Bortle number - need help

[Flame Nebula]

This is something I've never really looked into before, but will be important for dso AP

So, do any of you have any easy ways to go outside, and determine the bortle number of your sky? 

I've looked at several websites, downloaded a couple of apps, but I suspect many of you guys can give me some good practical ways to determine it. 

Depending on how light polluted my sky is, will potentially influence what type of imaging route I take. Colour or mono. The latter being much more expensive from what I can see. 

Of course, if any of you have experience of imaging in light polluted skies with colour cameras and lp filters, please tell me. 

Based on what I've read on different sites, my sky could be anywhere from 4 to 7! I feel I need some advice. 

I live on outskirts of Nottingham, if that helps. 

Thanks 

Mark 

 

[fwm891]

If you go to the info page on FLO's website you'l find Clearoutside 'a weather' prediction ap enter your postcode for location and it will give you your bortle number. There are other programs around but that is the simplest.

[Flame Nebula]

15 minutes ago, fwm891 said:

If you go to the info page on FLO's website you'l find Clearoutside 'a weather' prediction ap enter your postcode for location and it will give you your bortle number. There are other programs around but that is the simplest.

Thanks! 🙂

[Flame Nebula]

18 minutes ago, Flame Nebula said:

Thanks! 🙂

The app is incompatible with my phone. The app must be using older version of Android or be ios only. I have a Samsung galaxy ultra with latest Android version, so it must be some other reason. 

Edit: apparently I've found other people who say it no longer works when they upgraded to a Samsung S24. Same as my phone. 🤔

Anyway, not to be easily beaten, I expected a browser version, and voila! 🙂

My skies are shown as bortle 6, which seems about right, based on other references. 

I hope this is dark enough to use normal colour cameras. 

Edited April 3 by Flame Nebula

[ONIKKINEN]

I have found this to be somewhat accurate: https://www.lightpollutionmap.info

But for the actual measurement i use ASTAP and its SQM measurement tool. You only have to take a single subexposure, calibrate it, and then run the tool on it. Astap will then make an objective measurement on your sky quality and spit out a number in magnitudes per arc second squared (SQM). I would encourage you to do this actual measurement instead of trusting what some site says, because there can be quite a bit of local variation in conditions depending on how close the nearest light source to you is.

3 minutes ago, Flame Nebula said:

My skies are shown as bortle 6, which seems about right, based on other references. 

I hope this is dark enough to use normal colour cameras. 

Sure is, broadband will take a while but nothing you can do about that. Narrowband with a duoband filter of some kind is also possible and not at all ruined by the light pollution.

[Flame Nebula]

1 minute ago, ONIKKINEN said:

I have found this to be somewhat accurate: https://www.lightpollutionmap.info

But for the actual measurement i use ASTAP and its SQM measurement tool. You only have to take a single subexposure, calibrate it, and then run the tool on it. Astap will then make an objective measurement on your sky quality and spit out a number in magnitudes per arc second squared (SQM). I would encourage you to do this actual measurement instead of trusting what some site says, because there can be quite a bit of local variation in conditions depending on how close the nearest light source to you is.

Sure is, broadband will take a while but nothing you can do about that. Narrowband with a duoband filter of some kind is also possible and not at all ruined by the light pollution.

Thanks, 

Yes, that sounds like a good idea. Preferably done at new moon and when days are shorter? 

[Flame Nebula]

3 minutes ago, ONIKKINEN said:

I have found this to be somewhat accurate: https://www.lightpollutionmap.info

But for the actual measurement i use ASTAP and its SQM measurement tool. You only have to take a single subexposure, calibrate it, and then run the tool on it. Astap will then make an objective measurement on your sky quality and spit out a number in magnitudes per arc second squared (SQM). I would encourage you to do this actual measurement instead of trusting what some site says, because there can be quite a bit of local variation in conditions depending on how close the nearest light source to you is.

Sure is, broadband will take a while but nothing you can do about that. Narrowband with a duoband filter of some kind is also possible and not at all ruined by the light pollution.

Do you have experience of how exposure time and number of exposures are affected by changing bortles? Or know of a link to such info? 

[Flame Nebula]

8 minutes ago, ONIKKINEN said:

I have found this to be somewhat accurate: https://www.lightpollutionmap.info

But for the actual measurement i use ASTAP and its SQM measurement tool. You only have to take a single subexposure, calibrate it, and then run the tool on it. Astap will then make an objective measurement on your sky quality and spit out a number in magnitudes per arc second squared (SQM). I would encourage you to do this actual measurement instead of trusting what some site says, because there can be quite a bit of local variation in conditions depending on how close the nearest light source to you is.

Sure is, broadband will take a while but nothing you can do about that. Narrowband with a duoband filter of some kind is also possible and not at all ruined by the light pollution.

So, the light pollution map also indicates bortle 6.

[Elp]

It's not just bortle zone or sky transparency that can determine your imaging conditions, local light sources are far more affecting I find. I'm bortle 7 and right next to the garden wall (east) is an LED lamppost, so therefore going all down the street north and south are more LED lampposts. The impact of this is targets rising from east or south are not really possible until I have around a 1 hour window or if they're sufficient in altitude (more than 50-60 degrees) in order to image them. Even if my scopes+dew shields do not have any stray light within the FOV if there's a lamppost nearby you can be sure they'll cast an RGB gradient across my images. As a result I rarely image RGB, it's possible but targets have to be near vertical to get "clean" images which can be stretched hard. Even with a strong LP filter like an Optolong lextreme the issue of stray light becomes worse, green/red patterns across the image. It's not just limited to camera model, I've used at least half a dozen different ones and they all suffer the same fate. From a dark site I don't get this issue.

That's why I primarily image narrowband. It's more expensive, but faster and far more flexible.

But only you can assess your immediate imaging environment and decide accordingly.

[Albir phil]

Really unless you are willing to travel to a dark site we are stuck with whatever Bortel we have, whether it's 2 or 8.

[ONIKKINEN]

1 hour ago, Flame Nebula said:

Thanks, 

Yes, that sounds like a good idea. Preferably done at new moon and when days are shorter? 

You can do this measurement at any time, you just get a different result. If you want to know what is the darkest possible sky for your location then obviously choose a night without the Moon and a target towards the zenith. Do note that you get different readings from different parts of the sky, but this is normal. Its also why its kind of pointless to declare a site "bortle 6" if one part of the sky is 7 and another is 5.

Exposure time is not so important, just a single subexposure that shows a good amount of stars (a minute or two).