Bortle?

[Ags]

18 hours ago, Sunshine said:

I introduce the Milky Way visibility scale.

I haven't seen the Milky Way in years. Bortle at least further classifies the awful skies with further detail. 

[Mr Spock]

I think one requires a bortle of gin for the British weather.

[badhex]

33 minutes ago, Ags said:

I haven't seen the Milky Way in years. Bortle at least further classifies the awful skies with further detail. 

Spoken like a true Bortle Eighter 😂 I feel your pain! 😭

[Ags]

Forget Bortle 8, my area's gone to Bortle 11! 🤣

Lets show Bortle some love - it made estimating sky quality more accessible to many people. I am coincidentally working on indicative Bortle charts for a book I am writing. I don't cover Bortle 1 skies because those are just a myth, a tall tale told to gullible newbies at star parties!

Edited December 18, 2021 by Ags

[markse68]

yep i can just about make out polaris most nights but I have to know where i’m looking

[vlaiv]

1 minute ago, markse68 said:

yep i can just about make out polaris most nights but I have to know where i’m looking

I can't find it either if I'm looking in wrong direction!

[Ags]

I always know exacly where Polaris is, but it takes a minute to pick it out from the light pollution.

[jetstream]

4 hours ago, Ags said:

I am coincidentally working on indicative Bortle charts for a book I am writing.

Where did you get the reference information for these charts? ie Bortle # to NELM?

[ollypenrice]

I'm sure that if we could find the right vocalist on SGL we could make our fortune with an adaptation of a this 1962 classic. We'd call it, 'She taught me how to Bortle.' That is, if Bortling is indeed considered vocal...

Olly

[Ags]

Bortle is partly  related to NELM - each step on the Bortle scale is nominally half a magnitude of NELM.

[vlaiv]

2 minutes ago, jetstream said:

Where did you get the reference information for these charts? ie Bortle # to NELM?

I always thought that this is relevant:

[Ags]

Is the Bortle scale related in any way to the Chortle scale of humor? For example, a Chortle 1 quip can make Spock laugh.

Edited December 18, 2021 by Ags

[vlaiv]

Just to add to above post - not sure if that chart is actually true.

I've been able to spot MW at zenith - extremely faint and barely noticeable as different shading of the sky - from Bortle 8 location - edge of white / red zone, and SQM 18.5 according to Lightpollutionmap.info

According to above - it should be invisible

[Stu]

1 minute ago, vlaiv said:

Just to add to above post - not sure if that chart is actually true.

I've been able to spot MW at zenith - extremely faint and barely noticeable as different shading of the sky - from Bortle 8 location - edge of white / red zone, and SQM 18.5 according to Lightpollutionmap.info

According to above - it should be invisible

I think you must have bionic eyes then Vlad 😉. I never spotted it fro mag 18.5 skies, and got vague hints at mag 19 when the transparency was excellent.

[vlaiv]

I was also able to spot M31 from same location in good conditions using averted vision.

This seems a bit more accurate comparison table:

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

 

[jetstream]

11 minutes ago, vlaiv said:

always thought that this is relevant:

Your chart mirrors my experience, I did more observations recently using the emerging moon as a light source, which might not be a "true" LP source.  However the difference between 20.5mag and 21 is very significant and is a crossover point both in the appearance of the MW and also DSO presentation. Anything over 21 is excellent but every bit over 21 makes a big difference as well. ie the difference from 21.5 mag to 21.9 mag (my very best) is significant.

In years gone by I would travel up logging roads to observe, many many miles from anything bringing the sqm-l along to check. The results from multiple locations, offering the same sky quality all said the same thing which your chart reflects IMHO. Transparency is a key factor in all this.

Edited December 18, 2021 by jetstream

[vlaiv]

1 minute ago, Stu said:

I think you must have bionic eyes then Vlad 😉. I never spotted it fro mag 18.5 skies, and got vague hints at mag 19 when the transparency was excellent.

I guess it is down to transparency and SQM reading from lightpollutionmap.info is questionable at best. It can vary by 0.2 or more on SQM scale - depending on factors.

According to above wiki link - MW is nearly or totally invisible in 18.38–18.94, and that is my experience - on most nights one would not be able to see it, but on some nights, yes, there were hints of it - I could clearly make out direction in which it was going across the sky for example.

[jetstream]

5 minutes ago, Stu said:

I never spotted it fro mag 18.5 skies, and got vague hints at mag 19 when the transparency was excellent

Exactly my experience Stu, when I lived in town and was defining the edges of its dome.

[maw lod qan]

Polaris is all I can see in Ursa minor, but it is low and in the direction of Orlando and Disneyland. 

Back to my West, it's terrible till you get up above 45° at least.

On a really clear cool night the Milkyway is decent, but nothing like I remember as a child in the 60's.

Looking at the maps, I'm in a Bortle 3 or 4.

 

[jetstream]

This all points to one thing- if you cant see the Milky Way well you wont see DSO well either. Once DSO are seen from truly dark skies any former notion of them being "good" (as seen from lighter skies) is thrown into the garbage can.

[vlaiv]

4 minutes ago, maw lod qan said:

On a really clear cool night the Milkyway is decent, but nothing like I remember as a child in the 60's.

"In order to provide normative data on light sensitivity as a function of age and sex, some 17,500 Ss, ages 16 to 92, were tested for both form recognition ability and glare recovery time under scotopic levels of illumination. The results show: (a) a progressive deterioration of performance on both tests with increasing age, (b) a very low correlation between form recognition ability and glare recovery time, and (c) no consistent difference in performance between males and females"

https://journals.sagepub.com/doi/abs/10.2466/pms.1967.24.3c.1279?journalCode=pmsb

As we get older - we are less sensitive to low levels of light.

I guess MW looks the best to young people.

[jetstream]

14 minutes ago, vlaiv said:

I guess MW looks the best to young people.

It depends on the individual IMHO. I also believe that repeated dark viewing can enhance ones ability to see in the dark, no evidence just my thoughts. When discussing NELM the observers eyes are the wild card.

In my own case Umi 17 is a very common star in Umi I use for NELM which Simbad gives a V mag of 6.88 and Stellarium 7.1 adjusted for airmass at my location. This takes vg skies to see at least for me and the readings needed on the SQM are in the 21.7 mag+ range with super transparency.

Regardless of ones eyes, Bortle # , SQM , NELM or anything else- if the individual using his own eyes () can see the MW as bright and sharp he/she will also see DSO well through a scope.

The problem is seeing the MW at its best, at least once for a point of reference IMHO.

Edited December 18, 2021 by jetstream

[Kon]

I have been reading these thread with a lot of interest. In my limited experience as an observer, my best DSO seeing has been when the MW arch is clearly visible with structure from my observing location. I have also noted when transparency is not great, from the same location, the MW is much fainter and DSO seeing does suffer as we all know. Similarly, my SSW of the arch is not very well visible (distant LP) and DSO seeing is pretty challenging with the need of filters in a few cases. I am also guilty of using the bortle scale in my posts but going closer to village lights etc the MW is hardly visible. I agree with the previous posts that maybe a MW visibility scale is a better guideline for beginners?

[MercianDabbler]

I generally take a look on Clear Outside when choosing between potential holiday lets during spring and autumn. Bortle-wise I've noticed that it almost invariably says '4' - the same for a place we stayed on farm near Constantine in Cornwall - pretty much in the middle of nowhere and really dark and another place near Catterick where we were within a mile or two of the town and the army barracks.

I generally look at the limiting mag and sky brightness numbers now - they seem a better way to differentiate rural sites that are somewhat dark from can't see your hand in front of your face dark.

[Ags]

1 hour ago, jetstream said:

Where did you get the reference information for these charts? ie Bortle # to NELM?

It is from the original article and also wikipedia.