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General Astronomy => Light Pollution Topics => Topic started by: calfkommomu on December 25, 2017, 09:22:46 AM

Title: Mostly Clear vs Clear
Post by: calfkommomu on December 25, 2017, 09:22:46 AM
When you reside in a light polluted area it is an issue.  Here are two pictures of similar vulnerability, one with a mainly clear skies based on most of the weather websites I visit, and one completely apparent.  You can see that 5 percent or less of all cloud opacity can considerably bounce the light back at you.Attached Thumbnails
(https://s10.postimg.org/kca2y1p39/0_attachment_00.jpg) (https://postimg.org/image/kca2y1p39/)

(https://s10.postimg.org/419z1r7gl/0_attachment_01.jpg) (https://postimg.org/image/419z1r7gl/)
Title: Re: Mostly Clear vs Clear
Post by: vieproltesro on December 27, 2017, 03:08:43 PM
Wow! Something for me to try... You could actually determine how different conditions affect observing, like humidity.
Title: Re: Mostly Clear vs Clear
Post by: Cesar Lawhorn on December 28, 2017, 12:02:48 AM
On Earth, no such thing as completely clear.

Maybe on the Moon.
Title: Re: Mostly Clear vs Clear
Post by: agtofonist on December 30, 2017, 11:32:18 AM
Quote
On Earth, no such thing as completely clear.

Maybe on the Moon.

Definition of completely clear: I see no clouds, there are no clouds

In other words: there are clouds, but I don't see them, so they don't exist.
Title: Re: Mostly Clear vs Clear
Post by: teirazaro on December 30, 2017, 01:50:58 PM
Yes, it makes a huge difference as your images show and I only do visual observing. Even for solar the impact is heavy.
Title: Re: Mostly Clear vs Clear
Post by: reobladvasys on January 08, 2018, 01:52:47 PM
Quote
Quote

On Earth, no such thing as completely clear.

Maybe on the Moon.

Definition of completely clear: I see no clouds, there are no clouds

In other words: there are clouds, but I don't see them, so they don't exist.
It's just before twilight. I have seen no clouds during the night. Twilight increases and now the sunlight illuminates some high clouds that somehow miraculously appeared in the last few minutes.

In other news....
Title: Re: Mostly Clear vs Clear
Post by: Matthew Danielson on January 09, 2018, 07:29:11 PM
Quote
It's just before twilight. I have seen no clouds during the night. Twilight increases and now the sunlight illuminates some high clouds that somehow miraculously appeared in the last few minutes.

In other news....
Don't worry, the night's over and there's no more observing to do.
Title: Re: Mostly Clear vs Clear
Post by: flasattecof on January 09, 2018, 08:00:05 PM
Quote
Quote

It's just before twilight. I have seen no clouds during the night. Twilight increases and now the sunlight illuminates some high clouds that somehow miraculously appeared in the last few minutes.

In other news....
Don't worry, the night's over and there's no more observing to do.
http://www.solarastronomy.org/ (http://www.solarastronomy.org/)
Title: Re: Mostly Clear vs Clear
Post by: synchanrimyp on January 10, 2018, 05:36:27 PM
Quote
Quote

Quote

It's just before twilight. I have seen no clouds during the night. Twilight increases and now the sunlight illuminates some high clouds that somehow miraculously appeared in the last few minutes.

In other news....
Don't worry, the night's over and there's no more observing to do.
http://www.solarastronomy.org/ (http://www.solarastronomy.org/)
Uhh....

Go to sleep, you need it. It'll help you as you wait for it to get near the meridian.
Title: Re: Mostly Clear vs Clear
Post by: ziecouvicog on January 10, 2018, 06:48:48 PM
Quote
Quote

It's just before twilight. I have seen no clouds during the night. Twilight increases and now the sunlight illuminates some high clouds that somehow miraculously appeared in the last few minutes.

In other news....
Don't worry, the night's over and there's no more observing to do.
http://www.solarastronomy.org/ (http://www.solarastronomy.org/)[/quote]
Uhh....

Go to sleep, you need it. It'll help you as you wait for it to get near the meridian.[/quote]
http://www.collectiv...-is-not-needed/ (http://www.collective-evolution.com/2013/07/13/alternative-sleep-cycles-7-10-hours-is-not-needed/)
Title: Re: Mostly Clear vs Clear
Post by: David Lipson on January 12, 2018, 05:26:20 AM
Still need to wait for it get near the meridian.
Title: Re: Mostly Clear vs Clear
Post by: redoroto on January 12, 2018, 07:44:59 AM
Quote
Still need to wait for it get near the meridian.

Everyone's observing site and micro-climates are a little bit different. By noon the Sun will have heated up the atmosphere and the ground.
Title: Re: Mostly Clear vs Clear
Post by: naiciareamu on January 12, 2018, 12:11:34 PM
The difference between those two images does not derive from the presence or lack of cloud outside the frame. It results from the difference in the quantity of water vapor and/or pollutants. Under a clean atmosphere, between any clouds which might be hanging about the sky will nonetheless be nice and dark as allowed by light pollution. In other words, sucker holes in a clean airmass are far better than a cloudless but 'dirty' airmass, as regards transparency and sky darkness.
Title: Re: Mostly Clear vs Clear
Post by: inuninab on January 13, 2018, 05:51:15 AM
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The difference between those two images does not derive from the presence or lack of cloud outside the frame. It results from the difference in the quantity of water vapor and/or pollutants. Under a clean atmosphere, between any clouds which might be hanging about the sky will nonetheless be nice and dark as allowed by light pollution. In other words, sucker holes in a clean airmass are far better than a cloudless but 'dirty' airmass, as regards transparency and sky darkness.

I see more stars in the upper photo than in the lower photo.
Title: Re: Mostly Clear vs Clear
Post by: Adam Rice on January 18, 2018, 12:08:25 AM
https://en.wikipedia.org/wiki/Cloud (https://en.wikipedia.org/wiki/Cloud)
<p class="citation">Quote

I see more stars in the upper photo than in the lower photo.
[/quote]
I have to disagree with you perhaps your eyesight is not very keen, but if you look at the lower photo you can see crisp dots of starlight, some barely as bright as the background sky, but in the upper photo, merely some smears of the brighter ones.
Title: Re: Mostly Clear vs Clear
Post by: ulpehaco on January 18, 2018, 12:57:40 AM
Quote
https://en.wikipedia.org/wiki/Cloud (https://en.wikipedia.org/wiki/Cloud)
<p class="citation">Quote

I see more stars in the upper photo than in the lower photo.
I have to disagree with you perhaps your eyesight is not very keen, but if you look at the lower photo you can see crisp dots of starlight, some barely as bright as the background sky, but in the upper photo, merely some smears of the brighter ones.

[/quote]
If I say I see more stars in the "brown" photo than in the "blue" photo, you will have to take my word for it. Have you actually compared the photos diligently?
Title: Re: Mostly Clear vs Clear
Post by: Marlin Riewer on January 18, 2018, 06:21:45 AM
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If I say I see more stars in the "brown" photo than in the "blue" photo, you will have to take my word for it. Have you actually compared the photos diligently?
Let me tell you that I have the original 6000x4000 pixel images on my computer and I have zoomed in close and there are more stars no doubt. If you need more proof here are two close ups of mizar. And I was wrong, the exposure for the second photo was only 10 seconds because of the brightness. The third image is a 30 second exposure on the same night I just lowered the brightness to tone down the trailing. I'm not sure what you're trying to deny here but either way there are more darker stars when there are less clouds it is obvious there are either clouds or other pollutants or whatever.

Is this seriously what you do all day going around telling people that there are more stars with more clouds???????

Even if you were somehow magically right, I'd prefer less yellow glow for less stars even though that's not how it works.Attached Thumbnails
(https://s10.postimg.org/wi8731nf9/16_attachment_01.jpg) (https://postimg.org/image/wi8731nf9/)

(https://s10.postimg.org/vspeqp2b9/16_attachment_02.jpg) (https://postimg.org/image/vspeqp2b9/)
Title: Re: Mostly Clear vs Clear
Post by: kocewaffre on January 20, 2018, 06:41:03 PM
bunny, the first images you posted, I have to agree that I detected more stars in the brown sky version as well. That you're looking at the original makes it an apples and oranges comparison. Perhaps our perception is skewed by the fact that there are more bright stars in the muddy one you posted for our review.. (I just looked at what was on page, I didn't open either)
Title: Re: Mostly Clear vs Clear
Post by: inuninab on January 21, 2018, 08:08:11 AM
ok ok ok ok ok ok ok ok ok ok ok ok whatever

My image's fault.

But that doesn't skew the fact that clouds reflect the light pollution better that's the point of this thread not counting stars if I get this kind of harassment for just showing something to people why don't I not post anything and keep everyone less educated?
Title: Re: Mostly Clear vs Clear
Post by: Gandza Startley on January 26, 2018, 01:55:58 AM
Quote
ok ok ok ok ok ok ok ok ok ok ok ok whatever

My image's fault.

But that doesn't skew the fact that clouds reflect the light pollution better that's the point of this thread not counting stars if I get this kind of harassment for just showing something to people why don't I not post anything and keep everyone less educated?

You posted two images initially and of those two images, the one which we were supposed to think to be inferior actually showed more stars. What the "originals" showed was not important because you did not provide those originals.

Mine was simply an honest comment based on what could be seen in those two images, as presented. But I didn't insult anyone, their eyesight or their powers of observation by making that statement.
Title: Re: Mostly Clear vs Clear
Post by: Carl Hanks on January 31, 2018, 08:22:28 AM
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Is this seriously what you do all day going around telling people that there are more stars with more clouds???????
Now where did I say anything even remotely like that?
Title: Re: Mostly Clear vs Clear
Post by: John Sanchez on January 31, 2018, 09:06:59 AM
You're fine bunnyraptor. No one is criticizing you. Yes, your point is overall valid. There is a big difference between clear and hazy sky. Hazy skies make imaging and observing difficult. You are absolutely correct.
Title: Re: Mostly Clear vs Clear
Post by: colzefuli on January 31, 2018, 12:29:41 PM
whatever i'm done with this thread
Title: Re: Mostly Clear vs Clear
Post by: contpeeresto on February 02, 2018, 03:39:13 PM
What you're talking about is transparency. Dust, smoke and humidity reduce the amount of light getting through from outside the atmosphere and reflect light pollution. In places with negligible light pollution, the sky is black on a good night. The only way you can tell that there are clouds overhead is that stars are missing. On bad nights, the sky is visibly gray.
Title: Re: Mostly Clear vs Clear
Post by: revekosque on February 02, 2018, 05:09:04 PM
I don't understand this thread yet, is it about clouds and no clouds?
Also for that original images, is it taken from different times so one is almost clear but light polluted and the other is when the sky is clear or no light polluted? I mean how come for one location to go from LP to no LP unless all lights turned off?? 
I view the sky since years, and there are times when I see the sky better visual than other times for same location.
Title: Re: Mostly Clear vs Clear
Post by: unverjacea on February 03, 2018, 06:45:20 AM
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Here are 2 pictures of similar exposure, one with a mostly clear sky according to most of the weather websites I go to, and one completely clear.
What do you mean by "similar exposures?" I find it extremely hard to believe that transparency is the main difference between the two photos.The first is obviously a much longer exposure, showing many more faint stars. That's presumably why the pink light pollution is so prominent.The second (presumably taken with a wide-angle lens, since the Big Dipper is small in it) is dominated by the blue either of scattered sunlight or scattered moonlight. It must have been taken either near full Moon or in early twilight. The natural blue cast is much stronger than the artificial pink glow.
Title: Re: Mostly Clear vs Clear
Post by: stunfalriave on February 04, 2018, 12:37:24 PM
Quote
I don't understand this thread yet, is it about clouds and no clouds?
Also for that original images, is it taken from different times so one is almost clear but light polluted and the other is when the sky is clear or no light polluted? I mean how come for one location to go from LP to no LP unless all lights turned off??
I view the sky since years, and there are times when I see the sky better visual than other times for same location.

Light pollution happens because of the scattering of artificial light by dust and moisture in the atmosphere, as well as by the atmosphere itself. Even clean air scatters light.

Blue light scatters more, so a natural sky should appear blue, day or night. Artificial light tends toward the yellow and red so that long exposures appear discolored, not blue.
Title: Re: Mostly Clear vs Clear
Post by: Tye Paez on February 08, 2018, 11:52:46 PM
Quote
Quote
Here are 2 pictures of similar exposure, one with a mostly clear sky according to most of the weather websites I go to, and one completely clear.

What do you mean by "similar exposures?" I find it extremely hard to believe that transparency is the main difference between the two photos.
The first is obviously a much longer exposure, showing many more faint stars. That's presumably why the pink light pollution is so prominent.
The second (presumably taken with a wide-angle lens, since the Big Dipper is small in it) is dominated by the blue either of scattered sunlight or scattered moonlight. It must have been taken either near full Moon or in early twilight. The natural blue cast is much stronger than the artificial pink glow.
In the absence of artificial light, a long exposure photo of the sky will tend to stay blue even without moonlight or twilight. The characteristics of the film or sensor also throw in their effects on the image.
Title: Re: Mostly Clear vs Clear
Post by: exjeraca on February 09, 2018, 03:29:10 AM
I see.

Yes, there are things that make it worse, i did say in a light pollution topic somewhere [here or another site] that our haze or humidity and maybe dust and heat all amplify or magnify the light pollution, i think your topic is the best explanation of what i was meaning.

Good that you can get stars even if the sky isn't clear, but not cloudy ofcourse, in my country the sky is clear because no cloud, but i should say or call it, not clean sky, and not clean means it is polluted, pollution is a bad word and it is nearly opposite of the clean meaning, so sky is clear but not clean, that is why in winter here i feel the glow is less and clarity is better because i think the atmosphere is cleaned by rain and no humidity and no dust, can't wait it.
Title: Re: Mostly Clear vs Clear
Post by: Jeff Jubenville on February 09, 2018, 05:35:55 AM
Listen the reason why the first image is more yellow isn't because of a longer exposure I took a longer exposure on the same night as the second photo and it looked like this, clearly the light pollution is tending to less yellow and the reason why the first one is yellow is because there were more clouds I could seeeeeeee them.
Attached Thumbnails
(https://s13.postimg.org/40olbj1s3/29_attachment_00.jpg) (https://postimg.org/image/40olbj1s3/)
Title: Re: Mostly Clear vs Clear
Post by: Rick Reiter on February 09, 2018, 06:06:07 AM
Photos aside, the point is that even if you're going after DSO, sky conditions (transparency) can make a big difference, just like seeing with planets. Sometimes, even if there's no "clouds" as such, there is a thin layer of mist or haze that substantially reduces visibility. Similarly, on nights like those dewing also seems to be a bigger problem.

For this reason I try to plan my dark site trips for only the most pristine, transparent nights. As Glenn mentioned, air pollution can be a serious problem with light pollution, so it's extra good if I can observe after a recent storm cleans out the atmosphere. It's all about memorable views for me, and mediocre nights tend to produce mediocre views.
Title: Re: Mostly Clear vs Clear
Post by: Noty Tarabori on February 09, 2018, 08:44:31 AM
Quote
Listen the reason why the first image is more yellow isn't because of a longer exposure I took a longer exposure on the same night as the second photo and it looked like this, clearly the light pollution is tending to less yellow and the reason why the first one is yellow is because there were more clouds I could seeeeeeee them.

Of the images shown in the first post, the first one, with the brown background, showed more stars. One cannot make comments on other images which you did not present.

That dirt, clouds and moisture in the atmosphere degrade the views, especially when light pollution is present, has long been known.