APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

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APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by APOD Robot » Sun Apr 02, 2023 4:08 am

Image M57: The Ring Nebula from Hubble

Explanation: It was noticed hundreds of years ago by stargazers who could not understand its unusual shape. It looked like a ring on the sky. Except for the rings of Saturn, the Ring Nebula (M57) may be the most famous celestial circle. We now know what it is, and that its iconic shape is due to our lucky perspective. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of an (American) football-shaped cloud of glowing gas. Our view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away.

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by AVAO » Sun Apr 02, 2023 6:20 am

APOD Robot wrote: Sun Apr 02, 2023 4:08 am ...The Ring Nebula is about one light-year across and 2,500 light-years away.
Another more distant Ring Nebula at 1 p.m?

Image
APOD 2021 August 18 Composition & Copyright: Robert Gendler
zoom: https://apod.nasa.gov/apod/image/2108/M ... r_3000.jpg

...and I KNOW M57 is a nebula and IC 1296 is a distant galaxy and it is just COINCIDENT that they are so close together,
even if the probability would be practically zero, looking around this almost empty quadrant of space.

Image

Image
jac berne (flickr)
Last edited by AVAO on Sun Apr 02, 2023 6:21 pm, edited 2 times in total.

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by zendae » Sun Apr 02, 2023 6:27 am

I was wondering if the dimmer red gas shrouding the brighter red gas of the ring was the very first stuff that was flung outwards. And if so, would it have different elements in it than the rest of the nebula. Or is the nebula more homogeneous.

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by johnnydeep » Sun Apr 02, 2023 3:17 pm

APOD Robot wrote: Sun Apr 02, 2023 4:08 am Image M57: The Ring Nebula from Hubble

Explanation: It was noticed hundreds of years ago by stargazers who could not understand its unusual shape. It looked like a ring on the sky. Except for the rings of Saturn, the Ring Nebula (M57) may be the most famous celestial circle. We now know what it is, and that its iconic shape is due to our lucky perspective. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of an (American) football-shaped cloud of glowing gas. Our view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away.
We're "looking down the long axis of the football [shaped nebula]"? Really? It seems rather that we are looking down a short axis to me.
Last edited by johnnydeep on Sun Apr 02, 2023 3:52 pm, edited 1 time in total.
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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by orin stepanek » Sun Apr 02, 2023 3:51 pm

M57burgeot.jpg
Very nice pencil work; My opinion! :D
M57Ring_HubbleGendler_960.jpg
Beautiful photo by Hubble! 8-)
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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by Ann » Sun Apr 02, 2023 6:45 pm

zendae wrote: Sun Apr 02, 2023 6:27 am I was wondering if the dimmer red gas shrouding the brighter red gas of the ring was the very first stuff that was flung outwards. And if so, would it have different elements in it than the rest of the nebula. Or is the nebula more homogeneous.
You are absolutely right that the outermost part of the nebula would be the first stuff that was expelled by the dying star.

This gas would be all hydrogen, or more precisely: It would exactly match the composition of the nebula that the star was born from. Also, it would be strongly, strongly dominated by hydrogen. It would also contain a good amount of helium and also very small amounts of heavier elements.

Take a look at the nebula again:


This is a mapped color image. If you go to this page, you can what filters were used for the image and how the filter images were mapped.

A narrowband filter sensitive to light of 658 nm was used. That wavelength is almost the same as ionized hydrogen, but not quite, and to me its sounds more like ionized sulfur or ionized nitrogen. Sulfur and nitrogen only exist as trace elements in the outer atmospheres of stars (and their nebulas), but these elements are nevertheless indeed present, and they will show up if you photograph the nebula through a 658 nm filter. This wavelength is interesting because ionized sulfur and ionized nitrogen represent a lower degree of ionization than ionized hydrogen, even though the photons given off by ionized sulfur and ionized nitrogen are virtually the same as the photons given off by ionized hydrogen.

Another narrowband filter that was sensitive to light of 502 nm was also used. This wavelength corresponds to doubly ionized oxygen, OIII. This light was mapped as green. The parts of the nebula where both red sulfur/nitrogen emission and green OIII emission were detected look yellow in the APOD.

A filter sensitive to light of 469 nm was also used. This wavelength corresponds to ionized helium. Helium is certainly present everywhere in the nebula, but it takes a lot of energy to ionize it, so it is only ionized close to the hot central star of the nebula, the white dwarf. The ionized helium in the Ring Nebula is mapped as blue.

Actually, the filters have been chosen and the filter images have been mapped in such a way that the picture looks quite a lot like a "true color image".

But the outer layers of a planetary nebula are always dominated by hydrogen, unless all of the hydrogen has been cast off and so thoroughly dispersed that it can't be detected at all, which is the case for some planetaries.


You can read about the elements in a planetary nebula here.

Ann

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by BillBixby » Sun Apr 02, 2023 8:26 pm

Thank you to Judy and "the Geek" for this work

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by zendae » Mon Apr 03, 2023 5:14 am

Thank you Ann. It almost sounds like a giant centrifuge of sorts - not working exactly the same way, but having similar results.

Well, we have a limited number of wavelength colors, though many shades. Does each element correspond to a color shade? Can we have 98 shades of color providing the elements are glowing? Do some (or many) never glow? Can we detect non-glowing ones and still ascribe a correct color to them or is that impossible?

For instance, in my a/v field, we cannot have a "brown" light gel expecting to throw "brown" light onto a stage, because isn't "brown" merely very low amplitude yellow? Shine a bright white light thru a brown-colored gel you kinda get yellow. (I am way more audio than visual so I know I'm guessing a bit here). But I am curious if we could possibly see a really colorful nebula if the time were taken to put the thing through lotsa frequencies. I hope I'm making sense here...

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by Ann » Tue Apr 04, 2023 6:58 am

zendae wrote: Mon Apr 03, 2023 5:14 am Thank you Ann. It almost sounds like a giant centrifuge of sorts - not working exactly the same way, but having similar results.

Well, we have a limited number of wavelength colors, though many shades. Does each element correspond to a color shade? Can we have 98 shades of color providing the elements are glowing? Do some (or many) never glow? Can we detect non-glowing ones and still ascribe a correct color to them or is that impossible?

For instance, in my a/v field, we cannot have a "brown" light gel expecting to throw "brown" light onto a stage, because isn't "brown" merely very low amplitude yellow? Shine a bright white light thru a brown-colored gel you kinda get yellow. (I am way more audio than visual so I know I'm guessing a bit here). But I am curious if we could possibly see a really colorful nebula if the time were taken to put the thing through lotsa frequencies. I hope I'm making sense here...
Zendae, you wrote:
Well, we have a limited number of wavelength colors, though many shades.
I'd say we have many many (visible) wavelengths, but our eyes, our cameras, our filters and our processing techniques limit what we can see.


There are huge numbers of wavelengths in the Sun's visible spectrum. It would have been possible, certainly theoretically possible, to create an even more detailed solar spectrum showing even more (visible) wavelengths of the Sun than are seen in the picture above.

In the spectrum, you can see that there are huge numbers of little dark lines showing up everwhere. These are absorption lines, corresponding to wavelengths that have been absorbed (blackened out) by elements in the outer solar atmosphere. However, it is possible (under certain circumstances) to make the elements that "stole" these wavelengths "give them back" again:


So you could, theoretically, have colored light glowing from all the positions of the black lines in the solar spectrum.

Let's talk about photography. When it comes to photography, there are so many factors that limit what can be seen. Since I am a non-photographer, you shouldn't ask me too many questions about it.

Nevertheless, I should be able to say something about the photographic film or filters used to detect color. Take a look at two pictures that I took yesterday with my cheap little mobile phone:

Vitsippan ser blå ut Slottsparken 3 april 2023.jpg
The wood anemone (top) looks blue.
How weird.
Vitsippa Slottsparken 3 april 2023.jpg
True-color white wood anemone.

The picture at left shows two flowers, a wood anemone and a yellow star of Bethlehem. The wood anemone looks blue. The picture at right shows what the wood anemone really looks like: It is white. But the camera in my mobile phone decided to make the wood anemone look blue in the first picture (where the flower is in the shade), and I had no say in the matter.

My mobile phone camera uses no filters, and the picture is taken "all at once". But you can also take filter images. That means that you photograph the same object through different filters that are sensitive to different wavelengths. Take a look at the Hubble Heritage "filter images" of galaxy NGC 4650A:


From these "filter images" you create a composite color picture. Here you can see some suggested images and the one that was actually chosen:


The filters used for the portrait of NGC 4650 were all wideband, i.e, all three filters were sensitive to a wide range of wavelengths centered on 814 nm, 606 nm and 450 nm, respectively. The final image depended on the combination of the sensitivity of the three filters at different wavelengths (and on the people working with the filter images and their abilities and aesthetic choices).


But then there are narrowband images:


The iconic Pillars of Creation image from 1995 is Hubble's first narrowband image. The filters used were 502 nm, ███, for doubly ionized oxygen, 657 nm (Hα + [N II]) ███, for ionized hydrogen and nitrogen, and 673N (S II) ███, for ionized sulfur.

As you can see, ionized hydrogen, ionized nitrogen and ionized sulfur look identical to the human eye, and it is impossible to show the difference between these three ionized elements in either the "all at once" imagery of my mobile phone or in wideband filter images.

NASA solved the problem by assigning different (i would say false) colors to the narrowband filter images. The cyan-green color of 502 nm, ███, was mapped as blue, ███. The red color of 657 nm, ███, was mapped as green, ███. Voila! Problem solved!

But the remaining and (to me) very serious problem is that with narrowband photography, you can choose whatever narrowband wavelength you want to and map it to any color of your choice. There need to be no correspondence between wavelength detected by your camera and filter and the color shown in your final picture.

To see the result of this, consider two versions of Hubble's narrowband portrait of planetary nebula NGC 6826:


So there is one yellow-green version of NGC 6826 and one blue one. But what does NGC 6826 really look like? What color is it really?

Maybe it is this color, ███, 502 nm, for doubly ionized oxygen. Many planetary nebulas are indeed dominated by doubly ionized oxygen, which is cyan-green in color. Not yellow-green. Not blue. Actually, narrowband photography often drives me crazy.

By the way, what colors are the Pillars of Creation really in RGB (red, green, blue) filters? Maybe like this:



Finally, zendae, you asked about dust. Yes, the intrinsic color of cosmic dust is indeed dark reddish or dark brown, which in itself is a version of orange.

Okay, one more. Take a look at one of the absolutely most colorful regions of the sky, the Antares/Rho Ophiuchi region:


The picture shows bright red supergiant Antares, which is really yellow-orange in color. Antares is surrounded by a large yellow reflection nebula. At top is Rho Ophiuchi, a multiple star of spectral class B2, surrounded by a large blue reflection nebula. At right is Sigma Scorpii, a binary star of spectral class B1, surrounded by a reddish-pink hydrogen emission nebula, which is most prominent on the star's right (west) side. In the lower left corner B0V-type star Tau Scorpii is just peeking out, surrounded by a large but dim red emission nebula. Dust lanes and dust bunnies are permeating the images. The thicker the dust is, the darker it is. In places the dust is light brown, almost orange.

Oh, and by the way: Adam Block's picture of the Antares/Rho Ophiuchi region is certainly a "true-color" wideband RGB image! Possibly with the addition of a bit of Hα, to pick up more of the ionized red hydrogen emission.

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Re: APOD: M57: The Ring Nebula from Hubble (2023 Apr 02)

Post by Chris Peterson » Tue Apr 04, 2023 1:16 pm

Ann wrote: Tue Apr 04, 2023 6:58 am My mobile phone camera uses no filters, and the picture is taken "all at once". But you can also take filter images. That means that you photograph the same object through different filters that are sensitive to different wavelengths.
Your mobile phone camera works exactly like astronomical cameras. It takes three separate grayscale images through three broadband red, green, and blue filters and them combines them into a single color image. It uses a technique called "one-shot color" (which many astronomical cameras also use) where the filters are staggered across a single sensor, so the three grayscale frames are coming from a single exposure on a single sensor, but the method and the processing is just like any other multiple filter system.
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