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Effects of increasing moon, decreasing darkness and descending target over 4 consecutive nights

Acquisition Processing H-alpha Deep Sky
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Christian Bennich avatar
Christian Bennich avatar
I was processing some Ha data collected over the last 4 very short "nights" in Denmark. 
Over the 4 nights, seeing expressed in FWHM - between 2,5"-3,7" and my guiding has been steady between 0,5"-0,6".

No other changes to my setup etc. was made. 
Only "change" has been the increasing moon and the nights getting shorter, and the target setting on the nightsky. 

I think it's a fun observation. 

Tobiasz avatar
Tobiasz avatar
Interesting. Thanks for sharing.
Kay Ogetay avatar
Kay Ogetay avatar
Interesting observation, thanks for sharing. But I have questions, sorry for being too nit-picky about the science, I'm just curious. First, how does this x-axis (n-th image) translate into day/time? I'd like to see a second x-axis that shows the position of the Moon (or distance to the Moon). Another factor that would affect the FWHM of stars is the angular position of the object you are imaging. If it decreases over the night (more atmospheric disturbance), how do we know it is not the main factor but the Moon is?
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Christian Bennich avatar
Christian Bennich avatar
Kay Ogetay:
Interesting observation, thanks for sharing. But I have questions, sorry for being too nit-picky about the science, I'm just curious. First, how does this x-axis (n-th image) translate into day/time? I'd like to see a second x-axis that shows the position of the Moon (or distance to the Moon). Another factor that would affect the FWHM of stars is the angular position of the object you are imaging. If it decreases over the night (more atmospheric disturbance), how do we know it is not the main factor but the Moon is?

@Kay Ogetay 🤪 - good questions. 
I was imaging Abell1656 - The Coma Cluster.
I am near Copenhagen in DK.  
Starting at Nautical Dusk and ending at Nautical Dawn - which is now 02:43 - when imaging it was slightly later. 

Data was acquired on May 12-15. 

As I wrote in my original post, I testament the degradation in image quality to a combination of Moon, the targets angular position and just generally shorter nights.
Kay Ogetay avatar
Kay Ogetay avatar
Christian Bennich:
Kay Ogetay:
Interesting observation, thanks for sharing. But I have questions, sorry for being too nit-picky about the science, I'm just curious. First, how does this x-axis (n-th image) translate into day/time? I'd like to see a second x-axis that shows the position of the Moon (or distance to the Moon). Another factor that would affect the FWHM of stars is the angular position of the object you are imaging. If it decreases over the night (more atmospheric disturbance), how do we know it is not the main factor but the Moon is?

@Kay Ogetay 🤪 - good questions. 
I was imaging Abell1656 - The Coma Cluster.
I am near Copenhagen in DK.  
Starting at Nautical Dusk and ending at Nautical Dawn - which is now 02:43 - when imaging it was slightly later. 

Data was acquired on May 12-15. 

As I wrote in my original post, I testament the degradation in image quality to a combination of Moon, the targets angular position and just generally shorter nights.

Thanks for the details! You definitely instigated some thoughts Now I want to do my own test like this to see how it changes!
IrishAstro4484 avatar
IrishAstro4484 avatar
Christian Bennich:
I was processing some Ha data collected over the last 4 very short "nights" in Denmark. 
Over the 4 nights, seeing expressed in FWHM - between 2,5"-3,7" and my guiding has been steady between 0,5"-0,6".

No other changes to my setup etc. was made. 
Only "change" has been the increasing moon and the nights getting shorter, and the target setting on the nightsky. 

I think it's a fun observation. 


*** Silly question but what is this graph actually showing?

Did you also try plot SNR over the 4 nights?***
Christian Bennich avatar
Christian Bennich avatar
Christian Bennich:
I was processing some Ha data collected over the last 4 very short "nights" in Denmark. 
Over the 4 nights, seeing expressed in FWHM - between 2,5"-3,7" and my guiding has been steady between 0,5"-0,6".

No other changes to my setup etc. was made. 
Only "change" has been the increasing moon and the nights getting shorter, and the target setting on the nightsky. 

I think it's a fun observation. 


*** Silly question but what is this graph actually showing?

Did you also try plot SNR over the 4 nights?***

The graph shows the Image Weight as processed and evaluated through NormalizeScaleGradient, which I use after WBPP to Normalize my frames.

Just for you @IrishAstro4484   - here is the relations between Weight, SNR, AirMass and Altitude of target

To make the axis-scales "work" I "scaled" down the Altitude. So e.g. 0,6 in Altitude is 60 degrees above the horizon. 

 And the excel file with the data - if relevant. 

ASTRODATA.xlsx