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Are my skies actually darker in the winter?

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#1 Augustus

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Posted 20 September 2017 - 07:10 AM

At my house from April through September or October I can hardly see magnitude 4 stars with the naked eye on most nights. But in the fall/winter I can usually see magnitude 5 stars with a bit of effort, and magnitude 4.5 with ease - e.g. Orion's left arm.

 

Do a lot of people stay up later/have more lights on in the spring/summer or something? Do the leaves coming off the trees play a role?


Edited by Augustus, 20 September 2017 - 07:11 AM.


#2 SeymoreStars

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Posted 20 September 2017 - 07:22 AM

In NYS we have less humidity often during the winter, but the skies are not as steady.



#3 Richard O'Neill

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Posted 20 September 2017 - 07:36 AM

"Are my skies actually darker in the winter?"

 

 Mine seem to be, presumably due to lower humidity and more time for my eyes to adjust.



#4 trurl

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Posted 20 September 2017 - 07:43 AM

The end of astronomical twilight is much later in the summer also, so you need to be sure you make the comparison at the right time of the night.



#5 aatt

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Posted 20 September 2017 - 07:48 AM

I would say my skies are worse without leaves blocking the uplighting from the street lights. Skies are more transparent though, so there is a bit of a tradeoff.I forgot to mention the reflective aspect of snow.One more reason to hate it....


Edited by aatt, 20 September 2017 - 07:53 AM.


#6 trurl

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Posted 20 September 2017 - 07:51 AM

I would say my skies are worse without leaves blocking the uplighting from the street lights. Skies are more transparent though, so there is a bit of a tradeoff.

In my yard, leaves off the trees are the only way I can get a peek at a lot of the sky.grin.gif



#7 Redbetter

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Posted 20 September 2017 - 08:46 AM

Dry winter nights can indeed be very transparent.  This helps immensely in suburbia or the city.  The Milky Way becomes visible in the backyard when this happens. 



#8 Dark Night

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Posted 20 September 2017 - 09:04 AM

Mother Nature herself offers the sky observer in north temperate latitudes the two gifts of longest nights and a sky more transparent than usual.One reason for the clarity of a winter's night is that cold air cannot hold as much moisture as warm air can.  Hence, on many nights in the summer, the warm moisture-laden atmosphere causes the sky to appear hazier.  By day it is a milky, washed-out blue, which in winter becomes a richer, deeper and darker shade of blue.  For us in northern climes, this only adds more luster to that part of the sky containing the beautiful wintertime constellations. Indeed, it is seemingly nature's holiday decoration to commemorate the winter solstice and enlighten the long cold nights of winter.

 

*taken from https://www.space.co...ool-shapes.html



#9 George N

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Posted 20 September 2017 - 08:14 PM

My personal experience is that leaves off the trees - plus snow cover - makes winters brighter on nights of equal humidity. 

 

This summer, and even right now, the lack of transparency experienced along the Northern tier of states is caused by the smoke from the forest fires in the Western USA and Canada.



#10 treadmarks

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Posted 20 September 2017 - 09:16 PM

I've been noticing the same thing. I joined an astronomy club last February and visited their dark site. I was pretty impressed with the views there. Fast forward to this summer and I'm wondering why I even bother leaving the city. I'm pretty sure haze and humidity are to blame.



#11 BrooksObs

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Posted 21 September 2017 - 12:01 AM

At my house from April through September or October I can hardly see magnitude 4 stars with the naked eye on most nights. But in the fall/winter I can usually see magnitude 5 stars with a bit of effort, and magnitude 4.5 with ease - e.g. Orion's left arm.

 

Do a lot of people stay up later/have more lights on in the spring/summer or something? Do the leaves coming off the trees play a role?

 

It will depend heavily on just where you live in Connecticut. If it is a semi-urban area with plenty of lights, then the answer concerning conditions improving in winter will be a no. During the summer months the sky will be made darker because the leaves on the trees will block a considerable amount of the light pollution sources (the green grass helps, too). When the trees are bare, the degree of light pollution in the sky increases.

 

In rural areas the opposite to the above is true because of winter's decidedly lower relative humidity, clarity of the air plus being without troublesome area lighting. However, when the ground becomes covered with snow, if much in the way of light sources are present, sky conditions can deteriorate considerably.

 

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#12 Tony Flanders

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Posted 21 September 2017 - 06:10 AM

I have measured sky brightness at many locations across New York and New England. At all of them, the skyglow increases significantly -- ranging from about magnitude 0.3 in urban areas to about 0.1 in rural areas -- when the leaves are off the trees. Without exception, at all of these areas, skies are darkest during the summer months, when the foliage is full.

 

If you have perceived otherwise, it is probably because you were observing on nights of poor transparency. Those are common in the summer. Normally less so in September, but this particular September might be an exception; the summer weather has been lingering longer than usual. Early October is often best of all, with nearly full foliage on the trees coupled with excellent transparency.

 

Winter generally has brighter skies -- much brighter when there's fresh snow on the ground. There is an illusion that stars are easier to see, but that's because the winter skies have so many bright stars.



#13 pstarr

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Posted 21 September 2017 - 01:09 PM

My personal experience is that leaves off the trees - plus snow cover - makes winters brighter on nights of equal humidity. 

 

 

Mine too. Snow reflecting light upward makes the skies around me brighter. The loss of leaves lets lights be more visible from a distance.



#14 WoodyEnd

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Posted 21 September 2017 - 03:17 PM

Cities to my west are covered in fog much of the winter so my skies should be considerably darker but I do not have a meter to verify this.  



#15 SeymoreStars

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Posted 21 September 2017 - 04:41 PM

This was shot in the wintertime because the north pole (think Polaris) is bathed in sunlight much of the time and there is a noticeable glow to the north.
 
startrails


#16 BrooksObs

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Posted 21 September 2017 - 09:38 PM

 

This was shot in the wintertime because the north pole (think Polaris) is bathed in sunlight much of the time and there is a noticeable glow to the north.

 

If I understand the gist of your post, I'm afraid that your idea is physically impossible. Any glow seen toward the north, whether winter or summer, must originate with the source usually less than 100 miles distant from the observer. Regardless, the North Pole is in perpetual darkness during Northern Hemisphere midwinter.

 

BrooksObs



#17 SeymoreStars

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Posted 21 September 2017 - 10:19 PM

 

 

This was shot in the wintertime because the north pole (think Polaris) is bathed in sunlight much of the time and there is a noticeable glow to the north.

 

If I understand the gist of your post, I'm afraid that your idea is physically impossible. Any glow seen toward the north, whether winter or summer, must originate with the source usually less than 100 miles distant from the observer. Regardless, the North Pole is in perpetual darkness during Northern Hemisphere midwinter.

 

BrooksObs

 

Well then we agree to disagree.



#18 Tony Flanders

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Posted 22 September 2017 - 04:33 AM

 

 

 

This was shot in the wintertime because the north pole (think Polaris) is bathed in sunlight much of the time and there is a noticeable glow to the north.

 

If I understand the gist of your post, I'm afraid that your idea is physically impossible. Any glow seen toward the north, whether winter or summer, must originate with the source usually less than 100 miles distant from the observer. Regardless, the North Pole is in perpetual darkness during Northern Hemisphere midwinter.

 

BrooksObs

 

Well then we agree to disagree.

 

This has been studied both analytically and with measurements; there's no room for disagreement.

 

BrooksObs is correct that artificial light pollution has only a modest effect 100 miles from the source, and no measurable effect 200 miles from the source. This was explored decades ago in a classic paper by R. H. Garstang.

 

The Sun, being much brighter than any artificial light pollution, and illuminating the atmosphere top down rather than bottom up, is visible from greater distances. The classic definition of astronomical twilight states that the glow of sunlight disappears when the Sun is 18 degrees below the horizon. That means that the closest spot in direct sunlight is 18 * 60 nautical miles away, which is 1,243 statute miles. That's a long way, but nowhere near the distance from Pennsylvania to the arctic.

 

So any glow to the north around midnight in summer around latitude 40N is not due to diffused sunlight. It might be due to artificial light pollution, airglow, or the aurora.



#19 trurl

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Posted 22 September 2017 - 07:34 AM

 

 

This was shot in the wintertime because the north pole (think Polaris) is bathed in sunlight much of the time and there is a noticeable glow to the north.

 

If I understand the gist of your post, I'm afraid that your idea is physically impossible. Any glow seen toward the north, whether winter or summer, must originate with the source usually less than 100 miles distant from the observer. Regardless, the North Pole is in perpetual darkness during Northern Hemisphere midwinter.

 

BrooksObs

 

Also, no room for disagreement here either. People living above the arctic circle can attest to the darkness of winter.

 

I am surprised there is any confusion about this.



#20 Phillip Creed

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Posted 22 September 2017 - 11:28 AM

I have measured sky brightness at many locations across New York and New England. At all of them, the skyglow increases significantly -- ranging from about magnitude 0.3 in urban areas to about 0.1 in rural areas -- when the leaves are off the trees. Without exception, at all of these areas, skies are darkest during the summer months, when the foliage is full.

 

If you have perceived otherwise, it is probably because you were observing on nights of poor transparency. Those are common in the summer. Normally less so in September, but this particular September might be an exception; the summer weather has been lingering longer than usual. Early October is often best of all, with nearly full foliage on the trees coupled with excellent transparency.

 

Winter generally has brighter skies -- much brighter when there's fresh snow on the ground. There is an illusion that stars are easier to see, but that's because the winter skies have so many bright stars.

I'd concur with these measurements.  I notice about a 0.2-mag drop in NLM during the winter months vs. the summer months, with October being the best blend of transparency, reasonable odds of clear skies, temperatures and length of night.

Clear Skies,

Phil



#21 csrlice12

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Posted 24 September 2017 - 11:27 AM

What does it matter.....don't let just good skies stop you from getting out.  Viewing in "meh" conditions beats not viewing.   And I've had "meh" nights when all of a sudden the sky opens up in all its splendor. 



#22 Arcticpaddler

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Posted 03 October 2017 - 08:30 PM

If there is any light pollution that impacts your sky (like a big city within 100-120 miles or a small town within 20 miles) there will be enough reflection off of the snowpack to brighten your sky for sure.  Even yard lights will impact the sky--a big reason why much of rural America is no longer truly dark.  On the other hand, a natural sky will hardly be affected at all by snow.  A few years ago I was camped in the middle of a frozen lake in far NE Minnesota in early March  (Bortle 1-2 skies).  The Zodiacal Light was yellow and extended far across the sky, no trace of light domes occurred in any direction, and the only terrestrial illumination at all was from starlight.  A bit disorienting.


Edited by Arcticpaddler, 03 October 2017 - 08:32 PM.


#23 Stargazer713

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Posted 07 October 2017 - 03:51 PM

I know mine are definately darker.  I believe it's due to less humidity and particles it the atmosphere. Water vapor can reflect light adding to the pollution. On clear dry cold fall/winter nights I can see a full 1- 11/2 mag more stars.



#24 BrooksObs

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Posted 07 October 2017 - 04:32 PM

I know mine are definately darker.  I believe it's due to less humidity and particles it the atmosphere. Water vapor can reflect light adding to the pollution. On clear dry cold fall/winter nights I can see a full 1- 11/2 mag more stars.

I'm afraid that this situation must result from just how badly your local skies are impacted by light pollution to begin with! It would only be as the result of lowering atmospheric humidity that they could appear darker in autumn/winter. However, I think that the sky grows far worse any time snow happens to be on the ground.

 

BrooksObs



#25 penguinx64

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Posted 10 October 2017 - 12:01 PM

When I lived in Holland, my skies were darker in the winter too.




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