Broadband Imaging and Moonlight

dont imaging i nthe same area as the moon.

im now only do objects in the north, because the moon is in the south.

i only use a uv/ir filter, with good flats etc its ok. there is enough good broadband objects in the north, Cepheus has much, Cygnus also.

Here in the north the sun almost not go down anymore, so broadband is limited to hours or so.

Good idea is objects like M13.

Tobiasz · May 25, 2026 at 04:43 PM

Hi,

1. Depends on the effort you have to invest to start imaging. Do you have a semi permanent setup that only has to be turned on to shoot? Then I would do it. If you’re mobile like me, it’s not worth it in my opinion.

2. Depends on your stacking program and the measurement algorithms. I throw everthing I have into PI WeightedBatchPreProcessing and let Pixinsight decide with “PSF Signal Weight”. Worse nights have less weight and therefore less impact on the stack.

Regards

little effort necessary. my setup is somewhat semi permanent.

1. still the question remains. would you maybe get a better result by not throwing all the frames in? i had an project containing only ha and oiii and a few oiii frames which included cirrus clouds have made it impossible to bring out any oiii at all.
   clouds are not moonlight though…
   

If you image in low Bortle then not worth it, as in 1h of data in low moon you will probably get better SNR than an entire night with a full moon.

If you live in Bortle 8/9 then image away, as long as your target is not too close to the moon.

Tony Gondola · May 25, 2026 at 05:37 PM

You can consider Moonlight to be another form of light pollution as it has pretty much the same effect. Now ask yourself, would you drive to a remote location with worse light pollution than you have at home? Of course you wouldn’t. If you can see the effect in your images then it’s too much. Just don’t do it. Shoot narrowband, bright lucky imaging targets, the Moon itself, anything that’s not as effected. IMO, it’s just not worth it.

Hey tony,

I can clearly see the difference between frames where cars drove by versus those without, as well as between images taken under a 20% moon and a completely dark sky. I’m confident I could even detect differences in frames captured while a funfair is running 10 km away compared to when it’s not.

Do you think adding 100h of quality lum data from bortle 7 skies to 1h of data of the same setup from bortle 1 would be a good thing? Neutral? Maybe even harmful if the goal is to bring out faint stuff?

Anderl · May 25, 2026, 05:53 PM

Tony Gondola · May 25, 2026 at 05:37 PM

You can consider Moonlight to be another form of light pollution as it has pretty much the same effect. Now ask yourself, would you drive to a remote location with worse light pollution than you have at home? Of course you wouldn’t. If you can see the effect in your images then it’s too much. Just don’t do it. Shoot narrowband, bright lucky imaging targets, the Moon itself, anything that’s not as effected. IMO, it’s just not worth it.

Hey tony,

I can clearly see the difference between frames where cars drove by versus those without, as well as between images taken under a 20% moon and a completely dark sky. I’m confident I could even detect differences in frames captured while a funfair is running 10 km away compared to when it’s not.

Do you think adding 100h of quality lum data from bortle 7 skies to 1h of data of the same setup from bortle 1 would be a good thing? Neutral? Maybe even harmful if the goal is to bring out faint stuff?

What I know is that the better the data, the better the result. I would hope that you are culling bad frames as a matter of course. In the end, it’s up to you. I don’t shoot below 60 deg. elevation, even on dark nights. It’s just the way I like to work.

There is element to this question that hasn’t been addressed. The question of “is it worth it” for broadband imagery can be answered in a semi-quantitative way. Almost all stacking algorithms will assign weights to images. The sky brightness decreases the S/N under a bright moon (the sky itself adds photon noise). If you were to take data all under the bright sky- then the data would be given nearly equal weights and the time spent acquiring the data would go into the final stacked frame in equal measure.

However, if you stack frames taken with a bright moon and under dark skies- you should ask yourself what is the weight being given to the moon data? In PixInsight you can directly see this answer. It depends on the brightness of the sky (and it does have a color dependence since the sky is blue)- but roughly (ignoring light pollution) when using the default weighting scheme (PSF Signal Weight) each moonlit image might only be worth 20% of a moonless (dark sky) image. You have to take 5 images to achieve what a single frame under dark skies gets- and this estimate might be optimistic.

This is why narrowband images- specifically red (Ha and SII)- are reasonably in the moonlight. The background sky is still quite dark. However, above still applies even to narrowband images. If you compare Ha data taken under dark night skies- it will still be assigned higher weights.

-adam