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No moon, the sun is down, no clouds, but the sky is still quite bright?

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#1 krokodilce

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Posted 20 September 2020 - 04:59 AM

Time for another beginner's question laugh.gif

 

Yesterday I've got out with my dob to a Bortle 3 spot (almost Bortle 2). The sky was fully clear, the moon was down as well and at 3% Waxing Crescent, I've been at the spot from 8 pm to 2 am, but the sky was so bright for some reason. It seemed like the full moon will popup on every cardinal direction. It was bright on the edges like 50% 50%, and at the top was like 25% blue and 75% dark.

 

Why is that, what is the fourth ingredient I need to consider? I was observing on the same spot during July, and there were some moments the sky was amazingly dark (I remember how impressed I was when the first time I saw M22 in a dark sky).

 

Clear and dark skies

 

EDIT: Location is Europe, Serbia, Latitude at 45° N


Edited by krokodilce, 20 September 2020 - 05:09 AM.


#2 james7ca

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Posted 20 September 2020 - 05:06 AM

You don't indicate your location, but if you are in the western U.S. then you may be seeing the effects of the wild fires that are burning out west. I live near San Diego and for the last week to ten days the skies have been cloudless but you really can't see any stars at night because of the smoke.



#3 Hesiod

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Posted 20 September 2020 - 05:08 AM

That does not sound a Bortle 3 site at all...the light domes seems that of a Bortle 5 at best.

#4 krokodilce

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Posted 20 September 2020 - 05:10 AM

You don't indicate your location, but if you are in the western U.S. then you may be seeing the effects of the wild fires that are burning out west. I live near San Diego and for the last week to ten days the skies have been cloudless but you really can't see any stars at night because of the smoke.

True, just added the location, it's Europe at 45° N latitude



#5 krokodilce

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Posted 20 September 2020 - 05:14 AM

That does not sound a Bortle 3 site at all...the light domes seems that of a Bortle 5 at best.

I was observing literally at the same spot multiple times and it was not nearly as bright as yesterday.

The data that says it is Bortle 3 I've got from https://www.lightpollutionmap.info/ map



#6 Hesiod

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Posted 20 September 2020 - 05:52 AM

Well, I am not so Scolastic to trust a map more than my own eyes 😁.

If see light domes as large as what you described, that it is not Bortle 3. Not by far.
A Bortle 3 site is almost "frightfully" dark.

By the way, I have just verified those map and does not seem very reliable.
I am now in the Italian Alps, at a Bortle 3 according the map.
The truth is that the site is Bortle 4 (but around Christmas and mid-August there is a noticeable increase of LP, bringing it almost to class 5).
My home town is rated as Bortle 5, but it is between 7 and 8!

#7 cookjaiii

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Posted 20 September 2020 - 07:45 AM

Apparent light pollution varies depending on what's suspended in the atmosphere.  Humidity, smoke, and dust all contribute by scattering and reflecting terrestrial light sources back down to earth.  

 

My location on the east coast of the US is Bortle 6 in Winter and Bortle 7 in humid Summer.  Last week, smoke from wildfires in the western US made my location, 2000 miles away, Bortle 8.

 

I don't know about your specific location, but sandstorms from Northern Africa blow huge amounts of dust into the air that drifts far distances.  In my experience, it affects the apparent light pollution all the way to the middle of Italy.  Could sandstorms in North Africa be the cause of your variable light pollution?  How about smoke?



#8 RobertMaples

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Posted 20 September 2020 - 08:04 AM

Even in Serbia, the problem may be the smoke from the wildfires in the western U.S.: https://www.space.co...ope-canada.html

 

Well, I am not so Scolastic to trust a map more than my own eyes .

If see light domes as large as what you described, that it is not Bortle 3. Not by far.
A Bortle 3 site is almost "frightfully" dark...

His point is it is normally a Bortle 3 area, though clearly not on the night in question.



#9 krokodilce

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Posted 20 September 2020 - 08:21 AM

Apparent light pollution varies depending on what's suspended in the atmosphere.  Humidity, smoke, and dust all contribute by scattering and reflecting terrestrial light sources back down to earth.  

 

My location on the east coast of the US is Bortle 6 in Winter and Bortle 7 in humid Summer.  Last week, smoke from wildfires in the western US made my location, 2000 miles away, Bortle 8.

 

I don't know about your specific location, but sandstorms from Northern Africa blow huge amounts of dust into the air that drifts far distances.  In my experience, it affects the apparent light pollution all the way to the middle of Italy.  Could sandstorms in North Africa be the cause of your variable light pollution?  How about smoke?

 

Even in Serbia, the problem may be the smoke from the wildfires in the western U.S.: https://www.space.co...ope-canada.html

 

His point is it is normally a Bortle 3 area, though clearly not on the night in question.

 

Wow, I didn't know that smoke in the western U.S. could impact that far. I didn't consider a possibility of that smoke or the dust from North Africa. I know that it couldn't be due to "casual" light pollution as this place is pretty far from any city or larger village, and my past observations from there were under a very dark sky, which is the reason I favoured this place.

 

Are there any tools that you can use to estimate factors such as smoke in the air or dust?


Edited by krokodilce, 20 September 2020 - 08:22 AM.


#10 BlueTrane2028

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Posted 20 September 2020 - 08:36 AM

Last night I was in Ottsville, a small town about an hour and change NW of Philadelphia. It’s between Philly and Allentown’s lights, not super dark but better than what is local to me.

Best DSO night of my life. Saw all of the Messier objects that weren’t right on the horizon, and that was with my 8”. Also best view ever of Andromeda.

Now I really know I have to get to Cherry Springs...

#11 Hesiod

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Posted 20 September 2020 - 10:30 AM

Even in Serbia, the problem may be the smoke from the wildfires in the western U.S.: https://www.space.co...ope-canada.html

His point is it is normally a Bortle 3 area, though clearly not on the night in question.


The attribution to class 3 is because of a website which us not very reliable, at least for Northern Italy.
He describes light domes, which are typical of ground-based light pollution, and failed to mention haze, so we have to assume that trabsparency was on average for the site.
I am around 45°N 10E and last Friday was out: the transparency was good as usual, bor thete was a "burning sunset", so the US wildfires are at least quite unlikely as culprits.
On the other hand man-mad LP is not always the same, depending on the sources' behavior: as said earlier, to make an example, around Christmas the LP in Val di Sole grows stronger due to greater amount of people living nearby and the habit of keeping light turned on

#12 John Fitzgerald

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Posted 20 September 2020 - 10:48 AM

When there is smoke, smog, etc., light pollution becomes worse and more widespread.  The smoke on the past several nights has turned my home site from Bortle 4.5 to a 9 or 10.


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#13 Tony Flanders

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Posted 20 September 2020 - 11:47 AM

I was observing literally at the same spot multiple times and it was not nearly as bright as yesterday.

The data that says it is Bortle 3 I've got from https://www.lightpollutionmap.info/ map

In my experience, that map almost always rates sites considerably darker than they actually are.

 

Even so, if your site is anywhere near Bortle 3 or 4, you must be a reasonable distance from the nearest city. However, high clouds -- or smoke -- can spread light pollution over a startlingly large area. On a truly clear night, the lights of a city 250 km distant -- even a truly huge one -- are very nearly invisible, being well over the bulge of Earth's sphere. However, cirrus clouds, smoke, volcanic ash, and so on can easily hang more than 5 km above Earth's surface. At that altitude, they are directly visible from a spot on the ground 250 km distant. And if they are directly over a major city, they will be brilliantly lit up.


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#14 Paul Sweeney

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Posted 21 September 2020 - 06:19 AM

I am having the same up here in Germany. Daytime skies are clear, nighttime skies are not very transparent and somewhat bright. This is caused by humidity or pollution. City lights, even those far away, shine up and illuminate the tiny particles floating high in the sky. Think of a planetary nebula. The density of the gas cloud is very low, but the central star lights it up enough to make it visible to us. After a good rain you should see a big improvement

#15 rhetfield

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Posted 21 September 2020 - 08:11 AM

Other possibilities could be zodiacal light and airglow.  These are things that one would see if the site is truly dark.

 

Otherwise, if the area is only bortle 3, then there is something in the area putting up light and any dust or humidity will enhance it.



#16 Ambush

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Posted 21 September 2020 - 09:33 AM

I live in one of the big rectangular states in western USA  and the smoke is most definitely putting a damper on observing.

As a newbie, I'm really enjoying this new hobby, but current conditions are making it difficult to indulge.

But considering what those poor people in those fire areas are having to contend with, I'm not going to complain much.



#17 krokodilce

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Posted 21 September 2020 - 11:50 AM

In my experience, that map almost always rates sites considerably darker than they actually are.

 

Even so, if your site is anywhere near Bortle 3 or 4, you must be a reasonable distance from the nearest city. However, high clouds -- or smoke -- can spread light pollution over a startlingly large area. On a truly clear night, the lights of a city 250 km distant -- even a truly huge one -- are very nearly invisible, being well over the bulge of Earth's sphere. However, cirrus clouds, smoke, volcanic ash, and so on can easily hang more than 5 km above Earth's surface. At that altitude, they are directly visible from a spot on the ground 250 km distant. And if they are directly over a major city, they will be brilliantly lit up.

Everything is clarified now and I understand what else can impact. Are there any tools that could help me with the estimation of smoke, dust or similar factors?




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