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The affect of moonlight on DSO/ galaxies.

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#1 Ballyhoo

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Posted 26 June 2019 - 05:06 PM

Kind of curious as to what point moonlight becomes a problem. Most visual observes I know will packup once the moon breaches Sunflower, which was prob 80 degrees away.

 

Sub sample 1, near moment of moon-rise (12:03 AM, evening of Jun 23-24.) Waning gibbous .

sample 2, 15 minutes after moon-rise.

Sample 3, 20  min after moon rise

sample 4, 35 min after.

 

Theoretically I could have continued integration and just used dark files. 

 

edit, someone has got to invent a moon filter. they will be a gazillionair.

Attached Thumbnails

  • sunflower  pre moonlight.gif
  • sunflower moonlight 15.gif
  • sunflower  20 moonlight.gif
  • sunflower moonlight.gif

Edited by Ballyhoo, 26 June 2019 - 05:10 PM.

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#2 2ghouls

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Posted 26 June 2019 - 05:16 PM

I typically don't do LRGB or OIII imaging when the moon is up, because as you can see with your samples it is like light pollution in that it severely lowers contrast/ washes out detail.

 

I do almost all my Ha, SII, and NIR (these deep reds seem less affected) imaging with the moon up, but try not to image objects within about 30 degrees of it.

 

 

 



#3 Jerome Ni

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Posted 26 June 2019 - 05:22 PM

Our moon reflects the whole visible spectrum, and being so bright it literally lights up the night sky, so when it's near full and up, it will affect your image quality significantly.

 

I guess when you see your subs being lit by the moon, you probably should stop imaging.

 

The only way to get usable subs under near full moon is to use narrowband filters(mostly Ha) and a mono camera, and even that cannot block the moonlight entirely. I've heard that O3 channel, if not narrow enough, is also going to be significantly affected by the moon.


Edited by Jerome Ni, 26 June 2019 - 05:24 PM.

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#4 AhBok

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Posted 26 June 2019 - 05:38 PM

I avoid imaging (OSC) within 30 degrees of Luna for most phases. I also avoid DSO imaging +\- 4 days of full moon. I’m retired and a night owl, so I plan my imaging to non-moonlight hours when possible. Lately, I’ve been doing planetary imaging when the moon is too bright for DSOs.
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#5 Ballyhoo

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Posted 26 June 2019 - 05:50 PM

But I still am getting a lot of galaxy there even with the moon in force.  I wonder if I tried to integrate w dark frames If I would get any good results.  I mean, the galaxy is still there, right?   I imagine the project would not go well or everyone would be doing it. 



#6 TrustyChords

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Posted 26 June 2019 - 06:00 PM

But I still am getting a lot of galaxy there even with the moon in force.  I wonder if I tried to integrate w dark frames If I would get any good results.  I mean, the galaxy is still there, right?   I imagine the project would not go well or everyone would be doing it. 

I suspect you'll have to deal with more light gradient as you try and bring out more detail, and then as you try and fight the gradient, you'll clip more of the detail.


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#7 TelescopeGreg

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Posted 26 June 2019 - 06:37 PM

Perhaps a related question is that if you are doing LRGB or NB imaging with the Moon rising, isn't that going to mean that the stacks of each type of image are going to be hard to calibrate and mesh together, since each will have a different level of background LP?  Or you could end up flipping between filters for each sub to average it out, but then you'll be spending your night spinning the filter wheel and running the focuser instead of the camera.



#8 2ghouls

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Posted 26 June 2019 - 06:47 PM

But I still am getting a lot of galaxy there even with the moon in force. I wonder if I tried to integrate w dark frames If I would get any good results. I mean, the galaxy is still there, right? I imagine the project would not go well or everyone would be doing it.


Your results will be ok, just not as good if you gathered all your data without moonlight. It’s the exact same as imaging with lots of light pollution vs. going to a dark site. Both will get you results, the latter will just be better.

#9 Ballyhoo

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Posted 26 June 2019 - 07:20 PM

Your results will be ok, just not as good if you gathered all your data without moonlight. It’s the exact same as imaging with lots of light pollution vs. going to a dark site. Both will get you results, the latter will just be better.

So that is why people just dont go out with the moon, because plainly, it will be better without the moon.

 

edit,

I wonder what the equivalent in LP that last pic with moon in full force? Maybe that would be like imaging same object from Freedom Tower in NYC.


Edited by Ballyhoo, 26 June 2019 - 07:22 PM.

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#10 DaveB

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Posted 26 June 2019 - 08:20 PM

Here is a 30 second time-lapse video that I took a couple of years ago. The moon sets behind the camera about halfway through the video. You can see how drastic the difference is with/without the moon. Note that it set around 2:00 am, so it wasn't twilight brightening the video except at the very beginning - it was all moonlight.

 

https://www.youtube....h?v=Fe-yRXkaHg0

 

 


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#11 FiremanDan

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Posted 26 June 2019 - 09:17 PM

But I still am getting a lot of galaxy there even with the moon in force.  I wonder if I tried to integrate w dark frames If I would get any good results.  I mean, the galaxy is still there, right?   I imagine the project would not go well or everyone would be doing it. 

Darks won't change that. Gradient/Background naturalizing tools/programs are how you deal with unwanted light. Same as light pollution. 

5nm Ha and 3nm O3 and S2 work ok with Moon light. I shoot Ha with the moon all the time, 3nm O3 I usually try to be as far away from the Moon as I can even with narrowband. But OSC and LRGB is difficult with Moon light. 

 


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#12 RogeZ

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Posted 26 June 2019 - 10:01 PM

The moon reflects broadband light, so its light cant be filtered out completely but target SNR can be increased with NB filters.

#13 kyle528

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Posted 27 June 2019 - 06:04 AM

But I still am getting a lot of galaxy there even with the moon in force. I wonder if I tried to integrate w dark frames If I would get any good results. I mean, the galaxy is still there, right? I imagine the project would not go well or everyone would be doing it.


Dark frames are taken to calibrate things like thermal noise and amp glow, not light pollution. Imaging with the moon up, yes you might be able to still see the target in the frame, but think about what it’s doing to your signal. It is drastically increasing the signal from your background, causing nasty gradients and crushing target contrast. Your best bet with a full moon in your case, since you aren’t shooting mono, would likely be to try shooting opposite the moon, and on a bright target. Go for clusters on moonlit nights, even shoot the moon if you like.


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