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Lots of sky glow is actually stars.

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#1 stargazer193857

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Posted 07 September 2019 - 11:58 AM

Look at M31 and complain that it does not stand out well against the washed out background. The dust lanes seem difficult to see even at a dark site.

Then look at an astrophotography. It has tens of thousands of resolved foreground stars and hints of far more fainter ones. We are looking through the Milky Way at the Andromeda Galaxy, even though this area is thinner.

So curse less at the murk. A lot of it is just unresolved stars.

#2 sg6

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Posted 07 September 2019 - 12:28 PM

Haven't you realised that astronomer actively like cursing at the murk?

 

I never did add my opinion to the old question: What do you call a group of astronomers.



#3 Astrojensen

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Posted 07 September 2019 - 12:59 PM

 

The dust lanes seem difficult to see even at a dark site.

No, they're not. Not in my 12", at least. 

 

 

Clear skies!
Thomas, Denmark


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#4 ngc7319_20

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Posted 07 September 2019 - 01:08 PM

There must be fewer foreground stars in Idaho... wink.gif



#5 quazy4quasars

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Posted 08 September 2019 - 01:09 PM

  DSS2 all-sky (Wikisky) imagery, which are "long" exposures (that reveal point sources down to near mag 20)  show the Andromeda Galaxy etc in very good contrast to the surrounding area, and while there are certainly many times more faint stars there than in, for example, the Area around Coma or the very star-poor South Galactic cap (NGC 253 area), I've never felt like it was at a  level of haze or "murk" so as to affect the view of M31 at all.  In a clear, dark sky, the dust lanes are quite obvious.

 

 How would that purported "murk" level of unresolved star contamination compare to that of natural airglow, which affects the whole sky?  Neither are at a level that materially affect contrast in the DSS images, so is it likely that our eyes would notice such a small difference?.  Short of moving M31 to Coma for a comparison view...  anyway, interesting observation!  Perhaps in the case of very low surface brightness objects (Dimmer than the dust lanes in M31), then, perhaps it would be an issue...

 

 I was observing in the Sierra, about 60 miles south of Reno, Nevada, a few weeks ago, and Reno's intense, grey- yellowish light dome appeared as if some gigantic vehicle were shining its high beams at us from just behind the ridgeline. The Milky Way was visible, as was M31, but they would have looked brighter and more impressive -if there were not that hideous bright dome of waste-light, bright enough to affect the entire sky!   My point is that, actually, for most of us, a lot of light pollution is not stars, even when we're out at our (formerly darker) dark sites.  The group I was co-hosting drove for 5 hours to see the heavens in  "pristine" mountain skies...  and 5 more hours to get home. 

 

  So I will continue to (very quietly) curse the Man-Made Murk, sucking the life out of the Heavens as it does; an evil "false dawn" like unto the fires of Mordor- raging in some tantrum of Sauron.

 

sg6, We need closure on that anecdote.


Edited by quazy4quasars, 08 September 2019 - 11:34 PM.


#6 Tony Flanders

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Posted 09 September 2019 - 06:08 AM

Look at M31 and complain that it does not stand out well against the washed out background. The dust lanes seem difficult to see even at a dark site.

Then look at an astrophotography. It has tens of thousands of resolved foreground stars and hints of far more fainter ones. We are looking through the Milky Way at the Andromeda Galaxy, even though this area is thinner.

So curse less at the murk. A lot of it is just unresolved stars.

First of all, as Thomas says, there's nothing subtle about M31's dust lanes when seen through a reasonably big scope (at least 6 or 8 inches) under dark skies.

 

Second, the natural background glow of the sky has been studied in detail, and it turns out that except right in the heart of the Milky Way, the glow of faint stars is a fairly minor contributor. Airglow and the zodiacal light are the main culprits.

 

The only place I've found glow from unresolved stars to be an issue is in the densest part of the Milky Way and the immediate vicinity of a globular cluster.


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#7 Roragi

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Posted 09 September 2019 - 06:16 AM

I can see dust lane with my 4" scope, When someone growls so much it is because they don't like visual astronomy.


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#8 quazy4quasars

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Posted 10 September 2019 - 04:01 PM

  DSS2 all-sky (Wikisky) imagery, which are "long" exposures (that reveal point sources down to near mag 20)  show the Andromeda Galaxy etc in very good contrast to the surrounding area, and while there are certainly many times more faint stars there than in, for example, the Area around Coma or the very star-poor South Galactic cap (NGC 253 area), I've never felt like it was at a  level of haze or "murk" so as to affect the view of M31 at all.  In a clear, dark sky, the dust lanes are quite obvious.

 

 How would that purported "murk" level of unresolved star contamination compare to that of natural airglow, which affects the whole sky?  Neither are at a level that materially affect contrast in the DSS images, so is it likely that our eyes would notice such a small difference?.  Short of moving M31 to Coma for a comparison view...  anyway, interesting observation!  Perhaps in the case of very low surface brightness objects (Dimmer than the dust lanes in M31), then, perhaps it would be an issue...

 

 I was observing in the Sierra, about 60 miles south of Reno, Nevada, a few weeks ago, and Reno's intense, grey- yellowish light dome appeared as if some gigantic vehicle were shining its high beams at us from just behind the ridgeline. The Milky Way was visible, as was M31, but they would have looked brighter and more impressive -if there were not that hideous bright dome of waste-light, bright enough to affect the entire sky!   My point is that, actually, for most of us, a lot of light pollution is not stars, even when we're out at our (formerly darker) dark sites.  The group I was co-hosting drove for 5 hours to see the heavens in  "pristine" mountain skies...  and 5 more hours to get home. 

 

  So I will continue to (very quietly) curse the Man-Made Murk, sucking the life out of the Heavens as it does; an evil "false dawn" like unto the fires of Mordor- raging in some tantrum of Sauron.

 

sg6, We need closure on that anecdote.

 

-One thing I should mention- the most poignant thing of all, really; was that, while I was silently deploring the light pollution form Reno, Sixty miles away; nowhere near far enough; the students in the group (who had all driven up from the Monterey Bay area) were all THRILLED with what we could see, in a much darker sky than they were accustomed to... That was such a saving grace!

 

 We had really good (filtered) views of the Veil, after all, and one or two students were actually pleased to glimpse -a Quasar! (PG 1718+481) among so many tantalizing sights we enjoyed, those nights; M31, dust lanes etc, included.

 

 One young lady (lovely even by the wan light of Reno skyglow) told me that M5, glorious in the 17.5" in the dark southwest-  was the most beautiful thing she had ever seen.  I have no reason to believe she was kidding.cool.gif I'll have that forever. I already knew: M5 is way prettier than me...Thanks, Universe!


Edited by quazy4quasars, 10 September 2019 - 07:51 PM.

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#9 Migwan

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Posted 10 September 2019 - 07:40 PM

One incredible winter night, the dust lanes were so obvious thru my ST80, that I thought something was wrong.  Took awhile for me to accept that it was real.   Haven't had as good a night with my ST120 yet, but have been able to make out the dust lanes often enough with it.    Transparency is key.   It also seems to help to have better than a 3.5° field of view.    jd


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#10 quazy4quasars

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Posted 10 September 2019 - 08:25 PM

Man, that sounds wonderful!  Sometimes those dust lanes... really shine? lol.gif   Especially when near the zenith, too! 

 

Has anyone else noticed how the Northern Coalsack (between Cygnus and Cepheus) often seems like the darkest place in the entire sky?  That cloud must not be too far off -and very little in between, too, I imagine.


Edited by quazy4quasars, 10 September 2019 - 08:38 PM.


#11 Tyson M

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Posted 10 September 2019 - 10:40 PM

I still havent convincingly seen a dust lane in M31.  I have seen it many times at dark sites.  Which area of it seems to be the easiest to discern? The top by M110?  Perhaps I am just seeing it but missing it.



#12 quazy4quasars

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Posted 11 September 2019 - 10:54 AM

I still havent convincingly seen a dust lane in M31.  I have seen it many times at dark sites.  Which area of it seems to be the easiest to discern? The top by M110?  Perhaps I am just seeing it but missing it.

Interesting.  They show all along that side of M31, ,but strongest in the area between NGC 205 and M110,  or, to put it another way, on the M110 side of the disc, and across from NGC 205.  I say "they" because there are more than one, but the innermost should be easiest, and I do mean easy!  The second is harder, but again, not a problem from a "real" dark site.  The third is quite hard to discern even then. I mean really Super Subtle.

 

It's also true that they show better in faster scopes, at lower powers. Maybe steal a view through a fast Dob next time you're out.  You should be dark adapted and using an eyepiece with an exit pupil reasonably close to the size of your own pupil,  for an f/5 scope, that would mean around a 30mm eyepiece  (30mm / f5 = 6mm exit pupil) or even lower. Once you see them, you may wish to increase magnification a bit and look for some subtle edge detail

 

If you can stay out late or wait and brave the Autumn chill when M31 is near zenith, you will see them better.  If that still does not show at least one of them,  you'll need to go somewhere darker...a lot darker.  Best of luck with this pursuit!   


Edited by quazy4quasars, 11 September 2019 - 11:21 AM.

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#13 Migwan

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Posted 11 September 2019 - 03:09 PM

Don't know why, but I tend to see the on the M32 side more often, right where it comes round that end.   Seems a bit more distinct to me, whereas the one on the M110 side looks bigger but more diffuse.   When that one is evident I have also seen another going round the end away from M32.  

 

What seems to be key for me to see any dust lanes, is that I am seeing at least 3° worth of the galaxy.   The ST80 with a 24ES68 is 4° and the ST120 with the 30APM is 3.5°.   Anything less that the latter and I have not been able to make out the dust lanes.     Still waiting for another exceptional night so the ST120 can hopefully match the view I had in the ST80, which is why I bought it.  

 

jd


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