APOD: Messier 20 and 21 (2018 Aug 24)

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APOD: Messier 20 and 21 (2018 Aug 24)

Post by APOD Robot » Fri Aug 24, 2018 4:06 am

Image Messier 20 and 21

Explanation: The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (bottom right). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds. Estimates of the distance to open star cluster M21 are similar to M20's, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21's stars are much older, about 8 million years old.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by FLPhotoCatcher » Fri Aug 24, 2018 4:43 am

Beautiful sight!
I've noted this before, but I will again - there are many star 'chains' visible. More than chance should produce, I think. I even made a simulation of random stars by sprinkling black pepper on a blank paper, and only saw two or three chains of 'stars' out of thousands of ground pepper stars. Has anyone looked to see if there are a significant number of star chains that are actually roughly in a row, and not just appearing to be?
Could we, in the future, 'sail' from one close star to the next, using solar sails to go faster and faster? If the sails were deployed just after closest approach to each star, then retracted after becoming not effective due to distance from the star, the ship could get going very fast using very little fuel. Fuel would be used mostly for correcting course to the next star, and would probably consist of electricity gathered from the stars to power ion drive rockets. Carbon (graphene) seems to be the best material for making solar sails. Cool to think of.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Ann » Fri Aug 24, 2018 4:50 am

APOD Robot wrote:

Estimates of the distance to open star cluster M21 are similar to M20's, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21's stars are much older, about 8 million years old.
I beg to differ, in my amateur way. :wink:

I certainly don't question the age estimates for M20 and M21. I t goes without saying that they formed at different times. But the fact that they are not the same age doesn't have to mean they aren't connected. At least I don't think so.

Take a look at the following wide-angle picture of M8, M20 and M21:

Look at the "skyscape" surrounding M8, M20 and M21. Look at the excess of scattered bright blue stars in the region surrounding M20 and M21. These scattered blue stars seem to form a "bridge" between M20 and M21.

Isn't it possible that the formation of M21 led to repercussions in the surrounding dusty interstellar medium that pervades this entire region, repercussions that compressed the dust cloud that turned into the Trifid Nebula? Alternatively, isn't it possible that both M21 and M20 owe their formation to some other upheaval that has happened in this general region within the last ten million years or so?

M20 and M21 sure look connected. In any case, there is a lot going on in this part of the sky, and this region isn't at all "typical" of the Milky Way when it comes to the number and brightness of its nebulas or the number and brightness and youth of its clusters.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by NCTom » Fri Aug 24, 2018 12:13 pm

I couldn't find the information in the links, but it would seem M21 has a radius of about three to four light years from my limited perspective. How close is this to reality and doesn't this put those 50+ stars in very close proximity, enough to cause gravitational issues?

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by neufer » Fri Aug 24, 2018 1:23 pm

Ann wrote:
Fri Aug 24, 2018 4:50 am

I certainly don't question the age estimates for M20 and M21. I t goes without saying that they formed at different times. But the fact that they are not the same age doesn't have to mean they aren't connected. At least I don't think so.
https://www.universetoday.com/31935/messier-21/ wrote:
Messier 21 (M21) – The NGC 6531 Open Star Cluster
Article written: 1 Aug , 2016 by Tammy Plotner

As Byeong Park of the Korean Astronomy Observatory said in a 2001 study of the object:
In the case of a young open cluster, low-mass stars are still in the contraction phase and their positions in the photometric diagrams are usually crowded with foreground red stars and reddened background stars. The young open cluster NGC 6531 (M21) is located in the Galactic disk near the Sagittarius star forming region. The cluster is near to the nebula NGC 6514 (the Trifid nebula), but it is known that it is not associated with any nebulosity and the interstellar reddening is low and homogeneous.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Sa Ji Tario » Fri Aug 24, 2018 2:03 pm

On average they are three stars per Al cubic for M 21

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Ann » Fri Aug 24, 2018 3:03 pm

neufer wrote:
Fri Aug 24, 2018 1:23 pm

Messier 21 (M21) – The NGC 6531 Open Star Cluster
Article written: 1 Aug , 2016 by Tammy Plotner

As Byeong Park of the Korean Astronomy Observatory said in a 2001 study of the object:
In the case of a young open cluster, low-mass stars are still in the contraction phase and their positions in the photometric diagrams are usually crowded with foreground red stars and reddened background stars. The young open cluster NGC 6531 (M21) is located in the Galactic disk near the Sagittarius star forming region. The cluster is near to the nebula NGC 6514 (the Trifid nebula), but it is known that it is not associated with any nebulosity and the interstellar reddening is low and homogeneous.
Yeah, I could have told you so. Very many young clusters are quite reddened, and the hot stars they contain look yellow or even red when seen from the Earth. Or they could even be so reddened that they are invisible in optical light. Not so M21. The bright stars in there have negative, "blue" B-V indexes.

Then again, the central star of the Trifid Nebula, HD 164492, is also relatively blue in color. And I don't see how it could be unreddened.

Ann
Last edited by Ann on Fri Aug 24, 2018 4:36 pm, edited 1 time in total.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Chris Peterson » Fri Aug 24, 2018 4:36 pm

FLPhotoCatcher wrote:
Fri Aug 24, 2018 4:43 am
Beautiful sight!
I've noted this before, but I will again - there are many star 'chains' visible. More than chance should produce, I think. I even made a simulation of random stars by sprinkling black pepper on a blank paper, and only saw two or three chains of 'stars' out of thousands of ground pepper stars. Has anyone looked to see if there are a significant number of star chains that are actually roughly in a row, and not just appearing to be?
I did a digital simulation of this many years back (a random 3D distribution, viewed from one location) and found many lines, chains, and asterisms. I suspect that your pepper experiment may not have produced a genuinely random distribution, perhaps because of electrostatic forces between the grains.
Chris

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Boomer12k » Fri Aug 24, 2018 9:06 pm

A stunningly beautiful shot... it is just awesome.

My M20 with my 10" Meade and DSI camera...Central Close Up...
From 2013.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by MarkBour » Fri Aug 24, 2018 9:38 pm

Chris Peterson wrote:
Fri Aug 24, 2018 4:36 pm
FLPhotoCatcher wrote:
Fri Aug 24, 2018 4:43 am
Beautiful sight!
I've noted this before, but I will again - there are many star 'chains' visible. More than chance should produce, I think. I even made a simulation of random stars by sprinkling black pepper on a blank paper, and only saw two or three chains of 'stars' out of thousands of ground pepper stars. Has anyone looked to see if there are a significant number of star chains that are actually roughly in a row, and not just appearing to be?
I did a digital simulation of this many years back (a random 3D distribution, viewed from one location) and found many lines, chains, and asterisms. I suspect that your pepper experiment may not have produced a genuinely random distribution, perhaps because of electrostatic forces between the grains.
Also. the pepper experiment described would be a mainly 2-dimensional simulation. Our 2D images of 3D astronomical features must greatly increase the appearance of chains that do not in fact exist.
Capture.JPG



Nevertheless, if you did find a true string of stars somewhere that were quit close together, it seems some great sailing opportunities could be had.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by neufer » Fri Aug 24, 2018 10:40 pm

MarkBour wrote:
Fri Aug 24, 2018 9:38 pm
Chris Peterson wrote:
Fri Aug 24, 2018 4:36 pm
FLPhotoCatcher wrote:
Fri Aug 24, 2018 4:43 am
Beautiful sight!
I've noted this before, but I will again - there are many star 'chains' visible. More than chance should produce, I think. I even made a simulation of random stars by sprinkling black pepper on a blank paper, and only saw two or three chains of 'stars' out of thousands of ground pepper stars. Has anyone looked to see if there are a significant number of star chains that are actually roughly in a row, and not just appearing to be?
I did a digital simulation of this many years back (a random 3D distribution, viewed from one location) and found many lines, chains, and asterisms. I suspect that your pepper experiment may not have produced a genuinely random distribution, perhaps because of electrostatic forces between the grains.
Also. the pepper experiment described would be a mainly 2-dimensional simulation.

Our 2D images of 3D astronomical features must greatly increase the appearance of chains that do not in fact exist.
A random 3D distribution is simply the combination of 3 random 1D distributions.

Every 3 stars will lie on a circular star 'chain.'

There is an excellent chance that at least one of these primary 3 star 'chains'
will pass close to one or more additional stars when viewed 2 dimension-ally.

But one might as well start with a random 2D distribution.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Chris Peterson » Fri Aug 24, 2018 11:13 pm

MarkBour wrote:
Fri Aug 24, 2018 9:38 pm
Chris Peterson wrote:
Fri Aug 24, 2018 4:36 pm
FLPhotoCatcher wrote:
Fri Aug 24, 2018 4:43 am
Beautiful sight!
I've noted this before, but I will again - there are many star 'chains' visible. More than chance should produce, I think. I even made a simulation of random stars by sprinkling black pepper on a blank paper, and only saw two or three chains of 'stars' out of thousands of ground pepper stars. Has anyone looked to see if there are a significant number of star chains that are actually roughly in a row, and not just appearing to be?
I did a digital simulation of this many years back (a random 3D distribution, viewed from one location) and found many lines, chains, and asterisms. I suspect that your pepper experiment may not have produced a genuinely random distribution, perhaps because of electrostatic forces between the grains.
Also. the pepper experiment described would be a mainly 2-dimensional simulation. Our 2D images of 3D astronomical features must greatly increase the appearance of chains that do not in fact exist.
FWIW... 1000 stars randomly distributed in a cube.
_
3d_stars.jpg
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Boomer12k » Sat Aug 25, 2018 3:21 am

As this is kind of fun, I thought I would chime in...

Tangent function on a line

same tangent function randomly spun. 1 and 2. I was trying to create a galaxy. 8-) :lol2:

these are 3D in 2d images... there is a length and depth... some dots would be further away from you...

From any angle and view when spun randomly, you get optically aligned points...2d or 3d, your brain will make a pattern. Whether actually close like an island chain is another matter...I don't think our closest starts are in alignment. In fact, they seem to be all over the place... https://www.space.com/18964-the-nearest ... aphic.html

Long live the Commodore 64!!!
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by FLPhotoCatcher » Sat Aug 25, 2018 9:31 pm

Boomer12k wrote:
Sat Aug 25, 2018 3:21 am
As this is kind of fun, I thought I would chime in...

Tangent function on a line

same tangent function randomly spun. 1 and 2. I was trying to create a galaxy. 8-) :lol2:

these are 3D in 2d images... there is a length and depth... some dots would be further away from you...

From any angle and view when spun randomly, you get optically aligned points...2d or 3d, your brain will make a pattern. Whether actually close like an island chain is another matter...I don't think our closest starts are in alignment. In fact, they seem to be all over the place... https://www.space.com/18964-the-nearest ... aphic.html

Long live the Commodore 64!!!
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I'm guessing the 'chains' of dots in the lower two pics are an artifact of the low resolution or the random function not being truly random. And whether 2D or 3D, random dots should look random in a 2D photo - on average, they would look the same.
As for the pepper sprinkles being statically charged, I don't think so because that would require the air to be dry, but it is fairly humid here, and we only have a window AC. Maybe I didn't look long enough though.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by geckzilla » Sun Aug 26, 2018 6:51 am

Chris Peterson wrote:
Fri Aug 24, 2018 11:13 pm
MarkBour wrote:
Fri Aug 24, 2018 9:38 pm
Chris Peterson wrote:
Fri Aug 24, 2018 4:36 pm


I did a digital simulation of this many years back (a random 3D distribution, viewed from one location) and found many lines, chains, and asterisms. I suspect that your pepper experiment may not have produced a genuinely random distribution, perhaps because of electrostatic forces between the grains.
Also. the pepper experiment described would be a mainly 2-dimensional simulation. Our 2D images of 3D astronomical features must greatly increase the appearance of chains that do not in fact exist.
FWIW... 1000 stars randomly distributed in a cube.
_
3d_stars.jpg
Here's a link to an image that contains the most memorable "chain" of stars I have ever seen after processing however many images.
https://flic.kr/p/tSGXK2
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by neufer » Sun Aug 26, 2018 2:35 pm

Click to play embedded YouTube video.
geckzilla wrote:
Sun Aug 26, 2018 6:51 am

Here's a link to an image that contains the most memorable "chain" of stars I have ever seen after processing however many images.
https://flic.kr/p/tSGXK2
New stars may very well come in chains.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by MarkBour » Tue Aug 28, 2018 12:25 am

Chris Peterson wrote:
Fri Aug 24, 2018 11:13 pm
FWIW... 1000 stars randomly distributed in a cube.
_
3d_stars.jpg
Fascinating example image, Chris. It shows a surprising number of groupings, at least that's what my basic pattern-recognition "feels".
geckzilla wrote:
Sun Aug 26, 2018 6:51 am
Here's a link to an image that contains the most memorable "chain" of stars I have ever seen after processing however many images.
https://flic.kr/p/tSGXK2
And that gorgeous image has an amazing example, as well, Judy. I think I see 12 stars in the apparent "chain" in the lower left of the image, all fairly regularly spaced, though the line is a little "wavy". And a few more stars almost continue the pattern further. And, like Chris' simulation, I see other strings and arcs all over the place in that image.

Even knowing how easily the illusion occurs, those still make one wonder, a little ... maybe that's okay.
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Chris Peterson » Tue Aug 28, 2018 1:27 am

FLPhotoCatcher wrote:
Sat Aug 25, 2018 9:31 pm
And whether 2D or 3D, random dots should look random in a 2D photo - on average, they would look the same.
As for the pepper sprinkles being statically charged, I don't think so because that would require the air to be dry, but it is fairly humid here, and we only have a window AC. Maybe I didn't look long enough though.
Here's a 2D simulation. It looks pretty much like the 3D, with plenty of apparent chains and other patterns. And it is truly random data, not even pseudorandom from an algorithm. The values are generated from random radio noise in the atmosphere.
_
2d_stars.jpg
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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by FLPhotoCatcher » Tue Aug 28, 2018 3:42 am

Chris Peterson wrote:
Tue Aug 28, 2018 1:27 am

Here's a 2D simulation. It looks pretty much like the 3D, with plenty of apparent chains and other patterns. And it is truly random data, not even pseudorandom from an algorithm. The values are generated from random radio noise in the atmosphere.
How do you know the radio noise is truly random? There are some radio signals produced by humans in the mix - the "Wow!" signal comes to mind.

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Re: APOD: Messier 20 and 21 (2018 Aug 24)

Post by Chris Peterson » Tue Aug 28, 2018 4:04 am

FLPhotoCatcher wrote:
Tue Aug 28, 2018 3:42 am
Chris Peterson wrote:
Tue Aug 28, 2018 1:27 am

Here's a 2D simulation. It looks pretty much like the 3D, with plenty of apparent chains and other patterns. And it is truly random data, not even pseudorandom from an algorithm. The values are generated from random radio noise in the atmosphere.
How do you know the radio noise is truly random? There are some radio signals produced by humans in the mix - the "Wow!" signal comes to mind.
You can check out the details and the statistics at random.org. It's pretty much the gold standard for people who need truly random values. Of course, any modern pseudorandom generator would have been more than random enough for this particular application. I was just being extremely rigorous.
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