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Why is my sky so bright?

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40 replies to this topic

#26 Starman1

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Posted 11 November 2018 - 02:19 PM

Many people report that November has been a particularly unclear month, whether it is due to smoke from fires or simply high altitude haze.


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#27 Kent10

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Posted 11 November 2018 - 02:55 PM

Many people report that November has been a particularly unclear month, whether it is due to smoke from fires or simply high altitude haze.

Good to know.  Thanks.  I'll keep checking and hope for improved darkness.  It would be interesting to drive out some way north of the city to see what readings I get there.



#28 Kent10

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Posted 11 November 2018 - 11:48 PM

Tonight a slightly darker sky at 20.90 but the worst seeing I have ever seen.  I did not stay out long to view.  I went out three separate times to check the seeing.  Terrible even at the lowest powers.  Perhaps there was wind in the upper atmosphere that was clearing out particles in the sky to make it darker.  I could still smell the local fireplaces though.  It was a windy day but there was no wind at my site this evening but I assume it was very windy in the upper atmosphere.



#29 rockethead26

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Posted 12 November 2018 - 09:47 AM

Tonight a slightly darker sky at 20.90 but the worst seeing I have ever seen.  I did not stay out long to view.  I went out three separate times to check the seeing.  Terrible even at the lowest powers.  Perhaps there was wind in the upper atmosphere that was clearing out particles in the sky to make it darker.  I could still smell the local fireplaces though.  It was a windy day but there was no wind at my site this evening but I assume it was very windy in the upper atmosphere.

I was going to give it a go last night, too. I checked Meteoblue for the seeing report and saw it was going to be bad, walked outside at 7 pm and could see transparency issues and could smell the neighborhood smoke. Add in that it was pretty darn cold already so I called it off. I'm working at Lowell tonight, and it's going to be cold! I'm curious as to the transparency on Mars Hill tonight as compared to our neighborhood over the last few nights.



#30 StarBurger

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Posted 13 November 2018 - 03:00 PM

I often wonder if loss of leaves affects very local light pollution in the winter months.

When the leaves fall from my surrounding trees I see more of the further distant street lamps that were masked before but at the same time the trees are not lit up so strongly with illuminated leaves.

It's a bit of give and take I suppose.



#31 Starman1

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Posted 13 November 2018 - 04:06 PM

No leaves and snow on the ground used to make the night a lot brighter where I grew up.

Add the fact the Full Moon is far north in the sky and night is a lot brighter in the winter.

Here in SoCal, I don't see a lot of difference--it's just bright all the time.lol.gif bawling.gif



#32 oldmanrick

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Posted 13 November 2018 - 09:07 PM

I live in a Bortle 2 zone and the Zodiacal Light has been VERY bright in the morning skies.

 

John Rogers

I too have occasionally noticed a portion of the sky being noticeably brighter due to the Zodiacal Light.

 

Seems like I notice it more in the summer, maybe because I'm out more and longer.

 

Also, lately I've been seeing what I think may be a faint whitish glow caused by Aurora Borealis activity.  I've seen this many times, usually toward the horizon, and in  the northern quadrants of the sky.  It usually varies somewhat by the hour and sometimes changes so rapidly that changes are detectable from one minute to the next.

 

I have definitely noticed the sky being brighter during the last few nights, but just attributed it to Aurora activity.


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#33 Jon Isaacs

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Posted 14 November 2018 - 06:21 AM

Many people report that November has been a particularly unclear month, whether it is due to smoke from fires or simply high altitude haze.

 

I have noticed that November has been much brighter the last two years since I have had a SQM-L.  Typically the skies in the high desert are 21.3 at higher elevations, sometimes 21.5 if the coast is clouded up.  But this November and last November it has been 21.0-21.05 at 60 degrees plus.  I don't think it's light pollution because it did become darker again.  

 

Those three nights you were at Night Fall, I was about 50 miles south and experienced those same high clouds. But then it cleared up nicely and the skies were still bright.

 

Jon



#34 Jeff B1

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Posted 14 November 2018 - 08:25 AM

Maybe it's the sunlight illuminating planetary debris from the planet Vulcan lol.gif  They call it Zodiacal-Spock Light


Edited by Jeff B1, 14 November 2018 - 08:27 AM.


#35 vsteblina

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Posted 14 November 2018 - 02:31 PM

I live in the dark sky city of Flagstaff, AZ, the 1st International Dark Sky City.  Lately, the skies seem brighter than usual.

 

I have a Sky Quality Meter and have been measuring the darkness over the last few days and it has been around 20.7.  There is no moon.  Just a few months ago, I measured the sky at 21.15-21.2.  That is the darkest I have measured.  It isn't always that dark but the sky appears brighter now so that is why I have been measuring it the last few days.

 

Why do you think it is noticeably brighter?  It is not very humid so there isn't a lot of moisture in the air but maybe it is more humid than my darker measurements.  Would that make such a large difference?  Could more homes have their lights on?  Dirt in the air?

 

I am concerned and want it dark again.  We have some new street lights installed across  the city, but they are not supposed to affect the sky.  They are aimed downwards and the city worked with the Lowell Observatory to be sure the new lights would not make the sky brighter.

 

Thanks for any ideas, Kent

I always assumed that it was the humidity that made the difference.

 

Living in a desert our relative humidity in summer time is around 10%-25% at night. In the winter, we end up with more moisture and the relative humidity jumps to 60-80% for the clear nights.

 

The city is converting all their streetlights to LED's over the next month. So I borrowed a meter and started taking nightly samples. So far with humidity in the 60% range it had NO EFFECT on sky darkness.

 

At higher humidities....well at 90% we just end up with fog. That has an effect on sky darkness.

 

I wonder if what the relationship is between transparency and dark sky. My skies are very transparent in summer and the sky "appears" darker. So far the meter is indicating that at the lower winter humidities of 60% my sky is just as dark as summer. It doesn't seem as dark, but I suppose the meter is more accurate than my eye.

 

I really think I need more samples to see how this works out. Fortunately, or unfortunately with the conversion happening next month I might have to wait one more year to get good samples.

 

I am going to buy a meter for myself. Interesting data.

 

Keep posting your observations. I am curious as to what you find.

 

BTW... I have spent three winters in Arizona about 40 miles east of Tucson. The last winter seemed much brighter than previous years. I did not have a meter with me.


Edited by vsteblina, 14 November 2018 - 02:33 PM.


#36 Kent10

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Posted 02 December 2018 - 10:22 PM

A quick update.

 

3 nights ago I had some great observing.  The sky looked very nice compared to recently so I measured.  20.95 SQM.  The next 2 days we received several inches of snow.  I went out tonight and the sky was noticeably brighter, 20.40 SQM.  It could be the snow on the ground or the humidity in the air or both but the difference is large for only 3 days separation.



#37 Tony Flanders

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Posted 03 December 2018 - 05:54 AM

I often wonder if loss of leaves affects very local light pollution in the winter months.
It's a bit of give and take I suppose.

Yes, in many areas I've measured a roughly 25% increase in skyglow when the leaves fall from the trees. The exact figure will depend on the nature of the surrounding lighting and how heavily wooded the areas near streetlights are.
 
There's a further increase when there's snow on the ground, which can be as much as 50% when the snow is fresh, and not fully plowed out below the lights.



#38 Kent10

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Posted 03 December 2018 - 08:57 AM

For my readings in post #36, the snow was fresh from earlier that day but they did plow.  Roads were still white in spots though.  Probably about 50/50 or so.  I went for a long walk earlier in the day.  Snow was still clean and fresh.



#39 Kent10

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Posted 05 December 2018 - 12:08 PM

As Jim said in post #9, the poor skies could be from the chimney smoke.  My readings were very low last night.  My wife and I went for a walk and you could see the smoke under every street light.  It was difficult to breathe.  The smoke must have an effect on the sky too.



#40 mikerepp

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Posted 05 December 2018 - 04:39 PM

I would kill for readings your getting.   Here at home, in the Chicago light dome I get readings of 16.5 to 17 at best!   I would like to point out that just because Flagstaff is an international dark city that doesn't mean that people are going to follow good dark practices.   Neighbors using bad outdoor lighting, flood lights that are meant to light up acres being used in backyards.   People that don't even use curtains or shades on their windows.   I have this in my neighborhood, never could understand why people would do that.  My two neighbors have no curtains or shades and leave every light on in the house.   Guess they like having people able to look in at them while they cook or watch TV.



#41 Kent10

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Posted 05 December 2018 - 04:45 PM

Mike, you are right about the lights in our neighborhoods.  Some are on all the time and they are very bright.  It always amazes me but I guess some don't appreciate the night sky we have or they feel safer with all their lights.  Or they like the looks of it on their house.  Some just forget.  It doesn't cost them much anyway.  My backyard neighbor had a fox or raccoon eat one of their chickens so now they keep their light on full time.  It has really affected my viewing but I bought something to block the lights and it works very well.  Cost me quite a bit but it is worth it.




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