APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

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APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by APOD Robot » Mon Jan 01, 2024 5:05 am

Image NGC 1232: A Grand Design Spiral Galaxy

Explanation: Galaxies are fascinating not only for what is visible, but for what is invisible. Grand spiral galaxy NGC 1232, captured in detail by one of the Very Large Telescopes, is a good example. The visible is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms revolving about the center. Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them. Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy. Leading theories indicate that even greater amounts of matter are invisible, in a form we don't yet know. This pervasive dark matter is postulated, in part, to explain the motions of the visible matter in the outer regions of galaxies.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by jks » Mon Jan 01, 2024 5:13 am

Wonderful image, and Happy New Year!

Currently, the date above the image reads "2024 January 3".

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by HellCat » Mon Jan 01, 2024 5:40 am

Came to say the same.

Happy New Year all!

3 jan, indeed. The year goes by fast enough as it is.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Ann » Mon Jan 01, 2024 9:43 am

First of all, A Happy New Year everyone! 🌟 💫 ⚡️ And indeed, the date of this image must be changed, from January 3 to January 1.

And... oh well. There is finally a galaxy image as an APOD, and I'm critical of it. :(


First of all, this is a very old image, from 1998. It's not wrong to show old images, but if an image is old you should acknowledge its age and give a reason for why the picture is still relevant.

Second, the colors are weird. They really are. We can see that there are emission nebulas in this galaxy, and we should be able to see red or pink color in at least some of them. Yet we don't. And the arms are very harshly, unnaturally blue.

The reason for the weird colors is the filters chosen for the image. The filters were 360 nm, an ultraviolet filter, 420 nm, a fairly deep dark purple filter, ███, and 600 nm, a yellow-orange filter, ███.

It is clear that you can't construct a picture from ultraviolet, purple and orange filters that matches what our eyes would see, if our organs of vision were enormously sensitive to the faint light emitted by galaxies. You would need RGB filters for that: ███, ███, ███.

By using RGB filters, you could indeed create a picture of NGC 1232 that matches what our eyes would see, if they were thousands of times more sensitive.

Interestingly, there exists another ESO picture (well, an ESO/IDA/Danish 1.5 meter telescope picture) of NGC 1232. That picture is a bit younger too, from 2009. I definitely like that picture better than the APOD:


If you look carefully at the ESO/IDA/Danish telescope image, you can indeed see little pink spots in the arms of NGC 1232, marking the presence of emission nebulas. Also note that the arms are not as harshly unnaturally blue as they are in the APOD. That is because this image has been created from exposures through RVB filters, which closely resemble RGB filters.

My second complaint regarding the APOD is this:

NGC 1232 is not a grand design galaxy!

Yes, I know that the Wikipedia entry on NGC 1232 claims that it is a grand design galaxy. Well, I'd say they are wrong:
Wikipedia wrote:

NGC 1232 is a face-on spiral galaxy. It can be technically considered a Grand-design galaxy and is considered a prototype for multi-arm spiral galaxies.
That is a contradiction in terms!
Wikipedia wrote:

A grand design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms, as opposed to multi-arm and flocculent spirals which have subtler structural features.

I wouldn't go so far as to call NGC 1232 a flocculent galaxy, because it clearly is not. But a multi-armed galaxy shouldn't be described as a grand design galaxy.

If you want to see a beautiful grand design galaxy, then consider NGC 1566, the Spanish Dancer galaxy:


A stunning image, isn't it? Note how well-defined the two main arms of NGC 1566 really are. That's a grand design galaxy if I ever saw one!

Note all the red light from emission nebulas, which have become so visible thanks to the use of an NII filter at 658 nm, very close to hydrogen alpha at 656 nm. The image has also been constructed from exposures through two ultraviolet filter, one image through a 438 nm filter (close to the "ideal " 440 nm blue filter) one image through a 555 nm filter (close to the "ideal" green filter) and one image through a near-infrared 814 nm filter. That's a truly great choice of filters for creating an image that closely matches what our eyes would see if they were thousands of times more sensitive to the faint light of galaxies!

I hope the APOD will feature a beautiful galaxy picture soon that is more recent than from 1998 and which has been constructed from a more RGB-like set of filters than today's APOD!

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Christian G. » Mon Jan 01, 2024 1:47 pm

What better way to start the New Year than with a grand galaxy!

None

Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by None » Mon Jan 01, 2024 2:57 pm

Love the site and the posts, but wish you would not use the word "design" in captions because the of implications of science's adversary called "creationism."

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by RJN » Mon Jan 01, 2024 3:06 pm

jks wrote: Mon Jan 01, 2024 5:13 am Wonderful image, and Happy New Year!

Currently, the date above the image reads "2024 January 3".
Yes, thanks for pointing this out. My bad. Just fixed it.
- RJN

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 3:10 pm

None wrote: Mon Jan 01, 2024 2:57 pm Love the site and the posts, but wish you would not use the word "design" in captions because the of implications of science's adversary called "creationism."
I've certainly never interpreted "grand design" in this context as implying a designer (any more than I've considered "island universe" to imply another universe). This is simply the historical and widely used terminology.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by johnnydeep » Mon Jan 01, 2024 4:05 pm

Somehow, I thought a "grand design" spiral galaxy was one with not only well defined spiral arms (as Ann stated), but specifically, with only TWO arms.

Also:
billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy
Is the mass of the dim normal stars and gas so much greater than the mass of the brighter stars and dust? And it if is, I would think it would dominate the dynamics of the entire galaxy, not just its inner portion. (And yes, there's probably much more dark matter present than the total mass of all the normal matter.)
Last edited by johnnydeep on Mon Jan 01, 2024 4:25 pm, edited 1 time in total.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 4:21 pm

johnnydeep wrote: Mon Jan 01, 2024 4:05 pm Somehow, I though a "grand design" spiral galaxy was one with not only well defined spiral arms (as Ann stated), but specifically, with only TWO arms.
The term has no formal definition. It is a colloquialism commonly applied to any face-on galaxy with any number of reasonably well-defined arms, and it's a matter of subjective opinion in any given case whether the term is reasonable. I'm fine with using the term for NGC 1232, but like I said, it's subjective.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by johnnydeep » Mon Jan 01, 2024 4:28 pm

Chris Peterson wrote: Mon Jan 01, 2024 4:21 pm
johnnydeep wrote: Mon Jan 01, 2024 4:05 pm Somehow, I thought a "grand design" spiral galaxy was one with not only well defined spiral arms (as Ann stated), but specifically, with only TWO arms.
The term has no formal definition. It is a colloquialism commonly applied to any face-on galaxy with any number of reasonably well-defined arms, and it's a matter of subjective opinion in any given case whether the term is reasonable. I'm fine with using the term for NGC 1232, but like I said, it's subjective.
Ok. I think I got the two arm idea from here:
https://en.wikipedia.org/wiki/Messier_74 wrote: Messier 74 (also known as NGC 628 and Phantom Galaxy) is a large spiral galaxy in the equatorial constellation Pisces.[a] It is about 32 million light-years away from Earth.[6] The galaxy contains two clearly defined spiral arms and is therefore used as an archetypal example of a grand design spiral galaxy.[7]
But I guess "archetypal" doesn't mean that its particular form is the full definition, just the "ideal".
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Ann » Mon Jan 01, 2024 5:29 pm

Chris Peterson wrote: Mon Jan 01, 2024 4:21 pm
johnnydeep wrote: Mon Jan 01, 2024 4:05 pm Somehow, I though a "grand design" spiral galaxy was one with not only well defined spiral arms (as Ann stated), but specifically, with only TWO arms.
The term has no formal definition. It is a colloquialism commonly applied to any face-on galaxy with any number of reasonably well-defined arms, and it's a matter of subjective opinion in any given case whether the term is reasonable. I'm fine with using the term for NGC 1232, but like I said, it's subjective.
I'm not.

Take a look at NGC 521. Would you call it a grand design galaxy? Note that the arms are quite well defined.


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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Roy » Mon Jan 01, 2024 5:55 pm

None wrote: Mon Jan 01, 2024 2:57 pm Love the site and the posts, but wish you would not use the word "design" in captions because the of implications of science's adversary called "creationism."
Not to quibble, but the whole idea of cosmology today is creation out of nothing. Isn’t this New Year’s Day of the year 700,002,024 of the 15th Aeon?

That galaxy is estimated to be 60 million light years away. Any estimate of how many civilizations we are looking at, or how many have arisen and fallen in the time the light took to arrive? Our species arose maybe 4 million years ago, so it will be another 54 million years for the light from us to get there. Will we stil be around then? Odds seem to be against it.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 5:59 pm

Ann wrote: Mon Jan 01, 2024 5:29 pm
Chris Peterson wrote: Mon Jan 01, 2024 4:21 pm
johnnydeep wrote: Mon Jan 01, 2024 4:05 pm Somehow, I though a "grand design" spiral galaxy was one with not only well defined spiral arms (as Ann stated), but specifically, with only TWO arms.
The term has no formal definition. It is a colloquialism commonly applied to any face-on galaxy with any number of reasonably well-defined arms, and it's a matter of subjective opinion in any given case whether the term is reasonable. I'm fine with using the term for NGC 1232, but like I said, it's subjective.
I'm not.

Take a look at NGC 521. Would you call it a grand design galaxy? Note that the arms are quite well defined.


Ann
I don't see that as having well defined arms. There are weird bridges between them. So I probably wouldn't call it "grand design". I find the arms of NGC 1231 striking and extremely well defined, which for me, is why the term works.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by johnnydeep » Mon Jan 01, 2024 6:29 pm

Chris Peterson wrote: Mon Jan 01, 2024 5:59 pm
Ann wrote: Mon Jan 01, 2024 5:29 pm
Chris Peterson wrote: Mon Jan 01, 2024 4:21 pm
The term has no formal definition. It is a colloquialism commonly applied to any face-on galaxy with any number of reasonably well-defined arms, and it's a matter of subjective opinion in any given case whether the term is reasonable. I'm fine with using the term for NGC 1232, but like I said, it's subjective.
I'm not.

Take a look at NGC 521. Would you call it a grand design galaxy? Note that the arms are quite well defined.


Ann
I don't see that as having well defined arms. There are weird bridges between them. So I probably wouldn't call it "grand design". I find the arms of NGC 1232 striking and extremely well defined, which for me, is why the term works.
I don't see "well defined" arms at all in this image of NGC 1232. If there are, then how many are there and what are their outlines?
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 6:33 pm

johnnydeep wrote: Mon Jan 01, 2024 6:29 pm
Chris Peterson wrote: Mon Jan 01, 2024 5:59 pm
Ann wrote: Mon Jan 01, 2024 5:29 pm

I'm not.

Take a look at NGC 521. Would you call it a grand design galaxy? Note that the arms are quite well defined.


Ann
I don't see that as having well defined arms. There are weird bridges between them. So I probably wouldn't call it "grand design". I find the arms of NGC 1232 striking and extremely well defined, which for me, is why the term works.
I don't see "well defined" arms at all in this image of NGC 1232. If there are, then how many are there and what are their outlines?
I see two well defined arms that appear to spread out and separate only in the outer parts of the galaxy.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by johnnydeep » Mon Jan 01, 2024 6:35 pm

Roy wrote: Mon Jan 01, 2024 5:55 pm
None wrote: Mon Jan 01, 2024 2:57 pm Love the site and the posts, but wish you would not use the word "design" in captions because the of implications of science's adversary called "creationism."
Not to quibble, but the whole idea of cosmology today is creation out of nothing. Isn’t this New Year’s Day of the year 700,002,024 of the 15th Aeon?
...
There are really only two possibilities: either the (multi)universe arose out of nothing (and might be continuing to do so), or there was never anything that arose out of nothing (i.e. everything always was). 😉
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by johnnydeep » Mon Jan 01, 2024 6:48 pm

Chris Peterson wrote: Mon Jan 01, 2024 6:33 pm
johnnydeep wrote: Mon Jan 01, 2024 6:29 pm
Chris Peterson wrote: Mon Jan 01, 2024 5:59 pm

I don't see that as having well defined arms. There are weird bridges between them. So I probably wouldn't call it "grand design". I find the arms of NGC 1232 striking and extremely well defined, which for me, is why the term works.
I don't see "well defined" arms at all in this image of NGC 1232. If there are, then how many are there and what are their outlines?
I see two well defined arms that appear to spread out and separate only in the outer parts of the galaxy.
I don't know. Maybe I'd start the two main arms like so, but I'm not too sure which other branches should be classified as offshoots of which of the primary two.

ngc 1232 arms tentative.jpg
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Ann » Mon Jan 01, 2024 6:55 pm

johnnydeep wrote: Mon Jan 01, 2024 6:48 pm
Chris Peterson wrote: Mon Jan 01, 2024 6:33 pm
johnnydeep wrote: Mon Jan 01, 2024 6:29 pm

I don't see "well defined" arms at all in this image of NGC 1232. If there are, then how many are there and what are their outlines?
I see two well defined arms that appear to spread out and separate only in the outer parts of the galaxy.
I don't know. Maybe I'd start the two main arms like so, but I'm not too sure which other branches should be classified as offshoots of which of the primary two.

I'm with yoiu, Johhny.

But NGC 1232 clearly doesn't have just two well-defined arms. NGC 1232 is the prototypical multi-armed spiral galaxy. I'll grant you that the arms are reasonably well-defined, but there surely aren't just two of them. I also wouldn't be able to say which arms are the main ones and which are just, well, secondary ones.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 6:59 pm

Ann wrote: Mon Jan 01, 2024 6:55 pm
johnnydeep wrote: Mon Jan 01, 2024 6:48 pm
Chris Peterson wrote: Mon Jan 01, 2024 6:33 pm

I see two well defined arms that appear to spread out and separate only in the outer parts of the galaxy.
I don't know. Maybe I'd start the two main arms like so, but I'm not too sure which other branches should be classified as offshoots of which of the primary two.

I'm with yoiu, Johhny.

But NGC 1232 clearly doesn't have just two well-defined arms. NGC 1232 is the prototypical multi-armed spiral galaxy. I'll grant you that the arms are reasonably well-defined, but there surely aren't just two of them. I also wouldn't be able to say which arms are the main ones and which are just, well, secondary ones.

Ann
But a grand design spiral doesn't have to have two arms. Like I said, the term is 100% subjective.
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Ann » Mon Jan 01, 2024 7:05 pm

I think a grand design galaxy should have two main arms. Consider NGC 309:

NGC 309 annotated.png
The main arms of NGC 309 as I see them.

And in my opinion, one of my favorite galaxies, M100 in the Virgo Cluster, is a great example of a grand design galaxy.


I don't have to draw the main arms of M100 for you to see them. Admittedly though, M100 has two broad, faint, old population outer arms that appear to be separate from the high surface brightness and starforming main arms. You can easily see one of the outer arms at right, where it is stretching towards one of M100's satellite galaxies.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Mon Jan 01, 2024 7:30 pm

Ann wrote: Mon Jan 01, 2024 7:05 pm I think a grand design galaxy should have two main arms. Consider NGC 309:

NGC 309 annotated.png
The main arms of NGC 309 as I see them.

And in my opinion, one of my favorite galaxies, M100 in the Virgo Cluster, is a great example of a grand design galaxy.


I don't have to draw the main arms of M100 for you to see them. Admittedly though, M100 has two broad, faint, old population outer arms that appear to be separate from the high surface brightness and starforming main arms. You can easily see one of the outer arms at right, where it is stretching towards one of M100's satellite galaxies.

Ann
Then I suggest you only use the term for such galaxies. I see no reason to myself. No such definition exists. For me, all that is required is that it be close to face-on and have well defined arms (which is itself subjective!)
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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Avalon » Tue Jan 02, 2024 3:46 am

Examples of Fibonacci patterns are found in great numbers in nature. They are designs. To me they indicate a designer, but that is my opinion. The fact that they are designs cannot be denied.

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Ann » Tue Jan 02, 2024 5:05 am

Chris Peterson wrote: Mon Jan 01, 2024 7:30 pm
Ann wrote: Mon Jan 01, 2024 7:05 pm I think a grand design galaxy should have two main arms. Consider NGC 309:

NGC 309 annotated.png
The main arms of NGC 309 as I see them.

And in my opinion, one of my favorite galaxies, M100 in the Virgo Cluster, is a great example of a grand design galaxy.


I don't have to draw the main arms of M100 for you to see them. Admittedly though, M100 has two broad, faint, old population outer arms that appear to be separate from the high surface brightness and starforming main arms. You can easily see one of the outer arms at right, where it is stretching towards one of M100's satellite galaxies.

Ann
Then I suggest you only use the term for such galaxies. I see no reason to myself. No such definition exists. For me, all that is required is that it be close to face-on and have well defined arms (which is itself subjective!)
Okay, Chris. I see your point, I really do. :ssmile: So let's agree to disagree on what a grand design galaxy is.

However, bear in mind that Wikipedia said that a grand design spiral galaxy is a galaxy with clearly defined arms as opposed to multi-armed or flocculent galaxies. NGC 1232 has clearly defined arms, but it is also multi-armed (which, according to Wikipedia, therefore speaks against it being a grand design spiral galaxy). To me that means that you could either argue that NGC 1232 is a grand design galaxy or you could argue that it isn't. Therefore, if you should use just 3-4 words to describe NGC 1232, as in an APOD heading, "a grand design spiral" is not the best choice.

I'll offer a few "perfect" grand design galaxies for your consideration, apart from M100 and NGC 1566 which I have already shown you:

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Re: APOD: NGC 1232: A Grand Design Spiral Galaxy (2024 Jan 01)

Post by Chris Peterson » Tue Jan 02, 2024 5:26 am

Ann wrote: Tue Jan 02, 2024 5:05 am
Chris Peterson wrote: Mon Jan 01, 2024 7:30 pm
Ann wrote: Mon Jan 01, 2024 7:05 pm I think a grand design galaxy should have two main arms. Consider NGC 309:

NGC 309 annotated.png
The main arms of NGC 309 as I see them.

And in my opinion, one of my favorite galaxies, M100 in the Virgo Cluster, is a great example of a grand design galaxy.


I don't have to draw the main arms of M100 for you to see them. Admittedly though, M100 has two broad, faint, old population outer arms that appear to be separate from the high surface brightness and starforming main arms. You can easily see one of the outer arms at right, where it is stretching towards one of M100's satellite galaxies.

Ann
Then I suggest you only use the term for such galaxies. I see no reason to myself. No such definition exists. For me, all that is required is that it be close to face-on and have well defined arms (which is itself subjective!)
Okay, Chris. I see your point, I really do. :ssmile: So let's agree to disagree on what a grand design galaxy is.

However, bear in mind that Wikipedia said that a grand design spiral galaxy is a galaxy with clearly defined arms as opposed to multi-armed or flocculent galaxies. NGC 1232 has clearly defined arms, but it is also multi-armed (which, according to Wikipedia, therefore speaks against it being a grand design spiral galaxy). To me that means that you could either argue that NGC 1232 is a grand design galaxy or you could argue that it isn't. Therefore, if you should use just 3-4 words to describe NGC 1232, as in an APOD heading, "a grand design spiral" is not the best choice.

I'll offer a few "perfect" grand design galaxies for your consideration, apart from M100 and NGC 1566 which I have already shown you:

Ann
To make more clear just how arbitrary the term is, just follow the Wikipedia link to the paper where the term was coined, and we see that it has nothing to do with anything we're talking about here! What the authors say is "...the primary problem we wish to resolve is the persistence of the spiral pattern or the grand design over the whole disk, on the scale of 10 kpc." That's it! Others took it from there and made it mean whatever they wanted... all with no formal or official definition at all.

And the reference Wikipedia provides to its definition is nothing more than some guy's website with an asserted definition! Not much of a reference!

So yeah, it means whatever we want it to mean.
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