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.