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Imaging during nautical darkness

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#1 nyx

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Posted 23 May 2020 - 05:34 AM

So, summer is around the corner in Germany and this is what's on the menu for me:

 

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Since this will be the first time imaging during the summer, is nautical darkness "dark enough" for astrophotography and when yes, what am I in for? Is there anything I need to adjust in my approach? I'm imaging with a ZS73 and an ASI533MC Pro.

 

Clear skies!


Edited by nyx, 23 May 2020 - 05:35 AM.


#2 gatsbyiv

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Posted 23 May 2020 - 05:49 AM

The best data I've seen on this is F. Patat et al.: "UBVRI twilight sky brightness at ESO-Paranal" in Astronomy & Astrophysics April 2006.  (DOI: 10.1051/0004-6361:20064992).  They measured the actual sky brightness in the UVBRI bands and plotted against the sun's altitude.  It is pretty clear from the charts that, at least in Chile, once the sun was 14 or 15 degrees below the horizon, it did not get any darker.  At 12 degrees (the beginning of nautical twilight), it was about 2 magnitudes brighter than the darkest level, though.  So the answer is that it's probably fully dark somewhere in the middle of nautical twilight.

 

All that said, with narrowband filters, you can effectively make it dark even earlier if you're imaging emission nebulae.  


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#3 nyx

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Posted 23 May 2020 - 06:11 AM

I am doing no narrowband imaging. I like to keep it simple with my OSC :)

#4 nyx

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Posted 24 May 2020 - 04:09 AM

So, is it worth imaging when all you have is nautical darkness?

#5 DrGomer

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Posted 24 May 2020 - 08:18 AM

Sure.  Integration times will just increase for equivalent SN. Stick to brighter targets to make it easier.  



#6 ks__observer

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Posted 24 May 2020 - 08:35 AM

You can try a dual band narrowband filter designed for OSC.


Edited by ks__observer, 24 May 2020 - 08:53 AM.


#7 ks__observer

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Posted 24 May 2020 - 08:57 AM

The best data I've seen on this is F. Patat et al.: "UBVRI twilight sky brightness at ESO-Paranal" in Astronomy & Astrophysics April 2006.  (DOI: 10.1051/0004-6361:20064992).  They measured the actual sky brightness in the UVBRI bands and plotted against the sun's altitude.  It is pretty clear from the charts that, at least in Chile, once the sun was 14 or 15 degrees below the horizon, it did not get any darker.  At 12 degrees (the beginning of nautical twilight), it was about 2 magnitudes brighter than the darkest level, though.  So the answer is that it's probably fully dark somewhere in the middle of nautical twilight.

 

All that said, with narrowband filters, you can effectively make it dark even earlier if you're imaging emission nebulae.  

I think you can easily run your own tests.

You can easily check your pixel stats for average ADU and see how it varies across time.

Even during darkness there are sometimes jumps due to transparency and local lights.

I was with a friend a while back and it was around 12am and he noticed a drop in ADU and sure enough we confirmed it with my SQM meter.




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