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Bortle 5 to a Bortle 4...big diff?

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#1 bujin9

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Posted 24 May 2024 - 06:42 AM

Hi...quick question regarding Bortle scale and viewing...
I live in a B5 area...about 45 min away is B4, is a B4 from a B5 a significant change?
I ask cause it's pretty easy viewing from my driveway ( as I just roll out the dob from my garage and roll it back in)...but breaking down, loading in my car, then setting back up (and then breaking down again at the end of the night) is a lot more involved obviously. We have no B3 in near me as far as I know...maybe a few hours away.
thanks,
Joe



#2 Nankins

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Posted 24 May 2024 - 06:57 AM

Not too much until you get to the very low B4. My area is technically B4. But it's quickly becoming B5 and there's even a difference between the end of our neighborhood and where our house is.

#3 bujin9

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Posted 24 May 2024 - 07:17 AM

Ok...thanks...I'm probably a 5 maybe getting near 4.5 so that's what I figured. My trees are a bit of an issue and sound's like that'd be the only reason to venture to a 'cleaner' site.



#4 Keith Rivich

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Posted 24 May 2024 - 08:10 AM

Hey bujin9,

 

It would really help if we knew where you are observing from. Doesn't have to be exact but a general idea. If you read through past threads on this topic you will discover Bortle means little to nothing without context. 

 

Another plus to knowing location is others here may live near the same area and could guide you on observing locations. 


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#5 bujin9

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Posted 24 May 2024 - 08:20 AM

Hi Keith, I'm in Southern Connecticut near Monroe. If I look at the Connecticut dark sky sites (per this website     https://www.go-astro...te.php?State=CT), it show's only B4. That being said, certainly the northern parts of the state probably have better seeing than southern parts (from a transparency standpoint). But I'd hope they were significantly better than where I am to make the journey.

Another map used is:

https://www.lightpol...WNpdHkiOjg1fQ==


Edited by bujin9, 24 May 2024 - 08:23 AM.

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#6 Sebastian_Sajaroff

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Posted 24 May 2024 - 10:11 AM

There is no such thing as Bortle "areas".
Bortle scale describes local conditions at a specific moment (now) for a specific observer (you).

Some spot in the middle of the Atacama desert on a clear New Moon night will usually be B1-B2.
Same place during a dusty windy night may be B3-B4
Once again, same spot on Full Moon turns into B7-B8, same as living 20 miles away from Manhattan.

Let’s suppose I go to Atacama with my 85 years old mother during one of those marvellous New Moon nights.
Sky may be B1 to me but B4-B5 to her, her eyes are not on the same condition as mine.
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#7 sevenofnine

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Posted 24 May 2024 - 01:21 PM

At one time my location ranged from B-3 toward the vineyards south of town to B-5 to the north over the city. There's a big difference between 3&5 but B-4 would be worth investigating IMO. I would take a pair of astro binoculars and compare the views. If other conditions are better then it could be worth the effort and drive borg.gif


Edited by sevenofnine, 24 May 2024 - 07:54 PM.


#8 havasman

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Posted 24 May 2024 - 02:55 PM

If you're getting your darkness ratings from a map they're probably outdated and inaccurate. Even if they're not you really aren't going to get your best answer except by going to your alternate site and trying it out. Even then, conditions change between nights and over time generally. It's a ~frustrating constant of the hobby that we all deal with.


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#9 erictheastrojunkie

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Posted 24 May 2024 - 03:56 PM

There is no such thing as Bortle "areas".
Bortle scale describes local conditions at a specific moment (now) for a specific observer (you).

Some spot in the middle of the Atacama desert on a clear New Moon night will usually be B1-B2.
Same place during a dusty windy night may be B3-B4
Once again, same spot on Full Moon turns into B7-B8, same as living 20 miles away from Manhattan.

Let’s suppose I go to Atacama with my 85 years old mother during one of those marvellous New Moon nights.
Sky may be B1 to me but B4-B5 to her, her eyes are not on the same condition as mine.

That's not how it works, the bortle scale is based on a sky magnitude quality meter, something isn't a bortle X to one person and a bortle Y to another, it is a bortle value based on an independent measurement made by a calibrated instrument. We also don't refer to a location's bortle scale value based on it's brightness under various moonlit conditions, it goes without saying that the sky brightness magnitude is dramatically impacted by the moon and that's not the intent of assigning a bortle value to a location. We refer to a location's general bortle scale value as a way of generalizing the quality of that location's sky under ideal circumstances, ie no moon, clear skies, no snow, etc, it may change slightly from night to night under non-moonlit conditions, but that's why websites like the lightpollutionmap one gives average readings over months and years. 


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#10 Jawaid I. Abbasi

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Posted 24 May 2024 - 07:08 PM

The best way is the NELM



#11 Oldfracguy

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Posted 24 May 2024 - 09:02 PM

Even though the atmospheric seeing changes from night to night, and even in a matter of hours on a single night, the amount of ambient light pollution from surrounding areas does not.  Using these generic light pollution maps still has value.  All that being said, I suspect you will see only a small incremental improvement going from your Bortle 5 area to a Bortle 4 region.  In fact, I predict that if you tried it a couple times you would conclude that it's not worth the trouble.

 

On the other hand, consider yourself fortunate to actually live in a Bortle 5 area.  I relish the opportunity to pack up the car and drive about an hour or so once every few months from my Bortle 7 home to a Bortle 4 region for an overnight observing session.  The difference between Bortle 7 and Bortle 4 is startling.  Things I have to use a 9x50 finder scope to locate at home I can see with the naked eye under dark skies.


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#12 CrazyPanda

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Posted 24 May 2024 - 11:50 PM



That's not how it works, the bortle scale is based on a sky magnitude quality meter, something isn't a bortle X to one person and a bortle Y to another, it is a bortle value based on an independent measurement made by a calibrated instrument. We also don't refer to a location's bortle scale value based on it's brightness under various moonlit conditions, it goes without saying that the sky brightness magnitude is dramatically impacted by the moon and that's not the intent of assigning a bortle value to a location. We refer to a location's general bortle scale value as a way of generalizing the quality of that location's sky under ideal circumstances, ie no moon, clear skies, no snow, etc, it may change slightly from night to night under non-moonlit conditions, but that's why websites like the lightpollutionmap one gives average readings over months and years. 

Bortle scale is a qualitative (not quantitative) assessment of a sky's typical conditions. SQM reading may be a factor, but isn't necessarily a required one.

 

The whole purpose of the Bortle scale is to give a description of what the conditions might be like at a given site. In my area, snow covered ground gives very different conditions than non snow covered ground. It's not accurate to call my site a class 4 site when there's snow on the ground and the sky behaves more like a class 5 or 6 sky for 3 months out of the year.

 

If I'm trying to describe the conditions to someone else, it's perfectly valid for me to give an estimated Bortle value appropriate for the night's conditions.

 

It's also valid to take the Moon into account. If someone wants to visit a class 1 site because they heard class 1 skies are the darkest, but they plan on visiting during a full Moon, saying "The sky will be more like a typical class 7 or 8 sky under such conditions" is a valid and useful comparison.


Edited by CrazyPanda, 24 May 2024 - 11:52 PM.

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#13 Sebastian_Sajaroff

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Posted 25 May 2024 - 06:03 AM

That's not how it works, the bortle scale is based on a sky magnitude quality meter, something isn't a bortle X to one person and a bortle Y to another, it is a bortle value based on an independent measurement made by a calibrated instrument. We also don't refer to a location's bortle scale value based on it's brightness under various moonlit conditions, it goes without saying that the sky brightness magnitude is dramatically impacted by the moon and that's not the intent of assigning a bortle value to a location. We refer to a location's general bortle scale value as a way of generalizing the quality of that location's sky under ideal circumstances, ie no moon, clear skies, no snow, etc, it may change slightly from night to night under non-moonlit conditions, but that's why websites like the lightpollutionmap one gives average readings over months and years.


No, doesn’t work like that.
Bortle scale is subjective, he didn’t take any measures, just described what he saw from different skies.
SQM measures sky darkness but says nothing about its transparency; which is fundamental to see objects mentioned by Bortle like gegenschein, zodiacal light, M33, etc.
Maps and apps are rarely updated, 5 or 10 years is a lot of time for light pollution. My own backyard downgraded from B6 to B9 in a decade.

#14 Keith Rivich

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Posted 25 May 2024 - 07:49 AM

Get the Dark Sky Meter for your phone if you don't want to spend $160 for a SQML. Not as accurate but it works pretty well. 


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#15 erictheastrojunkie

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Posted 25 May 2024 - 01:51 PM

Bortle scale is a qualitative (not quantitative) assessment of a sky's typical conditions. SQM reading may be a factor, but isn't necessarily a required one.

The whole purpose of the Bortle scale is to give a description of what the conditions might be like at a given site. In my area, snow covered ground gives very different conditions than non snow covered ground. It's not accurate to call my site a class 4 site when there's snow on the ground and the sky behaves more like a class 5 or 6 sky for 3 months out of the year.

If I'm trying to describe the conditions to someone else, it's perfectly valid for me to give an estimated Bortle value appropriate for the night's conditions.

It's also valid to take the Moon into account. If someone wants to visit a class 1 site because they heard class 1 skies are the darkest, but they plan on visiting during a full Moon, saying "The sky will be more like a typical class 7 or 8 sky under such conditions" is a valid and useful comparison.

the bortle scale is not qualitative, it is quantitative, each level of the scale has a defined range of SQM:
https://en.m.wikiped...ki/Bortle_scale

The scale has some qualitative aspects, trying to describe how well some things in the sky can be seen under each level of the scale, but the underlying way we determine each level is by its SQM.

Again, any site on earth will become "bortle 8" under a full Moon, regardless of its typical bortle scale under dark conditions. That doesn't help us classify a specific area relative to its actual sky quality.

#16 Captain Quark

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Posted 25 May 2024 - 09:15 PM

I frequent two sites one of which is generally B5 and one B4. The B5 has a couple of light domes that are more obnoxious than the B4’s which restricts those parts of the sky.  I was able to observe Pluto at the B4 and not the B5. There are more naked eye Messiers at the B4. Uranus is naked eye at the B4. All DSOs look better at the B4. M31, M33, M81/82 all show more at the B4. Go try it!


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#17 CrazyPanda

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Posted 25 May 2024 - 10:45 PM

The scale has some qualitative aspects

 

Difference of opinion then. The Bortle scale is, and always has been, intended to be a means of describing visually what a site is like. Thus 90% of the facets that make up the scale are in fact qualitative in nature, and SQM - the only quantitative criterion - is just a small piece of the picture.

 

Otherwise, what's the point of anything else in the scale? If the SQM reading is all that matters, ditch the Bortle scale entirely and just refer to a site by its average SQM reading in a given season. SQM gives me a number. Bortle classification gives me a picture.

 

 

 

That doesn't help us classify a specific area relative to its actual sky quality.

 

No it doesn't, but that wasn't my point. My point was simple: depending on when you visit a dark sky site, the effective Bortle scale may not be what it typically is. I've seen plenty of posts in other communities of people asking how bad things will be with the Moon in the sky in a class 1 site, and saying "It will be the equivalent of being under class 6/7/8/9 skies" is a valid way to give them a frame of reference for what to expect.


Edited by CrazyPanda, 25 May 2024 - 10:46 PM.


#18 Bob4BVM

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Posted 26 May 2024 - 03:03 PM

Bortle-schmortle...I pay almost no attention to any of these 'scales'

 

All my searching is done by simply studying maps, google earth, and other geo resources.

Then i select areas as far as possible from habitation in any direction, with site altitude always a consideration.

 

The results have been greatly rewarding.

My description of my all-time favorite site is:

"9700FASL & 100 miles from the nearest streetlight"

 

Its a 6-hr drive for me but well worth it, i try to spend a couple weeks a year up there during new moon periods.  Surreal experience.

 

-B



#19 m1thumb

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Posted 28 May 2024 - 07:53 PM

I'm moving from a high B5 to a lower B4. The difference is significant to my eyes.

#20 tcifani

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Posted 28 May 2024 - 09:05 PM

Hi...quick question regarding Bortle scale and viewing...
I live in a B5 area...about 45 min away is B4, is a B4 from a B5 a significant change?
I ask cause it's pretty easy viewing from my driveway ( as I just roll out the dob from my garage and roll it back in)...but breaking down, loading in my car, then setting back up (and then breaking down again at the end of the night) is a lot more involved obviously. We have no B3 in near me as far as I know...maybe a few hours away.
thanks,
Joe

Give this map a look. I've read (here on CN) that this light pollution map is more updated than the others. No Bortle ratings are given, just sky brightness. To answer your original question, I do see a difference from B5 to B4. Although sky transparency may actually be more important at these suburban to rural places than a Bortle 4 or 5 designation. For me, B4 is a decent drive from the city but well worth it. More Milky Way to see. More faint fuzzies. Fewer and smaller light domes from cities. I agree with Bob4BVM's above idea: "I select areas as far as possible from habitation..."

 

https://djlorenz.git...erlay/dark.html



#21 skpark

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Posted 02 June 2024 - 07:21 PM

Im pretty close to Monroe. On moonless nights i get around 20.50 SQM. Maps show my area as B5 and i tend to agree but there’s plenty of micro light pollution “climates”. My property is surrounded by a nature preserve, which helps significantly. Personally i think a B5 to B4 is a noticeable jump.


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