Bortal No of my nightsky

[Dunc78]

Hello

Is there an app or how do I find out the bortal number of my local nightsky? 

Thanks 

[vlaiv]

https://www.lightpollutionmap.info

Click on the map where you want and you will get estimate for sky conditions looking like:

[Zermelo]

The Bortle scale is defined descriptively, but it is often simpler to assess in terms of a numerical sky brightness value, mapped to the Bortle scale as in the link above.

The definitions are discussed here :

https://en.m.wikipedia.org/wiki/Bortle_scale

https://skyandtelescope.org/astronomy-resources/light-pollution-and-astronomy-the-bortle-dark-sky-scale/

[Guest]

Also often times, as in my case, sky darkness varies depending on direction.  I have a very bright dome roughly southeast and another northwestish.  However west and northwest are significantly darker.

So take any LP map with a grain of salt and just as a very broad reference.

[bosun21]

The Clear Outside app provides the Bortle scale number for your area.

[Waddensky]

The Bortle scale is quite subjective and most websites use old VIIRS data to calculate the sky brightness. This website uses the most recent data I know of, from 2022. It doesn't list the Bortle scale but it has a colour legend that more or less matches the usual colours that are used for Bortle maps. 

If you want to know the actual sky brightness of your observing location, you can buy a Sky Quality Meter. I have one, nifty little devices. 

[vlaiv]

6 minutes ago, Waddensky said:

The Bortle scale is quite subjective and most websites use old VIIRS data to calculate the sky brightness. This website uses the most recent data I know of, from 2022. It doesn't list the Bortle scale but it has a colour legend that more or less matches the usual colours that are used for Bortle maps. 

If you want to know the actual sky brightness of your observing location, you can buy a Sky Quality Meter. I have one, nifty little devices. 

Very nice, but is there any way to get coordinate mapping?

As is, resolution is not good enough to pinpoint location. According to that map, I'm somewhere between 20.0 - 20.5 and 20.5-20.9 areas.

Above gives 20.84, but I'm sure that level of LP has risen from 2015, so it is more like 20-20.5 now.

[Kon]

1 minute ago, vlaiv said:

Very nice, but is there any way to get coordinate mapping?

As is, resolution is not good enough to pinpoint location. According to that map, I'm somewhere between 20.0 - 20.5 and 20.5-20.9 areas.

Above gives 20.84, but I'm sure that level of LP has risen from 2015, so it is more like 20-20.5 now.

Click on 'View Atlas in OpenStreetMap' and you can search using a postcode.

[Kon]

You are better off judging sky quality by the milky way appearance from your location. Do you see it and how bright is it?, Does it have some or fine structure? Can you see some of the fuzzies naked eye? I am blessed with dark skies (milky way is bright, with intricate structure and several objects can be seen by naked eye) and it is usually an indication of sky quality for the night; bad seeing the milky way is just there and hunting DSOs is not easy.

[vlaiv]

12 minutes ago, Kon said:

Click on 'View Atlas in OpenStreetMap' and you can search using a postcode.

I completely missed that! Thanks!

[vlaiv]

Light pollution atlas 2022 also features click for more information when opened in OpenStreetMap

I'm currently at 20.34 according to that data source (which I think is very much the case).

It also provided me with new possible observing location that I must relay to my local astronomy buddies

 

[Waddensky]

16 minutes ago, vlaiv said:

Light pollution atlas 2022 also features click for more information when opened in OpenStreetMap

I'm currently at 20.34 according to that data source (which I think is very much the case).

It also provided me with new possible observing location that I must relay to my local astronomy buddies

 

That's great! 😄

It's good to realise that the light pollution data is based on a method outlined in a paper by Cinzano et al. (link) that uses satellite data and a light propagation model to calculate the sky brightness. It's not based on actual measurements of the night sky. In my experience, the model is quite accurate though. 

[jjohnson3803]

I use a couple of LP maps online for the big picture, but use this to estimate by eye:

 

Edited February 22 by jjohnson3803

[bosun21]

4 hours ago, Kon said:

You are better off judging sky quality by the milky way appearance from your location. Do you see it and how bright is it?, Does it have some or fine structure? Can you see some of the fuzzies naked eye? I am blessed with dark skies (milky way is bright, with intricate structure and several objects can be seen by naked eye) and it is usually an indication of sky quality for the night; bad seeing the milky way is just there and hunting DSOs is not easy.

Where are you roughly located Kostas? I can only dream of a bright Milky way despite not living that far apart from each other. Thank god that planetary doesn't really require dark skies(within reason). I see you are looking for a short Cheshire on the wanted adds. Is this to align your secondary mirror and see the primary clips? I could borrow you my 2" Concenter to allow you to set your secondary mirror if you like. PM me if interested.

[Guest]

The one issue I have with the bortle scale descriptions, at least in my case, is that they depend on your eyes.  I know I have dark skies in certain directions, and m31 crosses one of them, yet I cannot see it naked eye.  I should by all accounts, since I've measured it.  My eyes are pretty bad though.  For young healthy eyes I don't think this is an issue but if your eyes are not what they used to be, keep that in mind.

I looked at the values for both maps btw against the value I got from my measurements.  Now sqm readings can vary from night to night due to transparency, but it seems both maps are fairly accurate within some margin of error.  My readings average 21.4 while the maps show 21.31 and 21.51 respectively.  Not too bad.  This is zenith of course.  Close enough to have a good idea at least.

[Kon]

2 hours ago, bosun21 said:

Where are you roughly located Kostas? I can only dream of a bright Milky way despite not living that far apart from each other. Thank god that planetary doesn't really require dark skies(within reason). I see you are looking for a short Cheshire on the wanted adds. Is this to align your secondary mirror and see the primary clips? I could borrow you my 2" Concenter to allow you to set your secondary mirror if you like. PM me if interested.

I am outside Swindon, Brinkworth, quite rural. I am at the edge of the village with only 2 neighbours and plenty of farms in between.

Thanks for the very kind offer. I bought myself a short Cheshire and I had some issues that I posted on getting starting with equipment section this morning. I think I know my problem but I might get you on the offer if I still struggle.

[bosun21]

5 minutes ago, Kon said:

I am outside Swindon, Brinkworth, quite rural. I am at the edge of the village with only 2 neighbours and plenty of farms in between.

Thanks for the very kind offer. I bought myself a short Cheshire and I had some issues that I posted on getting starting with equipment section this morning. I think I know my problem but I might get you on the offer if I still struggle.

A Concenter is the most visually accurate for getting the secondary perfectly set. It positions the secondary accurately centered in the focuser draw tube and more importantly it sets the secondary mirror tilt for all of its axes. A laser can not do this neither can a Cheshire accurately. Once I get the collimation bang on the difference is very noticeable.

[Zermelo]

11 hours ago, Waddensky said:

It doesn't list the Bortle scale but it has a colour legend that more or less matches the usual colours that are used for Bortle maps.

If anyone missed the link to the key, it's here.

My home is placed within the 20.91 - 21.25 band, probably around 21.05 - 21.10 based on the neighbouring regions. This agrees quite well with my experience - the darkest I've measured here with my meter is 21.02.

Intresting that (in the Wikipedia mapping, at any rate), anything better than 21.75 is mapped to Bortle 1. But on the Lorenz map, that range is split across five colour bands, because the bands are narrower at the top.
So, for example, the darkest parts of Exmoor National Park are claimed as Bortle 1 in their guide, and the map is not inconsistent with that, showing in the 21.69 - 21.81 band. But there are parts of Wales, and especially Scotland, that are in the darker bands.

 

Edited February 22 by Zermelo
"four colour bands" > "five colour bands"