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Difference between Bortle 2 and 1

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#26 George N

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Posted 29 April 2021 - 10:02 AM

Ok, is the consensus Bortle 2 is practically the same as Bortle 1, if you don't look at the horizon? .....

Well if you want to know what Mr Bortle his-self said - read down the page here: https://skyandtelesc...dark-sky-scale/

 

When it comes to "horizons" -- my personal experience at Cherry Springs is - on humid nights there are two very dim and low light domes from the two local towns - and from the center of the "field" there is a full-circle low horizon - with no noticeable light at least in the South at the tree line. The S&T page notes that at Bortle 1 - a 20-inch will reach 19th magnitude visually. A year ago a friend showed up with a list of "billion light year galaxies" ( along with his 22-inch Dob ). The brightest was listed as 18th magnitude. We were able to see 4 of them - but certainly not the ones listed as 19th magnitude or dimmer. However - over the past 12 years - I've never seen the S&T described "zodiacal light to a striking degree" - but maybe I just missed it? I would rate it as Bortle 2 on most nights.

 

"Horizons"??? At my camp on Indian Lake in NY's Adirondacks -- 'the maps' say Bortle 2 -- However - I'm surrounded by mile high mountains - the only low horizon is straight South down the 16 mile long lake - and it is starting to show a low light dome on hazy nights - thanks to commercial development in the Saratoga area I guess. I can see M-33 naked eye - but no gegenschein or 'natural sky glow' - still, folks from places like NYC and Albany are shocked into paralysis by the sight of the Milky Way! I would rate it as "Bortle 2".

 

While we are discussing "Bortle Scale" in another thread - I have always understood it as a way for an observer to describe what *they* experienced at a specific time - so others could understand their observational descriptions - and not so much as a general description of Light Pollution at a location.

 

Bottom line -- It seems to me that the 'difference' is -- the following is easier to see at Bortle 1 vs 2: "The zodiacal light, gegenschein, and zodiacal band....." and the natural sky glow that sometimes appears is easy to see at Bortle 1, but not 2 - (Edward Emerson Barnard wrote a paper about 1900 complaining about sky glow messing up his wide-field photographs). While I've seen the zodiacal light at dark locations in NY -- I've never seen the gegenschein or obvious "natural sky glow". That seems to be reserved today for sites in Western North America.


Edited by George N, 29 April 2021 - 10:17 AM.

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#27 viewer

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Posted 29 April 2021 - 01:39 PM

Thanks! Much to think about. Maybe a "good" Bortle 2 would be the thing to start hunting for on the light pollution maps, but by no means saying no to the possibly best Bortle 1 in the country, if it's practically doable. Greed is seldom good though.



#28 LDW47

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Posted 29 April 2021 - 07:10 PM

Ok, is the consensus Bortle 2 is practically the same as Bortle 1, if you don't look at the horizon? Could take a trip to the northernmost Lapland, after carefully checking the weather reports and of course the moon(less) situation in autumn. Then the northern lights could be a possible bonus, naturally "destroying" the starry sky. But if not hunting for the 1, being content with 2, there are many more options where to stay. Would you take 2?

You sure wouldn’t be disappointed with Bortle 2 ! 



#29 LDW47

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Posted 29 April 2021 - 07:12 PM

Well if you want to know what Mr Bortle his-self said - read down the page here: https://skyandtelesc...dark-sky-scale/

 

When it comes to "horizons" -- my personal experience at Cherry Springs is - on humid nights there are two very dim and low light domes from the two local towns - and from the center of the "field" there is a full-circle low horizon - with no noticeable light at least in the South at the tree line. The S&T page notes that at Bortle 1 - a 20-inch will reach 19th magnitude visually. A year ago a friend showed up with a list of "billion light year galaxies" ( along with his 22-inch Dob ). The brightest was listed as 18th magnitude. We were able to see 4 of them - but certainly not the ones listed as 19th magnitude or dimmer. However - over the past 12 years - I've never seen the S&T described "zodiacal light to a striking degree" - but maybe I just missed it? I would rate it as Bortle 2 on most nights.

 

"Horizons"??? At my camp on Indian Lake in NY's Adirondacks -- 'the maps' say Bortle 2 -- However - I'm surrounded by mile high mountains - the only low horizon is straight South down the 16 mile long lake - and it is starting to show a low light dome on hazy nights - thanks to commercial development in the Saratoga area I guess. I can see M-33 naked eye - but no gegenschein or 'natural sky glow' - still, folks from places like NYC and Albany are shocked into paralysis by the sight of the Milky Way! I would rate it as "Bortle 2".

 

While we are discussing "Bortle Scale" in another thread - I have always understood it as a way for an observer to describe what *they* experienced at a specific time - so others could understand their observational descriptions - and not so much as a general description of Light Pollution at a location.

 

Bottom line -- It seems to me that the 'difference' is -- the following is easier to see at Bortle 1 vs 2: "The zodiacal light, gegenschein, and zodiacal band....." and the natural sky glow that sometimes appears is easy to see at Bortle 1, but not 2 - (Edward Emerson Barnard wrote a paper about 1900 complaining about sky glow messing up his wide-field photographs). While I've seen the zodiacal light at dark locations in NY -- I've never seen the gegenschein or obvious "natural sky glow". That seems to be reserved today for sites in Western North America.

Or Northern Ontario !



#30 viewer

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Posted 30 April 2021 - 10:46 AM

You sure wouldn’t be disappointed with Bortle 2 ! 

Good to know, must put the project forward at least on a fantasy level!

 

Smack in the middle of the Lemmenjoki Kansallispuisto would provide a fair, maybe even a good Bortle 1: https://www.lightpol...FFFTFFFFFFFFFF 

About 75 kilometers from a small town, where to fly and rent a car. Driving 150 kilometers in a night is definitely doable. Jumping out of the car now and then for the Bortle countdown...

 

Edit: maybe I will have to be content with a "bad" Bortle 1. Appears to be no roads to the best place bangbang.gif


Edited by viewer, 30 April 2021 - 11:43 AM.


#31 MJB87

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Posted 04 May 2021 - 08:05 AM

Let's stay on topic please. Off-topic posts are removed and the posters are invited to start a new thread in the appropriate forum.



#32 RLK1

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Posted 04 May 2021 - 09:54 AM

I'm skeptical that you can have a Bortle 1 sky over an appreciable land mass these days and I suspect if one is even possible, given the ever increasing contributions of mankind to artificial sky glow, it's probably over open ocean somewhere in the pacific or over the north atlantic. So, the best you can hope for probably is a bortle 2 sky. I have further skepticism regarding the criteria within the bortle classification itself. A bortle 1 sky purportedly includes visual detection of magnitude 8 stars. Here's my problem with that: scientific sources that I 've have read, including those from Harvard and NASA, report a limiting visual magnitude with the unaided eye to be seven with a literature range of 6-8,  with an 8 being reported in amateur sources such as those found in popular magazines like Sky & Telescope. Whom to believe?  So, while there are stated reasons for a difference between a bortle 1 and 2 sky, given the ever increasing sky brightness for several reasons, I think the best one can hope for is what is more realistically referred to as a bortle 2 sky. 



#33 LDW47

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Posted 04 May 2021 - 01:10 PM

I'm skeptical that you can have a Bortle 1 sky over an appreciable land mass these days and I suspect if one is even possible, given the ever increasing contributions of mankind to artificial sky glow, it's probably over open ocean somewhere in the pacific or over the north atlantic. So, the best you can hope for probably is a bortle 2 sky. I have further skepticism regarding the criteria within the bortle classification itself. A bortle 1 sky purportedly includes visual detection of magnitude 8 stars. Here's my problem with that: scientific sources that I 've have read, including those from Harvard and NASA, report a limiting visual magnitude with the unaided eye to be seven with a literature range of 6-8,  with an 8 being reported in amateur sources such as those found in popular magazines like Sky & Telescope. Whom to believe?  So, while there are stated reasons for a difference between a bortle 1 and 2 sky, given the ever increasing sky brightness for several reasons, I think the best one can hope for is what is more realistically referred to as a bortle 2 sky. 

Come up to northern Canada, the places I travel, the places I view, you will get all the Bortle 1 skies you will ever need and then some ! Not all places in the world are painted with your brush believe me ! And that land mass goes on a long ways in any direction !



#34 Augustus

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Posted 04 May 2021 - 09:34 PM

Well if you want to know what Mr Bortle his-self said - read down the page here: https://skyandtelesc...dark-sky-scale/

 

When it comes to "horizons" -- my personal experience at Cherry Springs is - on humid nights there are two very dim and low light domes from the two local towns - and from the center of the "field" there is a full-circle low horizon - with no noticeable light at least in the South at the tree line. The S&T page notes that at Bortle 1 - a 20-inch will reach 19th magnitude visually. A year ago a friend showed up with a list of "billion light year galaxies" ( along with his 22-inch Dob ). The brightest was listed as 18th magnitude. We were able to see 4 of them - but certainly not the ones listed as 19th magnitude or dimmer. However - over the past 12 years - I've never seen the S&T described "zodiacal light to a striking degree" - but maybe I just missed it? I would rate it as Bortle 2 on most nights.

 

"Horizons"??? At my camp on Indian Lake in NY's Adirondacks -- 'the maps' say Bortle 2 -- However - I'm surrounded by mile high mountains - the only low horizon is straight South down the 16 mile long lake - and it is starting to show a low light dome on hazy nights - thanks to commercial development in the Saratoga area I guess. I can see M-33 naked eye - but no gegenschein or 'natural sky glow' - still, folks from places like NYC and Albany are shocked into paralysis by the sight of the Milky Way! I would rate it as "Bortle 2".

 

While we are discussing "Bortle Scale" in another thread - I have always understood it as a way for an observer to describe what *they* experienced at a specific time - so others could understand their observational descriptions - and not so much as a general description of Light Pollution at a location.

 

Bottom line -- It seems to me that the 'difference' is -- the following is easier to see at Bortle 1 vs 2: "The zodiacal light, gegenschein, and zodiacal band....." and the natural sky glow that sometimes appears is easy to see at Bortle 1, but not 2 - (Edward Emerson Barnard wrote a paper about 1900 complaining about sky glow messing up his wide-field photographs). While I've seen the zodiacal light at dark locations in NY -- I've never seen the gegenschein or obvious "natural sky glow". That seems to be reserved today for sites in Western North America.

I've never heard of anyone hitting magnitude 19 with a 20", let alone on a diffuse object.

 

I'm skeptical that you can have a Bortle 1 sky over an appreciable land mass these days and I suspect if one is even possible, given the ever increasing contributions of mankind to artificial sky glow, it's probably over open ocean somewhere in the pacific or over the north atlantic. So, the best you can hope for probably is a bortle 2 sky. I have further skepticism regarding the criteria within the bortle classification itself. A bortle 1 sky purportedly includes visual detection of magnitude 8 stars. Here's my problem with that: scientific sources that I 've have read, including those from Harvard and NASA, report a limiting visual magnitude with the unaided eye to be seven with a literature range of 6-8,  with an 8 being reported in amateur sources such as those found in popular magazines like Sky & Telescope. Whom to believe?  So, while there are stated reasons for a difference between a bortle 1 and 2 sky, given the ever increasing sky brightness for several reasons, I think the best one can hope for is what is more realistically referred to as a bortle 2 sky. 

Well, that's some doom and gloom. I have seen magnitude 7.2 stars naked eye from what would be called a "B3" so I don't see why 8 isn't possible. 

 

IMO:

The Bortle scale is arbitrary nonsense, and should be retired in favor of SQM when it comes to rating a site in general.



#35 kel123

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Posted 04 May 2021 - 10:13 PM

Frankly, I think if you don't try it at least once, you will never stop imagining it.
So, I guess you should go for it, at least once to satisfy your curiosity. You might even discover other advantages to the location or otherwise.
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#36 Tony Flanders

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Posted 05 May 2021 - 04:35 AM

I'm skeptical that you can have a Bortle 1 sky over an appreciable land mass these days and I suspect if one is even possible, given the ever increasing contributions of mankind to artificial sky glow, it's probably over open ocean somewhere in the pacific or over the north atlantic.


Contrary to the implications of Bortle's article, artificial light is not the only impediment -- or in many cases the biggest impediment -- to deep-sky observing. Both in skies usually classed as Bortle 1 and in skies usually classed as Bortle 2, artificial light is a negligible issue except possibly if you're observing low in the sky in the direction of the major light source. At good sites in the American West -- or anywhere else -- transparency is a much bigger issue than artificial light pollution. The difference between seeing the things that John Bortle describes as defining his Class 1 and not seeing them is almost entirely a matter of transparency, once you get reasonably far from all major light sources. Which is exceptionally easy to do throughout the American West -- and much easier in places like Australia.

Pretty much everyone I know who has observed from the visitor's center at Mauna Kea -- or better, from the top (a select few) -- has been wowed by the experience. Yet the top of Mauna Kea is just 26 miles (40 km) from the center of Hilo, the second-biggest city in Hawai'i. From the top of Mauna Kea all the lights of Hilo and Waimea are directly visible. Likewise, from the top of Kitt Peak (no slouch as an observing site) all the lights of Tucson are spread out beneath you.


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#37 kel123

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Posted 05 May 2021 - 06:00 AM

I don't think John Bortle would discount other impediments but he was looking at light pollution in isolation of the other impediments. For example, you will see nothing if it is cloudy as an always cloudy Bottle 1 is useless.

Also, it is significantly different when light sources are below you than when they are above you.

I love observing at high altitudes. When you are at a high altitude, you tend to see things you shouldn't see, meaning that you may see objects that are yet to rise according to planateriums.

#38 RLK1

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Posted 05 May 2021 - 12:02 PM

Contrary to the implications of Bortle's article, artificial light is not the only impediment -- or in many cases the biggest impediment -- to deep-sky observing. Both in skies usually classed as Bortle 1 and in skies usually classed as Bortle 2, artificial light is a negligible issue except possibly if you're observing low in the sky in the direction of the major light source. At good sites in the American West -- or anywhere else -- transparency is a much bigger issue than artificial light pollution. The difference between seeing the things that John Bortle describes as defining his Class 1 and not seeing them is almost entirely a matter of transparency, once you get reasonably far from all major light sources. Which is exceptionally easy to do throughout the American West -- and much easier in places like Australia.

Pretty much everyone I know who has observed from the visitor's center at Mauna Kea -- or better, from the top (a select few) -- has been wowed by the experience. Yet the top of Mauna Kea is just 26 miles (40 km) from the center of Hilo, the second-biggest city in Hawai'i. From the top of Mauna Kea all the lights of Hilo and Waimea are directly visible. Likewise, from the top of Kitt Peak (no slouch as an observing site) all the lights of Tucson are spread out beneath you.

I'm not stating artificial skyglow is the only impediment to what is described as a bortle 1 sky, Certainly light pollution from city lights, as you've noted above, continue to be an ever growing problem. And, if one chooses to adhere to the criteria noted in a bortle 1 sky, if you're seeing the glow from city lights, you're not in a bortle 1 sky, no matter how wowed you might be...



#39 MarMax

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Posted 05 May 2021 - 01:35 PM

This continues to be a great thread. As I do not have the experience to estimate seeing and transparency or a Bortle classification, I've purchased an SQM. The darkest site I've visited (twice now) is Darwin, CA. The visits were in October 2020 and April 2021 so you can't really compare them since the sky was different.

 

Both visits had different conditions each night of the three nights we were there per visit. I'll only discuss what I saw when it was clear (no clouds) since you can't really evaluate things with any type of high clouds or haze. There was some smoke from the wildfires in October but at the best times I felt the Milky Way was more obvious in general in October than in April.

 

Each trip had a best night where my wife and I agreed things looked better. I did not have the SQM meter in October but I think the best night overall was in October. In April the SQM measurements were 21.96 to 22.00 and even with these readings I felt that the Milky Way was not as obvious as October. There was only a 3-4 hour period during April that had very good conditions.

 

So in light of the discussion so far, both trips would probably be Bortle 2, even though the SQM was 22.00. I actually did not think that the meter would register a 22.00. So I can see as Tony suggests how transparency is so important.



#40 LDW47

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Posted 05 May 2021 - 03:31 PM

This continues to be a great thread. As I do not have the experience to estimate seeing and transparency or a Bortle classification, I've purchased an SQM. The darkest site I've visited (twice now) is Darwin, CA. The visits were in October 2020 and April 2021 so you can't really compare them since the sky was different.

 

Both visits had different conditions each night of the three nights we were there per visit. I'll only discuss what I saw when it was clear (no clouds) since you can't really evaluate things with any type of high clouds or haze. There was some smoke from the wildfires in October but at the best times I felt the Milky Way was more obvious in general in October than in April.

 

Each trip had a best night where my wife and I agreed things looked better. I did not have the SQM meter in October but I think the best night overall was in October. In April the SQM measurements were 21.96 to 22.00 and even with these readings I felt that the Milky Way was not as obvious as October. There was only a 3-4 hour period during April that had very good conditions.

 

So in light of the discussion so far, both trips would probably be Bortle 2, even though the SQM was 22.00. I actually did not think that the meter would register a 22.00. So I can see as Tony suggests how transparency is so important.

I hope it was the SQM-L model ?



#41 MarMax

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Posted 05 May 2021 - 03:46 PM

I hope it was the SQM-L model ?

Yes, SQM-L.


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#42 viewer

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Posted 05 May 2021 - 03:58 PM

Interesting enough the Light pollution map lists only SQM 22.00 as a clear Bortle 1, while 21.99 can be also Bortle 2. Looks the "Ratio" function is good, differentiates between good and not so good SQM 22.00 / Bortle 1 areas. Want to get really dark and low Ratio? Take to the oceans!



#43 LDW47

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Posted 05 May 2021 - 06:06 PM

Interesting enough the Light pollution map lists only SQM 22.00 as a clear Bortle 1, while 21.99 can be also Bortle 2. Looks the "Ratio" function is good, differentiates between good and not so good SQM 22.00 / Bortle 1 areas. Want to get really dark and low Ratio? Take to the oceans!

Or northern Ontario !



#44 MikeTahtib

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Posted 05 May 2021 - 06:48 PM

Yes, SQM-L.

What's the difference between the M and L models?
 



#45 MarMax

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Posted 05 May 2021 - 07:05 PM

What's the difference between the M and L models?
 

The SQM-L has a narrow field of view.



#46 Tony Flanders

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Posted 06 May 2021 - 04:02 AM

Here's another way of saying what I said earlier, about skyglow and transparency.

 

The difference between a Bortle 1 sky and a Bortle 2 sky is significant by definition. If you want to know what the difference is, read Bortle's article.

 

However, the difference between a site shown on a light-pollution map as Bortle 1 and a site shown on a light-pollution map as Bortle 2 is not necessarily significant. And conditions at any given site far from artificial lights are likely to be Bortle 1 on some nights and Bortle 2 on others.


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#47 viewer

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Posted 06 May 2021 - 09:01 AM

True. But I'd bet though a Bortle 1 area on average is better than a Bortle 2 area, especially if it's nearby. Another way to put it: being a Bortle 1 spot on the map doesn't hurt wink.gif. Then it's up to luck!


Edited by viewer, 06 May 2021 - 09:02 AM.


#48 viewer

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Posted 06 May 2021 - 09:16 AM

Or northern Ontario !

You are indeed right. Ratio: 0. Light pollution is almost an unknown entity there.


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