17 replies to this topic

[skybsd]

Hi,
Does anyone know of a resource that includes the Bortle Scale with corresponding real life images that illustrates each of the 9 levels of the Bortle Scale?

Thanks.

Regards,

skybsd

[Tony Flanders]

Does anyone know of a resource that includes the Bortle Scale with corresponding real life images that illustrate each of the 9 levels of the Bortle Scale?

I'm not sure what you mean by "real life images," but I suspect that what you want is impossible.

Do you mean images of the ground or the sky?

Do you realize that cameras pick up stars many magnitudes fainter than the eye can see? That the color of light pollution is totally different on film from to the eye?

I have taken many photos at many different levels of light pollution, but it takes pretty aggressive image manipulation to make them look anything at all like what the eye sees. And are they then really "real life images?"

[Astrojensen]

The Bortle scale, while on the surface seeming like a great idea is nothing else than a very rough guideline. I consider it basically useless. The problem is that not two observing sites are alike and one that from its description in the Bortle scale should sound like not being so good at all could in fact be superb.

What is not taken into consideration is that high-altitude locations can have a superb transparency and show very faint stars to the naked eye even if considerable light pollution is nearby, while a completely rural and pristine location near sea level can have very varying degrees of transparency even on a seemingly perfectly dark night and thus not show stars nearly as faint. Water vapor in the lower atmosphere is a big killer of transparency. It also hugely increases the impact of light pollution. Stars near the horizon also suffer incredibly, even if the sky above an altitude of 30 degrees is superb. Here on Bornholm, nearly all streetlights are turned off after midnight on workdays and houses here have no security lights and people turn off their outdoor light when they go to bed to save energy. Thus the sky over Bornholm is near pristine on many nights, yet transparency will vary tremendously and one night can be ho-hum mag 5.5 (Bortle class 6), while the next can be 7.2 (Class 2) with identical light pollution. Even from my best observing sites here it is rare to see fainter than 6.5 though there is basically no light pollution, simply because the transparency suffer from all the water vapor.

But on those rare nights of dry air, lights turned off...


Clear skies!
Thomas, Denmark

[skybsd]

Hi Tony,
Good to hear from you..,

Note that I'm merely asking the question as to whether or not anyone knows whether or not such a resource exists, okay?

Does anyone know of a resource that includes the Bortle Scale with corresponding real life images that illustrates each of the 9 levels of the Bortle Scale?

I'm not sure what you mean by "real life images," but I suspect that what you want is impossible.

Do you mean images of the ground or the sky?

Well.., yes to be honest.

In my mind's eye, what I thought was a collection of 9 |(or more, as required) photograph sequences, preferably of the same examples used in the original Bortle Scale document.

That is to say, for each Bortle Scale Level, a corresponding location is selected and photographs of the object(s) used in the original document is provided to illustrate to the reader what it is that they can expect to see.

Do you realize that cameras pick up stars many magnitudes fainter than the eye can see? That the color of light pollution is totally different on film from to the eye?

Yes - indeed I am also aware that image & graphics data processing is a rabbit hole in itself that's best left for another discussion..,

But yes, I have a fair understanding of the parameters involved

I have taken many photos at many different levels of light pollution, but it takes pretty aggressive image manipulation to make them look anything at all like what the eye sees. And are they then really "real life images?"

I believe I see your struggle. Would it help if I were to refine the definition of "real life" further, then?

How about:

"Real life" being translated to "a generated image that reflects what is seen by the eye"? Would that help?

The above refinement hopefully clarifies what I had in mind. So if someone had done this, I would expect that their approach would have been focused on the objective of just illustrating what one can expect to see via a series of corresponding photographs.

Does that make sense?

Thanks, Tony.

Regards,

skybsd

[Tony Flanders]

I would expect that their approach would have been focused on the objective of just illustrating what one can expect to see via a series of corresponding photographs.

Sketches would probably do the job better than photographs, which are notoriously poor at capturing anything even vaguely similar to what the eye sees.

It's a fair bet that nobody has done anything like this. Truth be told, one of the big problems with the Bortle Scale is that few people have a real understanding of each of the different classes.

For the record, I'm attaching a mosaic I made for an article in the Feb 2009 issue of Sky & Telescope. The left frame is from the yellow zone (green according to the snow-corrected Atlas), center from the reg/orange boundary (orange according to corrected Atlas), and right in the white zone. The top shots were all done with identical exposures (30 seconds, f/3.5, ISO 1600). The bottom shots were processed to approximate my visual impression.

Attached Thumbnails

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[Mentor]

That bottom row looks very accurate, to my eye. Nicely done!

[skybsd]

Hi Tony,
Glad you got back..,

Before I start gushing.., can you let me know your impressions of how "well matched" the bottom row is as an illustration of what you were seeing with your eyes, please?

Thanks!

Regards,

skybsd

[Tony Flanders]

Can you let me know your impressions of how "well matched" the bottom row is as an illustration of what you were seeing with your eyes, please?

No, not really. It's a subjective thing. I could look at the exact same scene a half dozen times and get a half dozen different impressions. There is no "true" picture of what the sky looks like -- or anything else, for that matter. That's why photography is an art!

Incidentally, the fact that these were all along the horizon emphasizes the differences between the locations. Shots at the zenith show subtler differences.

[skybsd]

Hi Tony,
Thanks for your thoughts.., I appreciate the challenge.

Remember though, the goal here is an illustration - yeah? The point of such an exercise is still to try to display to a reader what the objects (not really the "vista") used in the Bortle Scale descriptions for each level would "look like" at corresponding locations..,

Of course, if there is too much disparity between close to the horizon and at Zenith, then it may be a pragmatic decision to "simply" select a corresponding Bortle Scale level location where the object is higher in the night sky.

That is to say - Its almost certain that there are Bortle Scale Level "x" locations at 50°N as well as at 30°N

Many thanks..,

Regards,

skybsd

[blb]

I do not remember where I copyed this from on the web. It may have been from Tony's S&T article, Just not sure any more. Any way it may help. I hope it does.

Attached Thumbnails

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[blb]

Hey Tony,
Your bottom row picture on the right, from the white zone, looks very similar to my white zone sky. Great job, thanks

[skybsd]

Hi Buddy,
Good to hear from you..,

Yes - this is very similar to my question.., Except of course that we'd be using the objects used in the Bortle Scale for each image..,

Regards,

skybsd

[Tony Flanders]

The point of such an exercise is still to try to display to a reader what the objects (not really the "vista") used in the Bortle Scale descriptions for each level would "look like" at corresponding locations.

Here's my take. It's an almost impossible challenge to do that for one object through one telescope for one observer at one location. Photos start out looking wildly different from what one sees through the eyepiece, and its profoundly difficult to degrade them to the point where there's any resemblance at all. It's a fine art practiced by few, because most experts in photoprocessing want to make the photos look better, not worse.

Moreover, how can one capture on paper or a computer screen the experience of seeing something with averted vision? Yet averted vision is 95% of deep-sky observing.

Anyway, take that challenge, and now multiply it by 9 different light-pollution levels, coming up with a series of photos each obviously different from the next yet all comparable on the same scale. Then multiply it by 5 or 10 to get a representative sample of objects. I'll let you pick a single telescope as a standard, else you'd have to multiply it by 5 again.

Want to take on the challenge? If you succeed, you will be doing the astro world a great service. Report back on your progress every 5 years.

[blb]

That image displayes how Bortle 1, 3, 5, 7, and 9 skies compare to each other. If it does not work for you, oh well, I was hopping it would. I do not think that you will get any photo's that are any better than what Tony has provided.

[blb]

...Remember though, the goal here is an illustration - yeah? The point of such an exercise is still to try to display to a reader what the objects (not really the "vista") used in the Bortle Scale descriptions for each level would "look like" at corresponding locations..,

That would be great to have, but I have NEVER seen any thing like that for the comparison of an object in each class of sky. I agree that it would really be nice to have, but you must remember that each class simply covers a range of sky brightness. There isn't a clear break between each class.

[skybsd]

Hi Tony,

The point of such an exercise is still to try to display to a reader what the objects (not really the "vista") used in the Bortle Scale descriptions for each level would "look like" at corresponding locations.

Here's my take. It's an almost impossible challenge to do that for one object through one telescope for one observer at one location.

"Telescope"???? "Eyepiece"???

I'm no "photographer" and forgive me if I've hugely misunderstood the Bortle Scale document, but doesn't the document aim to provide the reader with a means to determine the state of their skies by looking at their skies using their eyes?

What I'm talking about is for instance..,

Let's say I have what generally matches what is defined by the Bortle Scale as "7". This level includes descriptions such as:
"Milky Way invisible; M31 and M44 may be glimpsed with the naked eye, but are very indistinct; clouds are brightly lit." And "the brightest Messier objects are only ghosts of their true selves".

So in the context of what I'm asking for, what I'd want to do is take photos of those objects used in describing what one can expect to see with their eyes

The next step would need a person (me? someone else?) who is in a Bortle Scale Level "6" to do the same for the objects used in describing this level:
"Milky Way only visible near the zenith" and "M31 is modestly apparent to the unaided eye".

Make sense? Again, I don't pretend to know the practicalities of what's needed in order to generate such images, so do let me know if I've got it all wrong, okay?

Photos start out looking wildly different from what one sees through the eyepiece, and its profoundly difficult to degrade them to the point where there's any resemblance at all. It's a fine art practiced by few, because most experts in photoprocessing want to make the photos look better, not worse.

I'm thinking (hoping?) that perhaps if we start with the goal being to generate a representation of what is apparent to the naked eye, the challenge becomes more achievable - in that the we do not expect spectacular images of the objects for the simple fact that from the naked eye vantage point, this is not what is observed

Moreover, how can one capture on paper or a computer screen the experience of seeing something with averted vision? Yet averted vision is 95% of deep-sky observing.

Anyway, take that challenge, and now multiply it by 9 different light-pollution levels, coming up with a series of photos each obviously different from the next yet all comparable on the same scale. Then multiply it by 5 or 10 to get a representative sample of objects. I'll let you pick a single telescope as a standard, else you'd have to multiply it by 5 again.

Want to take on the challenge? If you succeed, you will be doing the astro world a great service. Report back on your progress every 5 years.

I fear I may have somehow set the bar a little high here I'm only after a resource that can aid the uninitiated in having a practical way to "see" what the Bortle Scale is referring to.

As such, there's no real need to standardize on the equipment used to generate the resulting images for each level - what is important is the fact that each Bortle Scale Level's image set is only supposed to illustrate what one can expect to see. As long as any one image of the related object "looks like" what description says, its good enough - regardless of how the image was generated.

It did dawn on me that this resource may well not exist, and actually toyed with the idea of using my air-miles for something other than "sitting on a beach"

I'll have a think and try to see what I can do to kick start a project - I'm sure others will be happy to help - as long as expectations are managed, it just might work.., and maybe won't take five years - I think

Maybe I should start by finding all those camera manuals I have lying around soon!

Thanks so much its been quite informative.,

Regards,

skybsd

[Ken....]

How about using a planetarium program and adjusting the magnitude level of stars/objects displayed to match that of each of the Bortle LMs to get an idea of what things would look like? May not work well for gradations of extended objects though.

[skybsd]

Hi Ken,
Good to hear from you..,

Yes, I've tried a couple (of the free ones), and they do make a decent job of it.

I'll spend some time thinking some more on this though..,

Thanks!

Regards,

skybsd