Question on night quality / astronomic dawn


Just one question on which darkness level or night quality is still appropriate for an amateur in Bortle class 5. What I mean is… I live a little in the north. If I would shoot M92 this night, the planning tool in the target section of SGP suggests that I have “night” from 12pm until 3 am. However, I have different IOS apps, e.g. Daylight.One, which tell me that it is not “perfectly” getting dark at my place, and that I am actually stuck in astronomic dawn until end of July.

So, the question is now what to do. Should I trust SGP or do I need to consider astronomic dawn and wait until end of July. Is astronomic dawn relevant when living in a Bortle class 5 region for someone who has slightly advanced DS astrophotography skills? I raeally would like to go on shooting :slight_smile:

Would be great to get some comments.

All the best

Take your shots and see how it goes. If they’re good enough for you, then SGP is correct. If not, then the others might be. I’m guessing that in Bortle 5 skies, astronomical twilight is irrelevant. BTW, the standard definition of “astronomical twilight” is when the sun gets more than 15 deg below the horizon.

Hi! Thank you very much.This is a good point. From what I have seen in my subframes, I would say, that it at least does not make such a big difference at exposure times of one minute. But I cannot estimate what is the effect for longer exposures and in the final stretched image.

Would be nice to know how others trust the possible start and end times proposed by SGP?

All the best

Here’s my 2-cents worth:

First off, make no mistake about it… I love SGP and can’t imagine working without it. As the author of a book on SGP Alex McConahay says, SGP allows you to Catch the Photons while Catching Your ZZZZZ’s!

First, I suspect that archer1960 is spot on with his observation about it not making much difference in your case due to light pollution. As for the times, I have no idea how SGP calculates the beginning and end of astronomical darkness, but I can tell you that the times are significantly different than times I have found elsewhere. For instance, SGP calculates the beginning of “Dusk” for my location tonight to occur at 10:07. Other apps I use predict times much closer to 10:24. For my dark site, I go with the more conservative estimates. The discrepancies exist for morning times as well.

Now let’s talk about moonrise and moonset times and let’s assume you are setting SGP’s evening tasks up before dark. The moon rise and moonset times in the planning tool appear to be very good as long as they both occur on the same date. But I have found that in the case of moonset after midnight, the time that SGP predicts is actually for the day before. In other words, it gives you the moonset for the same day in which you are setting up the sequences. The exact same problem applies to moonrise times as well. So again, I set up my times using other resources.

Who knows? I may be doing something wrong. Regardless, I love SGP and in my opinion, it is a tremendous value for the price they charge.


Thank you! This was helpful.
By the way… I also love SGP :slight_smile: