Starship Asterisk*

by **johnnydeep** » Mon Jun 08, 2020 2:54 pm

Chris Peterson wrote: ↑Sun Jun 07, 2020 4:18 pm
johnnydeep wrote: ↑Sun Jun 07, 2020 4:08 pm I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?
Back when men were men and giants walked the Earth, "nightskylive.net" was the host of the APOD discussion forums. So old links may still point the wrong place. I ran into this recently rebuilding my website. I had old links to APOD discussions I needed to fix. Somebody needs to do some kind of global search and replace in order to update the entire APOD site, however.

And who is that "somebody" these days? Is there an official web master?

by **Chris Peterson** » Sun Jun 07, 2020 4:18 pm

johnnydeep wrote: ↑Sun Jun 07, 2020 4:08 pm I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?

Back when men were men and giants walked the Earth, "nightskylive.net" was the host of the APOD discussion forums. So old links may still point the wrong place. I ran into this recently rebuilding my website. I had old links to APOD discussions I needed to fix. Somebody needs to do some kind of global search and replace in order to update the entire APOD site, however.

by **johnnydeep** » Sun Jun 07, 2020 4:08 pm

I just noticed something odd about the APOD page for this (https://apod.nasa.gov/apod/ap130530.html). If you click on the Discuss link there, it takes you to http://bb.nightskylive.net/asterisk/dis ... ate=130530, which ends up being a broken link and falls back to a page that proclaims "The domain nightskylive.net may be for sale. Click here for more details". What the heck? I was able to get to the correct page (http://asterisk.apod.com/viewtopic.php?t=31462) by trying the link http://asterisk.apod.com/discuss_apod.php?date=130530 which redirected to the more familiar format - at least to me - of http://asterisk.apod.com/viewtopic.php?t=31462. So, was this the result of some maintenance script gone wrong?

by **MargaritaMc** » Sat Jun 01, 2013 8:16 pm

Beyond wrote:Amazing!! A Wheely fast whizzing snail from the Wheely Whizzer that has no wheels to whizz with. ((that's almost a tongue twister))

Do NOT try to say that if you've been visiting the Gas Cloud G34.3

http://asterisk.apod.com/viewtopic.php? ... 50#p200324

Margarita

by **Beyond** » Sat Jun 01, 2013 8:07 pm

Amazing!! A Wheely fast whizzing snail from the Wheely Whizzer that has no wheels to whizz with. ((that's almost a tongue twister))
Either the wheels are too small to see, or it puts out slime as fast as a rotating one-armed galaxy.

by **MargaritaMc** » Sat Jun 01, 2013 7:52 pm

Beyond wrote:And here all along i was thinking that you guys were FAST Looks like the gecko will have to make up a new smilie, perhaps a 'whizzing' snail

whizzing_snail.jpeg

by **Beyond** » Sat Jun 01, 2013 7:41 pm

And here all along i was thinking that you guys were FAST

Looks like the

gecko will have to make up a new smilie, perhaps a 'whizzing' snail

by **Ann** » Sat Jun 01, 2013 6:09 pm

Thanks to Case and Margarita for your fascinating snails!

Ann

by **MargaritaMc** » Sat Jun 01, 2013 5:47 pm

geckzilla wrote:Looks like you found a cosmic snail to me, Case.

Any similarity to this?

NGC 772

Nautilus shell

Both from
http://www.stardoctor.org/772.html

Margarita

by **geckzilla** » Sat Jun 01, 2013 5:26 pm

Looks like you found a cosmic snail to me, Case.

by **Case** » Sat Jun 01, 2013 5:10 pm

If I crank up the brightness of this APOD, two features stand out to me. (1) the arm of the spiral galaxy seems to end rather abruptly at the 2 o’clock position, instead of “fading out” like it does towards the outside, and (2) there seems to be a “cavity” of lesser star density towards the 8 o’clock position. [Unless I'm making processing artifacts more visible.]

by **rstevenson** » Sat Jun 01, 2013 12:45 pm

Tara_Li wrote:Why wouldn't a large starbirth nebula, such as the Orion Complex (but perhaps a bit larger) work for that purpose? At what density regime does the Interstellar Medium quit being gravity dominated, and become a fluid? We see turbulance and bowshock in very low density nebulae, after all.

One indication that a star forming nebula has insufficient mass to act as a local center of gravity is that after the star formation period ends, the bright new stars are often seen to have proper motions quite different from each other (within the overall motion of the now-dissipated cloud of gas and dust) and they subsequently wander away. The Sun was born in such a region almost 5 billion years ago, but scientists have so far been unable to identify with certainty any of its birth companions.

Of course, clusters can form and remain gravitationally bound, but judging from the location of the clusters that we can see, this doesn't happen within the more crowded regions of a galaxy and therefore can't produce the eddy that sparked this conversation.

Rob

by **neufer** » Sat Jun 01, 2013 10:30 am

Qexilber wrote:
Hi you guys!

I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?

Hi Qexilber! (Quicksilver?)

It is indeed a second arm: http://asterisk.apod.com/viewtopic.php? ... 62#p200213

Qexilber wrote:
And what are the two light clouds on the left?

Distant galaxies (or possibly companion dwarf galaxies of NGC 4712).

by **Ann** » Sat Jun 01, 2013 6:14 am

Qexilber wrote:Hi you guys!
I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?
And what are the two light clouds on the left?

Yours,
Qexilber

You may well be right that there are hints of a second arm in NGC 4725. For a spiral to have one well-developed arm and no obvious sign of another is so unusual that it is quite probable that NGC 4725 really does have an "embryonic" second arm.

As for the light clouds on the right, I'd say they are probably dwarf spheroidal satellite galaxies. In the image on the left you can see one of the dwarf spheroidal galaxies that are satellites of the Milky Way. These small galaxies lack star formation, so they contain no young blue stars. Therefore their color is grayish or neutral. They contain very few stars compared with a large galaxy, and their "surface brightness" is low. This kind of galaxies look like faint non-blue smudges.

Ann

by **Tara_Li** » Sat Jun 01, 2013 5:09 am

rstevenson wrote:
Tara_Li wrote:
rstevenson wrote:Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. ...
Except that aren't planets supposed to collapse from eddies in the dust clouds around the stars? Sure, there's some magnetic effects in play, but the primary force in the protoplanetary disk is gravity. "Fluid" is kind of a fluid term, really...
Yes, but that's because the gas and dust in a newly forming stellar system can form local aglomerations which gravitationally coalesce into planets. But to get an eddy on a galactic scale you'd need to figure out some way to get entire stellar systems - a great many of them in a group, if they're to appear to us as an eddy - to loop around as they orbit the galactic center of gravity. In other words, they'd need a local center of gravity around which to orbit, just like planets orbit around their star. Conceivably a black hole could collect a few stellar systems around itself, and drag them around the galaxy as it orbits. But I don't think that is gravitationally stable in the long run. It would make for an interesting modelling exercise though.

Why wouldn't a large starbirth nebula, such as the Orion Complex (but perhaps a bit larger) work for that purpose? At what density regime does the Interstellar Medium quit being gravity dominated, and become a fluid? We see turbulance and bowshock in very low density nebulae, after all.

by **Qexilber** » Fri May 31, 2013 10:09 pm

Hi you guys!
I am new here and wanted to ask what these marked features are in yesterdays APOD:

I know, there are hints that there is only one arm but what is this faint thing that looks like a second arm of NGC 4725?
And what are the two light clouds on the left?

Yours,
Qexilber

by **Chris Peterson** » Fri May 31, 2013 2:03 pm

Tara_Li wrote:Except that aren't planets supposed to collapse from eddies in the dust clouds around the stars? Sure, there's some magnetic effects in play, but the primary force in the protoplanetary disk is gravity. "Fluid" is kind of a fluid term, really...

No, the primary force in the protoplanetary disc isn't gravity. The density of the disc is high enough that you have fluid dynamic mechanisms in play. That's what allows the formation of eddies, and it's what allows the system to collapse, heating up and creating the central star in the first place. Once you have accretion and the remaining dust and gas is blown away by the protostar, the system becomes almost completely gravity dominated. Outside of occasional collisions and near misses, there is very little energy or momentum transfer, and the system is essentially stable.

by **rstevenson** » Fri May 31, 2013 1:51 pm

Tara_Li wrote:
rstevenson wrote:Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. ...
Except that aren't planets supposed to collapse from eddies in the dust clouds around the stars? Sure, there's some magnetic effects in play, but the primary force in the protoplanetary disk is gravity. "Fluid" is kind of a fluid term, really...

Yes, but that's because the gas and dust in a newly forming stellar system can form local aglomerations which gravitationally coalesce into planets. But to get an eddy on a galactic scale you'd need to figure out some way to get entire stellar systems - a great many of them in a group, if they're to appear to us as an eddy - to loop around as they orbit the galactic center of gravity. In other words, they'd need a local center of gravity around which to orbit, just like planets orbit around their star. Conceivably a black hole could collect a few stellar systems around itself, and drag them around the galaxy as it orbits. But I don't think that is gravitationally stable in the long run. It would make for an interesting modelling exercise though.

Rob

by **Tara_Li** » Fri May 31, 2013 1:21 pm

rstevenson wrote:Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. Any seeming eddy in an image of a galaxy will either be a background galaxy or a much smaller colliding galaxy, as in the image you linked to Ann. In that case I don't think eddy is quite the right word. An eddy is "a current ... running contrary to the main current; especially : a circular current : whirlpool" according to one on-line dictionary. It's that contrariness that can't spontaneously appear in gravitational systems. And if it does come about because of a galaxy collision, it is really just an independant gravitational system only temporarily operating near the larger system. It will pass through and be disrupted as it does so, so it wouldn't be right to call it an eddy of the larger system.

Except that aren't planets supposed to collapse from eddies in the dust clouds around the stars? Sure, there's some magnetic effects in play, but the primary force in the protoplanetary disk is gravity. "Fluid" is kind of a fluid term, really...

by **rstevenson** » Fri May 31, 2013 12:44 pm

Ann wrote:
Tara_Li wrote:One thing I find interested in a little knot in the arm of the galaxy, at about the 5:30 position. I can't quite tell if it's a small region of sub-rotation, or another galaxy in the background. Be kind of neat, though, to actually find a galaxy with a notable eddy spiral in one of its arms.
I agree with Geckzilla that it is probably a background galaxy, but in my humble amateur opionon, it could actually be an eddy in the arm of NGC 4725.

There exists one definite example of a smallish spiral galaxy that clearly sits in a tidal feature connecting two galaxies. Take a look at this Hubble image of NGC 6050 and IC 1179. This interacting pair is also known as Arp 272. As you can see, there is most definitely a third galaxy involved in this cosmic dance.

Eddies can appear in fluid dynamics but not, I think, when the dynamism of a system is driven by gravity. Any seeming eddy in an image of a galaxy will either be a background galaxy or a much smaller colliding galaxy, as in the image you linked to Ann. In that case I don't think eddy is quite the right word. An eddy is "a current ... running contrary to the main current; especially : a circular current : whirlpool" according to one on-line dictionary. It's that contrariness that can't spontaneously appear in gravitational systems. And if it does come about because of a galaxy collision, it is really just an independant gravitational system only temporarily operating near the larger system. It will pass through and be disrupted as it does so, so it wouldn't be right to call it an eddy of the larger system.

Rob

by **Ann** » Fri May 31, 2013 4:42 am

Tara_Li wrote:One thing I find interested in a little knot in the arm of the galaxy, at about the 5:30 position. I can't quite tell if it's a small region of sub-rotation, or another galaxy in the background. Be kind of neat, though, to actually find a galaxy with a notable eddy spiral in one of its arms.

I agree with Geckzilla that it is probably a background galaxy, but in my humble amateur opionon, it could actually be an eddy in the arm of NGC 4725.

There exists one definite example of a smallish spiral galaxy that clearly sits in a tidal feature connecting two galaxies. Take a look at this Hubble image of NGC 6050 and IC 1179. This interacting pair is also known as Arp 272. As you can see, there is most definitely a third galaxy involved in this cosmic dance.

Ann

by **geckzilla** » Fri May 31, 2013 4:10 am

I'd say that's a background galaxy, Tara. If you search for more images of NGC 4725, you can find some which make it more apparent because the photographers used different processing or imaging techniques.

by **Tara_Li** » Fri May 31, 2013 4:02 am

One thing I find interested in a little knot in the arm of the galaxy, at about the 5:30 position. I can't quite tell if it's a small region of sub-rotation, or another galaxy in the background. Be kind of neat, though, to actually find a galaxy with a notable eddy spiral in one of its arms.

by **Ann** » Fri May 31, 2013 2:27 am

neufer wrote:
[url=http://static.ddmcdn.com/gif/galaxy-8.gif][size=200]Another Sc galaxy[/size][/url][b][color=#0000FF][size=175] bites the dust in the well-groomed constellation Coma Berenices[/size][/color][/b]
Ann wrote:
Well, NGC 4314 isn't one-armed, but instead it is a perfect example of a highly evolved but still recognizable grand design two-armed spiral.
I never said that it was. But it wouldn't take much Wild-Root Cream-Oil to get that cowlick down into a single arm.

Love that cartoon, Art! The disheveled man really does look like an Sc galaxy, or at least his hair does!

Ann

by **Ann** » Fri May 31, 2013 12:30 am

MargaritaMc wrote:
Ann wrote:>>>
What other one-armed spirals do you know of, Art, apart from NGC 4725? You mean NGC 772?

Ann
I'm somewhat confused.
When I looked at images of NGC 772/Arp 78, as in this Apod, I see TWO arms, originating very near each other.

This astrophotographer says
NGC 772 is both huge and distant. Despite its distance of 106 million light years in the constellation Aries, NGC 772 is twice the diameter of our Milky Way Galaxy, allowing us to see detailed structure. The asymmetric spiral arms are distorted by interaction with the dwarf elliptical galaxy NGC 770 at the 1:00 position. Stars stewn outward from NGC 770 appear as a fine haze extending away from the pair.

I find the shape of NGC 772 resembles the nautilus shell, as illustrated to the right, so I have called it the Nautilus Galaxy..

Margarita

I didn't mean to imply that NGC 772 is one-armed, Margarita. It does indeed have two arms. Art's comment about how easy it is to make one-armed spiral galaxies made me leaf through my galaxy atlas, The Colour Atlas of Galaxies by James D Wray, and NGC 772 was the only moderately one-armed looking one that I could find after a very quick search.

The point I was trying to make is that one-armed spirals are very rare and therefore not easy to make at all.

Ann

Starship Asterisk*

APOD: One Armed Spiral Galaxy NGC 4725 (2013 May 30)

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