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Why is my sky so bright?

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#1 Kent10

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Posted 09 November 2018 - 01:08 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



#2 Kent10

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Posted 09 November 2018 - 01:20 PM

It could be from the fires out in CA.  Is the smoke coming this way, I don't know.  I don't smell any smoke but we have also had some prescribed burns and that could be it.  Again I don't smell it.  Also, there are a lot of fireplaces burning wood in my area.  I wonder if that affects the whole sky?  It was cold yesterday but not so cold the previous few days so I am not sure that is it.


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#3 junomike

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Posted 09 November 2018 - 01:40 PM

People may have their lights on longer as well as maybe fireplaces/wood burning stoves which might put more particulates into the atmosphere.


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#4 TOMDEY

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Posted 09 November 2018 - 02:28 PM

Hmmm... Well, even lights that point where intended, the illumination will bounce back up into the sky, depending on the albedo of the ground etc. And most newer lighting is (alas) that nefarious, pernicious, white LD... most always brighter and bluer than the older stuff.

 

Ironically, I live in New York (?!) and average SQM for me is 21.3+ (21.0-21.8, depending on the night and conditions). This is "upstate" in a rural pocket or relative OK sky.

 

I designed LPS street lights back in the 1980s. They worked GREAT, but the U.S.A. wanted no part of it, because people whined about the yellow color making their clothes and cars look "unnatural." But LPS were very popular in Europe. So now, we illuminate the night with white LEDs, bright as day... because so our cars and shoes look "natural." Marketing, 100% marketing.  Tom


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#5 Keith Rivich

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Posted 09 November 2018 - 02:54 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

Here is one site that may have an answer:

https://www.ssec.wis...tellite=goes-16

 

In the channel selection look at 8, 9 and 10 which are upper, mid-level and lower level water vapor channels. The lower level shows pretty dry air but as you increase in altitude the air is increasingly more humid. Hence brighter skies. 


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#6 Kent10

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Posted 09 November 2018 - 03:16 PM

Thanks very much Keith.  Looking at the upper level it doesn't look clear anywhere in the US.  I'll have to keep an eye on this map and if and when I do get a better sky, see if the map looks different.

 

I checked some smoke maps and it doesn't appear any smoke is affecting my area.  I used this site and others too  https://www.astrospheric.com/?Loc=Map  If I advance the time, however, it does look like some smoke moves quite close to me in the evening.  I can't check previous days but I am going to check tonight to see if any smoke is on my map and test my sky again to see what readings I get.



#7 Kent10

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Posted 09 November 2018 - 03:25 PM

Hmmm... Well, even lights that point where intended, the illumination will bounce back up into the sky, depending on the albedo of the ground etc. And most newer lighting is (alas) that nefarious, pernicious, white LD... most always brighter and bluer than the older stuff.

 

Ironically, I live in New York (?!) and average SQM for me is 21.3+ (21.0-21.8, depending on the night and conditions). This is "upstate" in a rural pocket or relative OK sky.

 

I designed LPS street lights back in the 1980s. They worked GREAT, but the U.S.A. wanted no part of it, because people whined about the yellow color making their clothes and cars look "unnatural." But LPS were very popular in Europe. So now, we illuminate the night with white LEDs, bright as day... because so our cars and shoes look "natural." Marketing, 100% marketing.  Tom

You make a very good point, Tom, about the light reflecting back into the sky.  And when it snows it will probably be worse.  These new lights are LEDs and they are much brighter than what we had.  They look orange.  I think at least in Flagstaff they avoided the white ones but I still don't like them when we go for walks in our neighborhood at night they are so bright even from a distance.

 

I will have to keep taking readings for months and if I never get my 21.2 readings back, I am going to talk to the director at Lowell and also the city.  I have been in touch with both already as they put these new lights up.



#8 Kent10

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Posted 09 November 2018 - 03:27 PM

People may have their lights on longer as well as maybe fireplaces/wood burning stoves which might put more particulates into the atmosphere.

Neighborhood lights are always a problem.  I don't know if they are worse now than a few months ago.  No Christmas lights up yet but maybe when they are put up people will use those instead of their other bright lights, so perhaps better?  I have always wondered about the fireplaces and what I am breathing as I observe too.



#9 rockethead26

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Posted 09 November 2018 - 06:00 PM

Kent,

 

I'm pretty sure it's smoke from wood stoves and fireplaces. The southeast sky from my otherwise dark backyard has almost no stars visible and that part of the sky coincides with the Flagstaff light dome. This has happened in winter before on calm dry nights.



#10 Starman1

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Posted 09 November 2018 - 06:07 PM

I was just at a 3 night star party with low relative humidity (under 30% all night), but almost totally clouded out due to high cirrus.

Humidity on the ground is not an indicator of transparency, and nor is the water vapor maps.

You need to combine water vapor with visible to get a true view of what's there.

Right now, my locale shows dry air but the atmosphere indicates mediocre transparency, and I have no smoke from the fires in my local air.

 

The best skies, for me, are when the air is very very dry and cloudless at all altitudes and I am at high altitude.

Those 3 things seem to happen at the same time about once a year.



#11 Kent10

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Posted 09 November 2018 - 06:09 PM

Hi Jim,

 

I was just thinking about talking to you about this.  I have been out the last several night starting Monday and measured the sky with my SQM.  One night was slightly higher maybe 20.8 but the other nights 20.7.  Last night was cold and I thought there probably were lots of stoves going.  But the previous nights were on the warm side.  Still, I suppose many stoves could have been used.  I keep my house at 58 to save money for scopes smile.gif .  I just dress warmly inside the house.  You get used to it.

 

Do you think with these brighter lights we have now that they are reflecting more light into the sky?  I hope not.  In that case we have to really hope for the intersection only lights, but that would only be in some neighborhoods. 

 

I am going to keep checking the sky with my SQM over time to see if I get my 21.1 sky back.  I have had slightly higher but 21.1 is about the darkest I was getting regularly but certainly not all the time.  Out in Doney Park I read 21.3 and at the GC 21.6.  Also, just a few minutes north of me 21.6.  I should take my scopes out there but it is so easy to view from my backyard when I am so busy.  I look forward to the day I can get to a darker sky.

 

Yes, the southeast looking towards the city has always been pretty bright.  I have wondered if that gets better after midnight but with my work, I never view past midnight.

 

Thanks Jim.


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#12 Kent10

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Posted 09 November 2018 - 06:13 PM

I was just at a 3 night star party with low relative humidity (under 30% all night), but almost totally clouded out due to high cirrus.

Humidity on the ground is not an indicator of transparency, and nor is the water vapor maps.

You need to combine water vapor with visible to get a true view of what's there.

Right now, my locale shows dry air but the atmosphere indicates mediocre transparency, and I have no smoke from the fires in my local air.

 

The best skies, for me, are when the air is very very dry and cloudless at all altitudes and I am at high altitude.

Those 3 things seem to happen at the same time about once a year.

Thanks Don.  The Clear Sky Chart is showing the highest transparency and 0 cloud cover tonight.  I don't rely on this site but I like to look at it.  Seeing is only average tonight.  Last night it was terrible and the chart indicated it was terrible so it did get that right.



#13 Migwan

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Posted 09 November 2018 - 08:39 PM

Same satellite, different site.   It is showing a lot of upper water vapor.  Didn't check mid or lower, but with that much showing, mid will likely be effected too. 

 

Edit.  The mid level pretty dry (warm).   To read the IR views look for colder temps (color key below map).  Tonight your area is within a large swatch of dark blue area (which is quite warm) that stretches across the land.  However if you look close there is a swatch within that centered just to your west.  Easy to miss but its green which is below -54 (quite cold).  Warm to cold without other temps in between and not showing in the mid level, likely represents Cirrus or similar.    Of course this may all change by tomorrow. 

 

The night time view on the home page is an overall IR and shows thin clouding centered to the N of Flafstaff as of midnight.   By the way the lights of Flagstaff are somewhat better than might be expected, but they are there.

 

https://www.star.nes...nd=08&length=24

 

Here is site home.  This site works easiest to expand on tablet or phone.  On computer push pause and then click on map. 

 

https://www.star.nes...COLOR&length=24

 

There is a GOES west satellite feed that would give you an even better look.  jd


Edited by Migwan, 10 November 2018 - 12:02 AM.


#14 rockethead26

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Posted 10 November 2018 - 12:16 AM

Hi Jim,

 

I was just thinking about talking to you about this.  I have been out the last several night starting Monday and measured the sky with my SQM.  One night was slightly higher maybe 20.8 but the other nights 20.7.  Last night was cold and I thought there probably were lots of stoves going.  But the previous nights were on the warm side.  Still, I suppose many stoves could have been used.  I keep my house at 58 to save money for scopes smile.gif .  I just dress warmly inside the house.  You get used to it.

 

Do you think with these brighter lights we have now that they are reflecting more light into the sky?  I hope not.  In that case we have to really hope for the intersection only lights, but that would only be in some neighborhoods. 

 

I am going to keep checking the sky with my SQM over time to see if I get my 21.1 sky back.  I have had slightly higher but 21.1 is about the darkest I was getting regularly but certainly not all the time.  Out in Doney Park I read 21.3 and at the GC 21.6.  Also, just a few minutes north of me 21.6.  I should take my scopes out there but it is so easy to view from my backyard when I am so busy.  I look forward to the day I can get to a darker sky.

 

Yes, the southeast looking towards the city has always been pretty bright.  I have wondered if that gets better after midnight but with my work, I never view past midnight.

 

Thanks Jim.

I was out Monday night when I noticed the smoke and again on Tuesday and Wednesday when I went out just to take a look. I can smell the neighborhood smoke tonight. I'm rarely out after midnight either. I see the new LEDs as putting more light on the ground, so contrary to what we were told, it seems more light should be reflected up off the pavement. I'm probably wrong, though.



#15 Starman1

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Posted 10 November 2018 - 01:43 AM

Blue is most effectively scattered by the atmosphere.

LEDs emit a lot more blue light, hence cause more sky glow due to scatter.

Los Angeles, at 100 miles away, has gotten 0.2 magnitudes brighter in just the last 5 years because of the conversion.

You might try this for clouds at multiple altitudes:

https://www.windy.co....086,-118.490,6

and

https://www.meteoblu...-states_5383225

You can enter your own locations in both charts.



#16 Jeff B1

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Posted 10 November 2018 - 08:35 AM

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

Football season makes school ball fields light up the Universe.



#17 precaud

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Posted 10 November 2018 - 08:59 AM

Football season makes school ball fields light up the Universe.

 

That is really true here. In football season the park two blocks away leaves the stadium lights on every night until 9-10pm, even when it is not being used... yuk. Calls to the city Parks and Rec dep't have gone unreturned.



#18 John Rogers

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Posted 10 November 2018 - 09:54 AM

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

 

John Rogers


Edited by John Rogers, 10 November 2018 - 10:09 AM.


#19 gdd

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Posted 10 November 2018 - 11:15 AM

Are you doing all of your measurements at the darkest time of night? Now that it gets dark earlier with winter approaching people are still active when it is dark outside.

 

Gale



#20 Kent10

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Posted 10 November 2018 - 01:16 PM

Are you doing all of your measurements at the darkest time of night? Now that it gets dark earlier with winter approaching people are still active when it is dark outside.

 

Gale

Hi Gale,

 

I don't specifically look at the time but I measure several times around the same time 10 to 11 pm.  I bet it would get darker after midnight but I am not viewing then to measure.  I could try to measure before I go to bed which is after midnight.  I am trying to be consistent in my results.  Last night was 20.7 up to 20.8 or so.  I also measure several areas of the sky and try to avoid the Milky Way which would give a brighter reading.



#21 Kent10

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Posted 10 November 2018 - 01:24 PM

The reason I started using my SQM this last week is because the sky seemed brighter than it usually does for me at new moon time.  I am sure it varies throughout the seasons and I am going to keep checking.  I don't have any football fields too close to me.  I wonder if the bright lights they use are better than in other cities because Flagstaff has rules being an International Dark Sky City.

 

Don, thanks for the links.

 

Jim, I don't like the smoke either.  I also wonder how it affects the seeing.  Our neighbors burn wood constantly even when it is quite warm out.  When the snow arrives then we might get some brighter reflections into the sky from these new lights.  I'll have to take more readings and compare. 



#22 Starman1

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Posted 10 November 2018 - 01:41 PM

Note that the SQM-L usually gets darker readings than the SQM if the Milky Way is avoided.  The only time the SQM-L might read brighter than the SQM

is if it is pointed at the Milky Way.

As one example: when the MW is on the horizon and the north galactic pole is straight up, the SQM-L reads close to 0.3 magnitudes darker than the SQM.

The smaller the field surveyed, the greater the discrepancies can be,

 

The only point here is to always mention whether you are taking readings with an SQM or an SQM-L, because the readings are not directly comparable.



#23 Kent10

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Posted 10 November 2018 - 01:52 PM

I do have the narrow FOV SQM-L.  I measure several times and several areas of the sky, usually near zenith and avoiding the Milky Way to get as dark a reading as I can.


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#24 Starman1

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Posted 10 November 2018 - 02:45 PM

Then the sky may actually be brighter than you're measuring.

Try taking one reading at a 45° altitude N-S-E-W and another at the zenith and average them.

That will give you a better idea of the brightness of the overall sky and, in the process, tell you what part of the sky to look for the faintest objects in.



#25 Kent10

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Posted 11 November 2018 - 11:47 AM

I took a reading after midnight, last night, and it was slightly darker at 20.8 maybe 20.85 averaging several readings.  Don, I have trees around the back yard so I might be able to get some readings at 45 degrees but not in all directions.  I do realize that the readings I am taking are the best/darkest I can get and that my overall sky is not that dark.  I am trying to be consistent though in my comparisons from night to night and over the seasons.  The 20.8 I got last night after midnight is still a lot less than my best 21.15 - 21.2.

 

Actually, I just checked my notes and I have gotten a reading of 21.25-21.27 at my house once.  That was in July.  Several times I had the 21.15-21.2 readings and I see it is in the late spring and summer.  I have had lower readings in the winter before.  If I don't get the higher readings this summer then I will assume these new lights are having an impact.  I do wish I could get darker readings in the winter though.  It could be all the smoke from stoves and fireplaces.




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