Is there a correlation between Bortle and brightness off of the LP maps?

[Trippelforge]

I have been making a list of camping sites via their projected darkness. I mostly stuck to simply the bortal rating of each, but then of course other measurements are presented. But from a simple standpoint I was curious if there was a brightness range that qualifies each bortal number.

For example;

Site 1: Bortal 4 @ .230 brightness
Site 2: Bortal 3 @ .190 brightness
Site 3: Bortal 2 @ .188 brightness

Does that mean that a Bortal 2 turns to a Bortal 3 at around .190? If so would that mean that the .188 site vs .190 are so close the rating is irrelevant?

Side Note: I do understand that the light pollution maps are not exact, and can be outdated. But I was just trying to get a general idea prior to driving across my state.

[drdre2030]

No expert...but the Bortal scale does use the NELM magnitude which is kind of what you are looking for I think, whilst maybe not brightness per se but is a scale. I think the difference between B2 to B1, B3 to B2 is not that big, B4 to B3 starts to make a difference, then each one after exponentially. 

I think as you say with things not being exact or outdated, trying to find reviews or people who have been to other places is probably a subjective, but informed way of trying to know if worth it.

[Trippelforge]

16 minutes ago, drdre2030 said:

No expert...but the Bortal scale does use the NELM magnitude which is kind of what you are looking for I think, whilst maybe not brightness per se but is a scale. I think the difference between B2 to B1, B3 to B2 is not that big, B4 to B3 starts to make a difference, then each one after exponentially. 

I think as you say with things not being exact or outdated, trying to find reviews or people who have been to other places is probably a subjective, but informed way of trying to know if worth it.

Someone shared a few charts with me showing the various differences in exposure times, and you are right. It's pretty mind blowing how quickly it rockets upward. 

 

[drdre2030]

1 minute ago, Trippelforge said:

Someone shared a few charts with me showing the various differences in exposure times, and you are right. It's pretty mind blowing how quickly it rockets upward. 

 

Yes that's what I saw, only in chart form!

[vlaiv]

[Floater]

Bortle.

I know it’s not spelled the way it’s spoken, but we’re talking English language - a strange language to defend. 😱

[vlaiv]

1 minute ago, Floater said:

Bortle.

I know it’s not spelled the way it’s spoken, but we’re talking English language - a strange language to defend. 😱

Btw, how is it pronounced?

[Floater]

1 hour ago, vlaiv said:

Btw, how is it pronounced?

I take your question as being tongue in cheek 👍 but that is my very point. Pronunciation and English are strange bedfellows. 

Sometimes I think ‘US English’ is a far more sensible way of spelling … and then I remember my school teachers!!

My aim is only to point out that it’s Bortle, not any other phonetical deviation. This is similar to another forum exchange a while back involving Albireo (correct) and Alberio (wrong). ‘Fraid I can’t help myself. 😑

Anyhow, sorry @Trippelforge, didn’t mean to drag this off thread.

[vlaiv]

2 minutes ago, Floater said:

I take your question as being tongue in cheek 👍 but that is my very point.

No, it was genuine question. As far as I know - it is surname, and I have no idea of how it is pronounced (never heard anyone pronounce it).
 

Anyways, I've found it online (with audio) and it is pronounced the way I imagined

[John]

I would pronounce it "Bor-tul" but spell it as @Floater suggests. 

I was surprised to learn that the scale has only been around since 2001 when John E Bortle published it in Sky & Telescope. Here is that article re-published by Sky & Telescope in 2008:

Light Pollution and Astronomy: How Dark Are Your Night Skies? - Sky & Telescope (skyandtelescope.org)

[Trippelforge]

1 minute ago, John said:

I would pronounce it "Bor-tul" but spell it as @Floater suggests. 

I was surprised to learn that the scale has only been around since 2001 when John E Bortle published it in Sky & Telescope. Here is that article re-published by Sky & Telescope in 2008:

Light Pollution and Astronomy: How Dark Are Your Night Skies? - Sky & Telescope (skyandtelescope.org)

Funny enough I don't even know anymore HOW I was saying it due to you posting that. Bortle, bortal... ugh. Now I am all messed up...

 

 

[Geoff Barnes]

I think it should be spelled "Brutal" for anyone living with the light pollution that most suffer from! 😕

[Sunshine]

I hate that word, bortle, sound like something out of the Klingon dictionary.

[drdre2030]

40 minutes ago, Sunshine said:

I hate that word, bortle, sound like something out of the Klingon dictionary.

Bor'TLE DaS! 

[bosun21]

4 hours ago, Floater said:

Bortle.

I know it’s not spelled the way it’s spoken, but we’re talking English language - a strange language to defend. 😱

It is spelt the way it's spoken to my understanding. BOR-TIL.

[Sunshine]

5 hours ago, Floater said:

English language - a strange language to defend. 😱

Example:

park on a driveway, drive on a parkway.

feet smell and a nose runs.

 

[Icesheet]

7 hours ago, Trippelforge said:

Someone shared a few charts with me showing the various differences in exposure times, and you are right. It's pretty mind blowing how quickly it rockets upward. 

 

Does anyone know the background of this table, how it is measured and how reliable it is? I was obviously aware of the hugely detrimental effect of light pollution but hadn’t really seen it set out numerically like this. That’s mind blowing to me and potentially hugely significant. According to light pollution maps I image from just inside a Bortle 4 zone. However, depending on the direction I image it can be towards B2/3 or B5/6. Given the significance of the apparent jump from 4-5, I wonder if my imaging time is better spent solely towards Bortle 4 and under. Could anyone suggest what I could do to test this?

 

Edit: Apologies, I see this is in an Observing forum. I can start a new topic in an Imaging forum if it’s preferable. 

Edited November 9, 2023 by Icesheet

[vlaiv]

9 hours ago, Icesheet said:

Does anyone know the background of this table

I think it is not universal thing.

There are multitude of factors that determine final "time to SNR".

If you want to do it for yourself, it's best to take one of SNR calculators (where you input things like target brightness, sky brightness, QE of camera, losses in telescope, aperture, focal length, pixel size, etc) which will give you SNR after certain imaging period - or required imaging time for target SNR - and you then compare results when you vary sky brightness.

I've once did that and found that moving from SQM18.5 to SQM20.5 yields time reduction of about x6.25 (which corresponds to above table as difference between sqm20 and sqm22 - so maybe it is universal thing?).

[Icesheet]

Thanks @vlaiv. So presumably I can do this with existing exposures I have that have tracked across the different Bortle zones in my area on the same night? Now that I think about it I have noticed a trend from the PixInsight subframe selector that my exposures seem to get poorer as the night progresses. I wonder if that correlates with moving to a more light polluted part of the sky. 

[bomberbaz]

20 hours ago, Trippelforge said:

Someone shared a few charts with me showing the various differences in exposure times, and you are right. It's pretty mind blowing how quickly it rockets upward. 

 

Bit of a jump from 21.59 to 20. Place I occasionally image from is 20.7 and it is doing difficult to extrapolate timings from that. That said, there is always sharpcap tool to use. 

[ONIKKINEN]

Anecdotal evidence from me, but have also found that imaging just an hour or two from an SQM 21.3 location results in a better image than any single night could (6-8h) from a 19.5-20.5 location. So i find that 6x imaging time required per 2 magnitudes is easy to believe.

[Trippelforge]

19 hours ago, Icesheet said:

Does anyone know the background of this table, how it is measured and how reliable it is? I was obviously aware of the hugely detrimental effect of light pollution but hadn’t really seen it set out numerically like this. That’s mind blowing to me and potentially hugely significant. According to light pollution maps I image from just inside a Bortle 4 zone. However, depending on the direction I image it can be towards B2/3 or B5/6. Given the significance of the apparent jump from 4-5, I wonder if my imaging time is better spent solely towards Bortle 4 and under. Could anyone suggest what I could do to test this?

 

Edit: Apologies, I see this is in an Observing forum. I can start a new topic in an Imaging forum if it’s preferable. 

It was shared on Cloudynights by a member, there was a graph as well. I believe he wrote up an entire paper outlining his methodologies (I will look for it). But he is seemingly a fairly well respected member so I just kind of went with it (lol). Anyways my mind was blown as well, I live in a bortal 5/6 zone and my son and I have been planning to go camping this winter to some 2/3 zones.  Which obviously looking at the chart is going to be insane.   

[Nigella Bryant]

I live on the edge of Bortle 4 going into Bortle 3 on the map. I can easily distinguish the milky way without averted vision yey the chart says I shouldn't be able to see it. It seems really dark at this time of year and I have to watch where I'm walking so I don't trip over walking to the dome. People use torches to walk up the road here. 

[Clarkey]

15 minutes ago, Nigella Bryant said:

People use torches to walk up the road here

I need a visor to reduce the glare🤣

[vlaiv]

1 hour ago, Nigella Bryant said:

I live on the edge of Bortle 4 going into Bortle 3 on the map. I can easily distinguish the milky way without averted vision yey the chart says I shouldn't be able to see it

I'm not sure you are reading the chart correctly?

Not only it is visible - it shows some detail.

In fact, there is detailed description of how it "feels" to be under certain Bortle sky:

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