How long before moonrise/after moonset?

[BrendanC]

I've been obsessing a bit lately with moon phases, rise times, set times etc, because it has such a huge impact on astrophotography.

Given that the sky gets lighter at least an hour or so before sunrise, and similarly darker after sunset, I'd imagine something similar happens with moonrise and set, albeit a lot less pronounced.

https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/how-does-the-moons-phase-affect-the-skyglow-of-any-given-location-and-how-many-days-before-or-after-a-new-moon-is-a-dark-site-not-compromised/ - short but technical and states that up to 50% moon won't have much effect if it's on the other side of the sky.

https://www.cloudynights.com/topic/511680-how-soon-before-the-moon-rises-does-the-sky-brighten/ - more anecdotal, but implies that there will be an effect up to 90 minutes before the moon rises.

Any opinions/informed guesses/facts?

Thanks, Brendan

 

 

[vlaiv]

We can argue that exposure under the full moon is better than no exposure at all and hence all the discussion about avoiding the moon is moot point.

However, this requires use of sophisticated stacking algorithm that can take into account different SNR of each subs (and no, I don't mean simple weighting available in PI ) - and such algorithm is not readily available.

I personally don't stress about moon until it shows above horizon as that coincides with visible brightening of the sky (if moon is over about 50% of illumination).

If you want to be more pedantic about all of that - get yourself SQM meter (directional one), and do measurements of your sky - with / without the moon, just before moonrise and just after moonset. This will also help you asses sky brightness N degrees away from full moon / or different phases (quarter moon and so on).

As a rough guide - two magnitudes of difference in sky brightness is equal to roughly x6 exposure time for faint stuff, but you can use SNR calculator to get the idea what is equivalent imaging time under different conditions depending on your gear and target brightness.