APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

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APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by APOD Robot » Sun Aug 21, 2022 4:05 am

Image The Spinning Pulsar of the Crab Nebula

Explanation: At the core of the Crab Nebula lies a city-sized, magnetized neutron star spinning 30 times a second. Known as the Crab Pulsar, it is the bright spot in the center of the gaseous swirl at the nebula's core. About twelve light-years across, the spectacular picture frames the glowing gas, cavities and swirling filaments near the Crab Nebula's center. The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red. Like a cosmic dynamo the Crab pulsar powers the emission from the nebula, driving a shock wave through surrounding material and accelerating the spiraling electrons. With more mass than the Sun and the density of an atomic nucleus,the spinning pulsar is the collapsed core of a massive star that exploded. The outer parts of the Crab Nebula are the expanding remnants of the star's component gasses. The supernova explosion was witnessed on planet Earth in the year 1054.

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by JohnD » Sun Aug 21, 2022 9:58 am

Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Ann » Sun Aug 21, 2022 11:45 am

JohnD wrote: Sun Aug 21, 2022 9:58 am Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!
I agree with you! I can't see any red in this APOD either.

But since whatever red is supposed to be there is from an infrared Spitzer image, I googled "Crab Nebula Spitzer Space Telescope" and found this:


So there you are. What looks green in the image I posted should look red in today's APOD. I don't think I can see that shape in red. No problem, though, because the Spitzer Crab Nebula image doesn't look too impressive. It will look better when imaged by JWST, I'll wager.

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by smitty » Sun Aug 21, 2022 12:15 pm

Yes, to all those puzzled by the color business, me too. Among the most interesting features is the "tail," which looks white in the image I'm viewing.

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by AVAO » Sun Aug 21, 2022 1:55 pm

JohnD wrote: Sun Aug 21, 2022 9:58 am Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!
...here is a link in the APOD text to the original source...
"A new composite of the Crab Nebula with Chandra (blue and white), Hubble (purple), and Spitzer (pink) data has been released."
https://chandra.harvard.edu/photo/2018/crab/

The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue AND WHITE, and infrared light from the Spitzer Space Telescope in PINK.

Maybe this could be corrected in the APOD text...

I like this two animations:
https://www.youtube.com/watch?v=_KCCKl9SB90
https://www.youtube.com/watch?v=H9DN3ODUY-4

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Chris Peterson » Sun Aug 21, 2022 2:37 pm

JohnD wrote: Sun Aug 21, 2022 9:58 am Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!
This is why science doesn't use color images. They may be useful in seeing structure, but are very limited in showing anything else. Our eyes are not spectroscopes. "Purple" is red and blue. We have no way of telling if a pixel is purple because it represents visible light, or if it's purple because it represents a a mix of x-ray and IR. When you create a color image, you lose information.

All color pictures like this should be substantially treated as aesthetic, not scientific.

(Given that there are only three input channels, I would have mapped them to the display primaries of red, green, and blue. This would have resulted in less information loss.)
Chris

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by orin stepanek » Sun Aug 21, 2022 2:52 pm

multiWcrab_lg1024c.jpg
Aw; at least the color gives the photo beauty! The crab makes an
awesome photo!Pulsars are very scary; I'm glad they are so far away!
1000_F_343879856_Ino0o68y6MO3wCJsvVdclbT381NkKvhT.jpg
There's that pretty cat again! She looks so amazed at what she sees!
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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Ann » Sun Aug 21, 2022 5:08 pm

Chris Peterson wrote: Sun Aug 21, 2022 2:37 pm
JohnD wrote: Sun Aug 21, 2022 9:58 am Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!
This is why science doesn't use color images. They may be useful in seeing structure, but are very limited in showing anything else. Our eyes are not spectroscopes. "Purple" is red and blue. We have no way of telling if a pixel is purple because it represents visible light, or if it's purple because it represents a a mix of x-ray and IR. When you create a color image, you lose information.

All color pictures like this should be substantially treated as aesthetic, not scientific.

(Given that there are only three input channels, I would have mapped them to the display primaries of red, green, and blue. This would have resulted in less information loss.)
Since X-rays and infrared light don't represent visible colors in the first place, I would have had no problems with a black and white image here. That is particularly true since I don't regard the Crab Nebula as intrinsically blue in any way, so I wouldn't feel that a b/w image of the Crab would have robbed us of any "natural" blue light. (A strangely mapped and non-blue color image of, say, the Pleiades or the Trapezium in the Orion Nebula, now that's another matter!) :evil:

However, I actually think that a mapped color image of the Crab might have been more informative than a b/w one, assuming X-rays had been mapped as blue, visible light as green and infrared light as red. For clarity, we could have been shown the individual images (X-ray, optical, infrared) too. And these single filter images might well have been shown in black and white, as far as I'm concerned.

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Chris Peterson » Sun Aug 21, 2022 5:14 pm

Ann wrote: Sun Aug 21, 2022 5:08 pm
Chris Peterson wrote: Sun Aug 21, 2022 2:37 pm
JohnD wrote: Sun Aug 21, 2022 9:58 am Again, have I discovered, and am suffering from, an acquirable form of colour blindness?

Quote blurb, " The featured picture combines visible light from the Hubble Space Telescope in purple, X-ray light from the Chandra X-ray Observatory in blue, and infrared light from the Spitzer Space Telescope in red"
I see purple, blue and white. No red. I know, white light is all wavelengths at once, but when the white dominates the picture, that sentence is unhelpful!
This is why science doesn't use color images. They may be useful in seeing structure, but are very limited in showing anything else. Our eyes are not spectroscopes. "Purple" is red and blue. We have no way of telling if a pixel is purple because it represents visible light, or if it's purple because it represents a a mix of x-ray and IR. When you create a color image, you lose information.

All color pictures like this should be substantially treated as aesthetic, not scientific.

(Given that there are only three input channels, I would have mapped them to the display primaries of red, green, and blue. This would have resulted in less information loss.)
Since X-rays and infrared light don't represent visible colors in the first place, I would have had no problems with a black and white image here. That is particularly true since I don't regard the Crab Nebula as intrinsically blue in any way, so I wouldn't feel that a b/w image of the Crab would have robbed us of any "natural" blue light. (A strangely mapped and non-blue color image of, say, the Pleiades or the Trapezium in the Orion Nebula, now that's another matter!) :evil:

However, I actually think that a mapped color image of the Crab might have been more informative than a b/w one, assuming X-rays had been mapped as blue, visible light as green and infrared light as red. For clarity, we could have been shown the individual images (X-ray, optical, infrared) too. And these single filter images might well have been shown in black and white, as far as I'm concerned.
A B&W image constructed out of multiple input channels throws away even more information than a color one. Even a single channel represented in B&W is usually harder to interpret than the same image mapped to a pseudocolor palette. We can see more in today's image as presented than we would in B&W.

The choice of what colors to map input channels to should be made according to which preserves the most information, not according to the actual wavelengths. We can't ignore physiology and color perception.
Chris

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by De58te » Sun Aug 21, 2022 5:17 pm

I can see 3 colors besides the white. The blue is obvious. What they call purple I would think is the color that looks more precisely like lavender. And the red looks more like a burgundy color. Am I wrong?

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Chris Peterson » Sun Aug 21, 2022 5:19 pm

De58te wrote: Sun Aug 21, 2022 5:17 pm I can see 3 colors besides the white. The blue is obvious. What they call purple I would think is the color that looks more precisely like lavender. And the red looks more like a burgundy color. Am I wrong?
I can see hundreds of colors. Interpreting them is the problem.

Just because IR is mapped to red doesn't mean you'll see any red in the image!
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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by bystander » Sun Aug 21, 2022 6:05 pm

The featured picture can be seen at the Chandra site along with each of the component images, x-ray, optical, and infrared in the assigned colors.
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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by AVAO » Sun Aug 21, 2022 6:11 pm

Chris Peterson wrote: Sun Aug 21, 2022 5:19 pm
De58te wrote: Sun Aug 21, 2022 5:17 pm I can see 3 colors besides the white. The blue is obvious. What they call purple I would think is the color that looks more precisely like lavender. And the red looks more like a burgundy color. Am I wrong?
I can see hundreds of colors. Interpreting them is the problem.

Just because IR is mapped to red doesn't mean you'll see any red in the image!
ThanX Chris & Ann for this exceptionally interesting discussion.

The following image shows the APOD in RGB without any adjustments.
Image

Here you can see the close up of the central area.
Image

...Of course, they wanted to highlight the pulsar stream in the center of the APOD image. But I absolutly do not understand why people are willing to "lose" all the details...

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by bls0326 » Sun Aug 21, 2022 7:41 pm

De58te wrote: Sun Aug 21, 2022 5:17 pm I can see 3 colors besides the white. The blue is obvious. What they call purple I would think is the color that looks more precisely like lavender. And the red looks more like a burgundy color. Am I wrong?
De58te: I see colors like you describe.

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Re: APOD: The Spinning Pulsar of the Crab Nebula (2022 Aug 21)

Post by Chris Peterson » Sun Aug 21, 2022 10:10 pm

Here are all the possible permutations mapping the three input channels to native display primaries. They clearly emphasize different features.
_
crab_mappings.jpg
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