APOD: The Cat's Eye Nebula from Hubble (2017 Jan 30)

[APOD Robot]

The Cat's Eye Nebula from Hubble

Explanation: To some, it may look like a cat's eye. The alluring Cat's Eye nebula, however, lies three thousand light-years from Earth across interstellar space. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this digitally reprocessed Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into this Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

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[RocketRon]

And the red color is ??

Beautiful subject, no matter how you view it - art, astronomy, drawing, intricate shapes....

[Ann]

Click to view full size image

NGC 6543, the Cat's Eye Nebula.
Image credit: NASA, J. P. Harrington (U. Maryland) and K. J. Borkowski (NCSU)

Click to view full size image

The Cat's Eye Nebula.
NASA, ESA, Hubble, HLA, Credit and copyright: Raul Villaverde

I think that today's APOD, at right, is a re-processed version of the Hubble image of the Cat's Eye Nebula seen at left.

As a Color Commentator, I was highly critical of the picture of Cat's Eye Nebula seen at left, for two reasons: I found it esthetically unpleasant (a completely subjective opinion), and I found it downright weird to produce a mapped color, almost all red version of an object that will look green or even bluish to the visual observer. Though it is possible that someone like Chris will tell me that the dominant red color of the Cat's Eye Nebula in the Hubble picture was a way of saying that this is not a simple visual-light portrait of the Cat's Eye Nebula, but rather the picture was produced to obtain another set of data than those that are available to the visual astronomer.

I still don't like the picture that I have posted at left, but I must say that Raul Villaverde's version, at right, is a very great improvement on it. Not only are the details so much sharper and the resolution so much better, but the color looks so much better, too!

Ann

[Boomer12k]

Wow, that is spectacularly awesome... it looks like some of it on left and right, ran into something...

:---[===] *

[NCTom]

Can we get an estimate on the expansion rate to know when these series of shells were ejected, how long this process has been going on?

[neufer]

Can we get an estimate on the expansion rate to know when these series of shells were ejected, how long this process has been going on?

<<NGC 6543 has the combined magnitude of 8.1, with high surface brightness. Its small bright inner nebula subtends an average of 16.1 arcsec, with the outer prominent condensations about 25 arcsec.

Some recent Hubble Space Telescope observations of NGC 6543 taken several years apart determine its distance from the [current] angular expansion rate of 3.457 milliarcseconds per year. Assuming a line of sight expansion velocity of 16.4 km/s, this implies that NGC 6543's distance is 1001±269 parsecs (or 3300 light-years) away from Earth.

The angular expansion of the nebula can also be used to estimate its age. If it has been expanding at [an average] rate of 10 milliarcseconds a year, then it would take 1000±260 years to reach a diameter of 20 arcseconds. This may be an upper limit to the age, because ejected material will be slowed when it encounters material ejected from the star at earlier stages of its evolution, and the interstellar medium.>>

[Chris Peterson]

I think that today's APOD, at right, is a re-processed version of the Hubble image of the Cat's Eye Nebula seen at left.

They look like completely different images to me, with the first not obviously a Hubble image at all. Do you have a link to the details?

[Ann]

I think that today's APOD, at right, is a re-processed version of the Hubble image of the Cat's Eye Nebula seen at left.

They look like completely different images to me, with the first not obviously a Hubble image at all. Do you have a link to the details?

The link is here.

I think this picture was a repeat APOD on a Sunday (or a Saturday) some months ago.

Ann

P.S. Here is a better link.

[neufer]

I think that today's APOD, at right, is a re-processed version of the Hubble image of the Cat's Eye Nebula seen at left.

They look like completely different images to me, with the first not obviously a Hubble image at all. Do you have a link to the details?

The link is ... here.

• Today's APOD is no doubt a Hubble TRUE color image:

<<The Hubble Space Telescope image produced here is in false colour, designed to highlight regions of high and low ionisation. Three images were taken, in filters isolating the light emitted by singly ionised hydrogen at 656.3 nm, singly ionised nitrogen at 658.4 nm and doubly ionised oxygen at 500.7 nm. The images were combined as red, green and blue channels respectively, although their true colours are red, red and green. The image reveals two "caps" of less ionised material at the edge of the nebula.>>

[Chris Peterson]

I think that today's APOD, at right, is a re-processed version of the Hubble image of the Cat's Eye Nebula seen at left.

They look like completely different images to me, with the first not obviously a Hubble image at all. Do you have a link to the details?

P.S. Here is a better link.

Thanks. This reinforces my opinion that the two images are made from completely different data sets. The less clear one appears to be framed on one of the 800x800 CCD sensors that made up the WFPC2 instrument. Today's APOD is oriented differently and has a somewhat different image scale. And it appears to have much higher native resolution. I'm inclined to think it was collected from a newer camera.

That said, without more information it's difficult to know what's going on. I still wish that the editors wouldn't choose images where the imager hasn't provided processing details. I think such images are contrary to the entire purpose of APOD.

[Ann]

Today's APOD is no doubt a Hubble TRUE color image

Click to view full size image

NGC 6543. Adam Block/NOAO/AURA/NSF.

I doubt it.

The (quite old) picture by Adam Block at left is in all probability a good true color portrait of the Cat's Eye Nebula. The inner parts of the Cat's Eye are dominated by blue-green OIII emission, while the outer parts are red from Hα. This color gradient is very typical of many planetary nebulas. The Hubble picture, by contrast, makes the inner parts of the Cat's Eye look red and the outer parts green. I strongly doubt that this is even approximately "true color".

Besides, aren't the eyes of cats often green? When did you last see a red-eyed cat?

Ann

[Chris Peterson]

Besides, aren't the eyes of cats often green? When did you last see a red-eyed cat?

[Fred the Cat]

I don't suppose Hubble's camera has a red-eye mode.

[craigpom]

How big is the sun in the cat's eye nebula?
The diameter from the picture is 1/64 the size of the nebula
The nebula is 1/2 light year across
That would make the star about 30 trillion miles in diameter?
Pretty big star!

[Chris Peterson]

How big is the sun in the cat's eye nebula?
The diameter from the picture is 1/64 the size of the nebula
The nebula is 1/2 light year across
That would make the star about 30 trillion miles in diameter?
Pretty big star!

The central star is somewhat smaller than the Sun, probably around a million kilometers in diameter.

Stars are unresolved in astronomical images, given an apparent diameter only because of diffraction effects in the optics. At the scale of this image, the central star is much smaller than a single pixel.

[cosefernando]

Are same data but reprocessed much better, horizontal mirror Is the only geometric difference.

[neufer]

Today's APOD is no doubt a Hubble TRUE color image

I doubt it. The inner parts of the Cat's Eye are dominated by blue-green OIII emission, while the outer parts are red from Hα. This color gradient is very typical of many planetary nebulas. The Hubble picture, by contrast, makes the inner parts of the Cat's Eye look red and the outer parts green. I strongly doubt that this is even approximately "true color".

OK... perhaps blue-green OIII emission dominates visually.

[Thestopper]

Does the star in the center have a name and what would this star look like

[neufer]

Does the star in the center have a name and what would this star look like

• The Planetary nebula nucleus (PNN) of NGC 6543 or HD 164963. (It is very hot & very blue)

<<Surface temperature for the central PNN is about 80,000 K, being 10,000 times as luminous as the sun. Stellar classification is O7 + [WR]–type star. Calculations suggest the PNN is over one solar mass, from a theoretical initial 5 solar masses. The central Wolf-Rayet star has a radius of 0.65 R_☉.>>

[Ann]

I don't suppose Hubble's camera has a red-eye mode.

Click to view full size image

The Rosette Nebula in Hubble palette.
Photo: Filipe Alvez.

Apparently it does!

The picture on the left is admittedly not a Hubble image, but it is a Hubble palette image of a nebula that is completely dominated by red Hα emission. It must be said that not a single red Hα nebula actually looks red to the human eye through the telescope. Nevertheless, I find it noteworthy that many red Hα nebulas are made to look predominantly bluish in Hubble palette images (and in some bona fide Hubble images, too), because there is some OIII emission in the inner parts of them.

Planetary nebulas are different from "ordinary" emission nebulas in that there is extremely little hydrogen in the inner parts of very many of them (depending on their evolutionary state, admittedly, but still), but there is often quite bright OIII emission there. That is why some planetary nebulas really look colored (green) to the visual observer, although basically all other deep-sky objects look colorless to the human eye.

As for the Cat's Eye nebula, it is dominated by OIII emission:

Wikipedia wrote:
However, when Huggins looked at the Cat's Eye Nebula, he found a very different spectrum. Rather than a strong continuum with absorption lines superimposed, the Cat's Eye Nebula and other similar objects showed a number of emission lines.[7] The brightest of these was at a wavelength of 500.7 nanometres, which did not correspond with a line of any known element.

500.7 nanometres is of course the green color of OIII.

Besides, planetary nebulas are called planetaries because the term was coined by William Herschel, shortly after he had discovered Uranus!

Space.com wrote:
The term "planetary nebula" is a misnomer. It was coined by William Herschel, who also compiled an astronomical catalog. Herschel had recently discovered the planet Uranus, which has a blue-green tint, and he thought that the new objects resembled the gas giant.

Planet Uranus. NSA/JPL-Caltech.

Does Uranus often look red through the telescope? I don't think so!

My software, Guide, sometimes quotes an observer, Steve Coe, when describing deep-sky objects. This is what Steve Coe said about the Cat'e Eye Nebula, when he observed it one night back in 1995:

(...) great night near the Grand Canyon, light green, elongated 2X1 in PA 45, central star obvious, small dark donut around the central star. This donut of material is neon green, it really does seem to glow.

So any predominantly red portrait of the Cat's Eye Nebula by Hubble (or by anyone else) is not true color!!!

And as for Hubble, it will sometimes show red objects as bluish and green objects as red!

Ann

[Fred the Cat]

I don't suppose Hubble's camera has a red-eye mode.

Click to view full size image

The Rosette Nebula in Hubble palette.
Photo: Filipe Alvez.

Apparently it does!
Ann

I think we'd agree the Hubble "palate" is à la mode.

[Ann]

I don't suppose Hubble's camera has a red-eye mode.

Apparently it does!
Ann

I think we'd agree the Hubble "palate" is à la mode.

According to Merriam Webster, à la mode means either "fashionable, stylish" or "topped with ice cream" (I didn't know that! Can I have my pancake à la mode?)

I agree that the Hubble palette is fashionable, but I don't think it is stylish. But it might be 'palatable', if it comes with ice cream on top! :yummy:

(Your link, btw, took me to Merriam Webster, and Merriam Webster always makes my computer "freeze". Apparently the ice cream topping is too cold for my PC!)

Ann

[Fred the Cat]

Apparently it does!
Ann

I think we'd agree the Hubble "palate" is à la mode.

According to Merriam Webster, à la mode means either "fashionable, stylish" or "topped with ice cream" (I didn't know that! Can I have my pancake à la mode?)

I agree that the Hubble palette is fashionable, but I don't think it is stylish. But it might be 'palatable', if it comes with ice cream on top! :yummy:

(Your link, btw, took me to Merriam Webster, and Merriam Webster always makes my computer "freeze". Apparently the ice cream topping is too cold for my PC!)

Ann

This might freeze you too but I’ll put it out there. As far as color assignments it isn’t very palatable but I thought the media sounded enticing. A few years ago, I was looking for objects that might be amenable to stained glass. The idea may not be possible, especially when you don’t have the required colors, but I thought I would test the water.

Now I have more time to attempt it again I wonder what celestial subject matter would fit. Any ideas?

[Ann]

Click to view full size image

Cat's Eye Nebula.
NASA, J. P. Harrington (U. Maryland) and K. J. Borkowski (NCSU)

A false-color Cat's Eye Nebula?

Ann