38 replies to this topic

[MEE]

moefuz wrote:
Aside from that, we have people with good eyesight that have seen stars with averted vision down to magnitude 8.1 (verified), and I once hit 7.8 from there, although I can't reach quite that level anymore….My local dark sky site isn't that good, but it isn't bad either, as it can allow me to occasionally get down to a ZLM of 6.7 to 7.1 or so on a really good night.

Is there a standard for naked eye limiting magnitude, regarding time spent and/or percentage of time seen?

One person could be at a location and be pushing his/her ZLM to the limit- spending 30+ min to see a star 10-15% of the time

Another person at the same site could be more casual and just spend 10 min and see a star 50-60% of the time and be fine with that

It’s good to have consistency

[MEE]

Frankly, I don’t give a hoot what my bortle or SQ whatever is.

Then don’t mention it.

Mention the things that don’t change first:

The color zone you’re in (and the source you used for it).
By the way, this one from Dave Lorenz is said to be more accurate: https://djlorenz.git...erlay/dark.html

What your local light pollution situation is (no interference, moderate, severe) (lights within a few miles)

Then mention the conditions for that night:

The cloud cover situation (%, thick or thin, etc)

The phase of the moon and its altitude above the horizon

How close to the horizon could you see faint stars (lots of stars sprinkled like sugar grains as opposed to only the brighter ones)- in each direction

The Milky Way: is it visible? If so, to what degree? Faint? Easy but washed out? Crisp and brilliant? How close to the horizon could you see it?

Zodiacal Light: on spring evenings, facing west, or fall predawn, facing east: can you see it? How bright is it? How far does it extend?

Guess what? Once you report your actual conditions, we can probably figure out the Bortle rating of that night

The Bortle rating will change at your location, because it’s based upon the conditions for that night

[Jon Isaacs]

This topic has been discussed extensively in the Light Pollution forum.  

 

Light Pollution Maps hijacked the Bortle ratings and in so doing, made them nearly worthless.  Bortle 4 ranges from their estimation of 21.69 mpsas to 20.50 mpsas.  That is a factor of 3 in sky brightness.  And that does not include the errors in the predictions.  I measure the sky brightness with both an SQM and an SQM-L.  The best nights, LPM under estimates the sky brightness by at least 0.3 magnitudes.  

 

Cloudy Nights member David Lorenz is an atmospheric scientist at the University of Wisconsin, Madison. He has created the Light Pollution Atlas and updates it frequently, the latest version is 2024.  It is user friendly, you can look up street addresses if you want.  There are no Bortle ratings, a good thing.  His predictions pretty much agree with what I measure with an SQM-L on a good night.

 

https://djlorenz.git...o/astronomy/lp/

 

I recommend reporting observations, either NELM, actual Bortle or SQM/SQM-L.  If you want to use a map to find new places to observe or estimate your own site's sky brightness, I recommend using the Light Pollution Atlas.

 

Jon

[Jehujones]

 

Finally figured out my Bortle!

Clickbait! 

 

 I clicked on this topic because I am always interested to hear about fellow observers using this technique and the results of their efforts. I personally have not been successful with the method because I run into conflicting descriptions of my conditions.

Instead, I clicked on another ad nauseam debate about maps 

[moefuzz]

This topic has been discussed extensively in the Light Pollution forum.  

 

Light Pollution Maps hijacked the Bortle ratings and in so doing, made them nearly worthless.  Bortle 4 ranges from their estimation of 21.69 mpsas to 20.50 mpsas.  That is a factor of 3 in sky brightness.  And that does not include the errors in the predictions.  I measure the sky brightness with both an SQM and an SQM-L.  The best nights, LPM under estimates the sky brightness by at least 0.3 magnitudes.  

 

Cloudy Nights member David Lorenz is an atmospheric scientist at the University of Wisconsin, Madison. He has created the Light Pollution Atlas and updates it frequently, the latest version is 2024.  It is user friendly, you can look up street addresses if you want.  There are no Bortle ratings, a good thing.  His predictions pretty much agree with what I measure with an SQM-L on a good night.

 

https://djlorenz.git...o/astronomy/lp/

 

I recommend reporting observations, either NELM, actual Bortle or SQM/SQM-L.  If you want to use a map to find new places to observe or estimate your own site's sky brightness, I recommend using the Light Pollution Atlas.

 

Jon

.....Speaking of maps 

 

If more people used Lorenz's map maybe we could get away from the funkyness of the Bortle system.

 Maybe Bortle served it's purpose when it was introduced but has obviously been eclipsed by newer more accurate and descriptive systems.

 

In using both (interchangeably) it only seems to add to the confusion and bring up the same old volley of replies.

 

As Jon wisely pointed out, there are better maps out there that cut all mention of Bortle thus eliminating any confusion.

 

https://djlorenz.git...o/astronomy/lp/

 

.

Edited by moefuzz, 16 June 2025 - 01:04 PM.

[David Knisely]

Is there a standard for naked eye limiting magnitude, regarding time spent and/or percentage of time seen?

One person could be at a location and be pushing his/her ZLM to the limit- spending 30+ min to see a star 10-15% of the time

Another person at the same site could be more casual and just spend 10 min and see a star 50-60% of the time and be fine with that

It’s good to have consistency

No, there is not some hard and fast "standard", although traditionally, a "dark sky" has often been considered to be where the average observer can see 6th magnitude stars with averted vision fairly consistently.  I don't spend more than just a few minutes determining my personal ZLM during a session, as it is mostly for my own use in recording my observations in my log book.  If I wanted something more scientific, I would get an SQ meter, or better yet, do telescopic photometry of a very small area of sky limited by a properly-selected diaphragm in front of the sensor.  If I ever see someone on the observing fields with a full photometry setup using a 1P21 photomultiplier tube, I would definitely get more than a little nostalgic!  .  Clear skies to you.     

[JayinUT]

I use my SQM L to record with my observations. What the SQM L doesn't tell you is overall conditions and how good to great a night is. That I belive is up to the observer to determine. If they or I go out and enjoy our time out, I think that is what matters most.

 

One thing stated in this threat that I whole heartedly agree with is that If it is clear I head out either to the backyard or to one of my favorite dark sites. I can adjust my targets based on local conditions but I still get out. It is the experience and the enjoyment of what I do in this hobby that matter most to me. I know what I WANT to observe, just like I KNOW how I anticipate and hope each day will go. I've lived long enough to know I'll take the best of what I am given and make the most of it. Works for me. 

Edited by JayinUT, 16 June 2025 - 01:04 PM.

[mountain monk]

I am fortunate to live near very dark skies--all my favored sites near home, re DaveL's map, are 21.9+ and my favorite is 21.98. I hasten to add that they are not that dark now because of solar activity. The last time I checked with my meter it was 21.89--and I won't complain. I also observe in southern Utah at sites that the map says are 22.00. They aren't that dark now, either. But because I was a mountain guide all my life, with years in the Himalayas, Central Asia, and Peru, I've seen the sky at, max, 21,000 feet, and for months over 15,000 feet. At those altitudes the sky is not darker; indeed with so many stars it seems lighter. What is different is the amazing increase in transparency. I have said that the effect is three dimensional--though no one seems to like that description. So be it. Somewhere in one of Sue French's books she quotes an early explorer who under the best conditions could see more stars than ever before--in the Pleiades?--but then soon afterwards many of them vanished. I believe that. And I hope that everyone here at times experiences the same exceptional view--it is transformative.

 

Dark, clear, calm skies.

 

Jack

[moefuzz]

  At those altitudes the sky is not darker; indeed with so many stars it seems lighter. What is different is the amazing increase in transparency. I have said that the effect is three dimensional--though no one seems to like that description. So be it. Somewhere in one of Sue French's books she quotes an early explorer who under the best conditions could see more stars than ever before--in the Pleiades?--but then soon afterwards many of them vanished. I believe that. And I hope that everyone here at times experiences the same exceptional view--it is transformative.

 

Dark, clear, calm skies.

 

Jack

I could agree that at or near 22:00 the stars seem to almost pop right out of the skies.

There's something to be said of seeing nebula (naked eye) that others have difficulty seeing in light gathering reflectors.

 

Just north of you, well a little further north of you is Grasslands National Park which edges onto the northern tip of Montana.

Grasslands is a true 22:00.

 

Grasslands is a designated dark area specifically targeted at tourism with an eye on Astronomy.

In actuality there are 2 separate large parcels totalling 350 sq miles.

The view alone from 70 mile peak is spectacular as you can often see Bison grazing far off in the distance.  And I love the prairie landscapes (having grown up in the west)

 

For us this is now a 10 hour trip to the south and east and It does make for an interesting side trip if and when I go down to the Black Hills area but I haven't been thru there for years.

 

it truly would be spectacular if Montana/USA picked up the proverbial torch and designated an adjacent patch as "designated dark area" giving Montana a second international/state park.

 

 

 

 

 

49.03655, -107.10832

 

 

 

if I recall correctly there has or had been some interest in signing an agreement with Montana in making Saskatchewan's Grasslands (Astronomy Dark) Park an International one via allotting a parcel on the US/Montana side as an adjoining Star Park.

 

 

 

 

(pics from the net)

 

 

 

 

 

Also, I'm surprised nobody had brought up the point about the seeing during sunspot lulls

so you make some excellent points

 

cheers,

moe.

 

 

.

 

[David Knisely]

moefuzz wrote:

 

Also, I'm surprised nobody had brought up the point about the seeing during sunspot lulls

so you make some excellent points.

 

Seeing is mainly dependent on the atmospheric stability and is not terribly affected by solar or sunspot activity.  I have had nights of average to poor transparency or moonlit nights where seeing was excellent (half an arc second or slightly better), so even from home with my local sky glow, I can still sometimes do nice work at high power on the moon, planets, and double stars with crisp image quality and only momentary disturbances (Antoniadi I to II level seeing).  Sky background brightness *is* affected by solar activity however, so the SQM readings tend to be somewhat worse near sunspot maximum.  Clear skies to you.

[moefuzz]

 

  Sky background brightness *is* affected by solar activity however, so the SQM readings tend to be somewhat worse near sunspot maximum. 

 

...Clear skies to you.

 

 

 

 

A few years ago we took a chance and ignored the weather forecast and headed east.

That was the exceptional night of seeing Flaming Star Nebula naked eye.

 

My philosophy is that when you are in an area that is capable of achieving perfect skies

every little bit helps.

And the difference between being under ~21:97 and 22:00 just makes the occasion even more memorable

because those days don't come but every few years and even with designated dark areas you

have to take a chance and be there on those special nights and if your lucky that's once or twice in the fall.

 

Regardless, between Sept & Oct of 22 we went out 3 times, third time to the good site,

But it was our first trip in sept second week that just knocked it out of the park.

Stuff that I've never seen under such clear and Stable skies,

and some stuff that was?  un-explainable??? ??

But you pay your money and you take your chances

 

 

 

So for myself  I'm really lucky to get "out" 3 or 4 scope times in the fall as that's after we get past all night twilight and smoke and  up to Dec/January when the real cold weather and reflecting snow hits.

-So we'll take every percentage point we can get when we get it and out.

Throughout of the rest of the year it's usually just naked eye viewing (like tonite) .

 

-----------------

 

 

 

There used to be a story floating around the net about the night of 6000x (or something to that effect)

In which the guys at a star party were stacking 2 or 3 barlows with their best eye pieces.

Those are exceptional nights and that's when you need that last little push up the hill.

Astronomy can be akin to drag racing in so much as every-bodies looking for that last 10th of a second.

 

 

 

 

-Tonight I'm probably gonna cycle the 10 miles out of town and should arrive near the old wooden trestle at

about 2 or 3 in the morning to watch the sun when it come up (around 3:30? -online sunset times/map not working).

I'll Work and do general shop choirs til it's time to head out as that's kind of the 'off season' norm.

 

Still hoping to see Noctilucent clouds as we are approaching the peak viewing window and tonight is said to be clear and warmish at 50F and at least for tonight we have little to no smoke as the recent rains have cleaned out the atmosphere.

 

So I will take you up on the offer of 'Clear Skies Tonite' and offer a cheers back to you,

 

moe

 

.

Edited by moefuzz, 17 June 2025 - 06:33 AM.

[Don W]

You guys are so serious! I started this thread with tongue in cheek. 

[George N]

The Bortle rating of a location is not determined by a color coded map. It’s determined by what you SEE, according to John Bortle himself:
https://skyandtelesc...arkSkyScale.pdf

......
It’s not a perfect scale, but it does have lots of good points.

Let’s respect John’s original intent.

I'm thinking you are 'tilting at windmills' - if you think any but a tiny fraction of long-time amateur astronomers will ever think of a "Bortle rating" in the sense that John intended. The vast majority know nothing of that article, or John's reason for the 'scale'. Whenever I read a post or hear a claim that "it is Bortle 4 at my observing site" I just assume the person is referring to a rating they found on an on-line light pollution map site. There is just not enough interest in making it anything else. Now add in general public, general science writers doing Light Pollution blog posts, etc - I see the original 'Bortle Scale' as a historical footnote - with the current and future meaning relegated to a general assessment of 'light polluted', or 'dark, but still compromised', or "so dark, I can only dream of being there once in my life."

 

I can still remember that Feb 2001 S&T arriving in my mailbox - reading the article and -- being both *depressed*  - and convinced that the "Bortle Scale" would never be of much value - especially in the 'fight' to control Light Pollution. The level of effort and experience needed to make a valid assessment is just too much for most people.  Plus, what's the point? Between then and now Google Gemini AI says the World population has increased 31.6% and the USA pop has increased 22.2%. We all know light pollution is today far worse than in 2001 - bad as it was then - and things like gas frack'ing have pushed major sky brightness out into otherwise low population areas.

 

I still think it is of value to make your own determination of darkness and other conditions at your observing sites - be they be outside your front door - or at some remote location that you can only reasonably expect to be at a few times in your life. A personal assessment/reading will be instructive to those who are still searching for a good observing site, considering that one-time retirement relocation, or want to contribute to fighting LP. I see the SQM or similar device as better for this than trying to make an 'eyeballs' assessment.

[George N]

You guys are so serious! I started this thread with tongue in cheek. 

What's the difference in Bortle Scale -- inside cheek - or outside? 

 

Oh ya..... is that with, or without -- lightning boltz......

Edited by George N, 17 June 2025 - 12:27 PM.