:

A blue universe in Japan Hiroki Kondo.png

Amazing, isn't it?
National Geographic wrote:
THE BLUE UNIVERSE

About 4.5 million Nemophila menziesii—a California wildflower commonly known as baby blue eyes—carpet the hills at Hitachi Seaside Park in Japan. According to photographer Hiroki Kondo, who calls this landscape “the blue universe,” the flowers peak from the end of April to the first week of May.
Amazing, isn't it? Sigh! Sometimes we can see heaven on Earth. Or - wait! I take that back! Sometimes we can really see that the Earth is the heaven of the Universe. At the very least, it sure looks like it sometimes!

Ann
Nice. All that's missing is a stretch of nice blue ocean between earth and sea!
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Re: APOD: In the Center of the Cat's Eye Nebula (2022 Jul 10)

Post by MarkBour » Wed Jul 13, 2022 6:26 pm

Ann wrote: Tue Jul 12, 2022 6:34 pm Got to show you perhaps the most beautiful picture I have seen, fittingly called "The Blue Universe" by Japanese photographer Hiroki Kondo:
...
Amazing, isn't it? Sigh! Sometimes we can see heaven on Earth. Or - wait! I take that back! Sometimes we can really see that the Earth is the heaven of the Universe. At the very least, it sure looks like it sometimes!

Ann
Nice! I especially like the color in the shade of the tree.
It is nice of the Japanese to allow these Californians to flourish.
Mark Goldfain