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High transparency makes such a big difference

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#26 Arcticpaddler

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Posted 23 August 2019 - 11:32 AM

 

The best indicator for me is how much scatter I see when the sun is about an hour away from setting. If the western sky behind my tree line is an obvious rich blue color, I know I'm going to have a great night. If it has a dull blue, almost pewter-like color, I'll have a good, but not great night. If it's almost white-washed and doesn't turn blue again until you're 90 degrees away from the sun, it's going to be a poor night (though typically the seeing will be very good on those nights).

This is my indicator as well.  If I can see M33 and M92 with the naked eye without much difficulty I know I have a good night.

 

Transparency is a tricky thing.  Sometimes the lower levels of that atmosphere are crystal clear, and I can look 30-50 miles across the western arm of Lake Superior and see no haze, while up high smoke from distant wildfires makes the sky a milky blue and the sunset red.

 

I've seen the opposite true as well while observing from over 10,000 feet in the Rockies.  Smoke and haze down low, transparent above.

 

With a truly transparent atmosphere, altitude matters very little.  A friend of mine spent a few days on a boat off Indonesia last month and had one of the best views of the Milky Way he's ever seen--and we both live under Bortle 3 skies.


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#27 Starman1

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Posted 23 August 2019 - 12:06 PM

This is my indicator as well.  If I can see M33 and M92 with the naked eye without much difficulty I know I have a good night.

 

Transparency is a tricky thing.  Sometimes the lower levels of that atmosphere are crystal clear, and I can look 30-50 miles across the western arm of Lake Superior and see no haze, while up high smoke from distant wildfires makes the sky a milky blue and the sunset red.

 

I've seen the opposite true as well while observing from over 10,000 feet in the Rockies.  Smoke and haze down low, transparent above.

 

With a truly transparent atmosphere, altitude matters very little.  A friend of mine spent a few days on a boat off Indonesia last month and had one of the best views of the Milky Way he's ever seen--and we both live under Bortle 3 skies.

Right, there.  I've watched Omega Centauri set below the ground fully resolved in super transparent skies.

Most of the time, all the faint stars disappear well above the horizon.

[poor view compared to Australia, but then, we get what we can, eh?]


Edited by Starman1, 23 August 2019 - 12:07 PM.

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#28 ChristopherBeere

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Posted 23 August 2019 - 01:50 PM

Of course as the transparency increases and the extinction decreases the airglow becomes a real problem.

 

My best night in the Kalahari (at 5200ft) was -3c with zero humidity and yielded 22.05 on the SQM at 03:30 when the galaxy set. Earlier in the evening when the galaxy was culminating the airglow was obscuring over 100 degrees of lateral horizon south/southeast and well over 30 degrees of altitude.

 

 

A shot from that night illustrating it :

 

Southern-Pole.png

 

 

You can clearly see the airglow as high as the SMC.


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#29 Astrojedi

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Posted 23 August 2019 - 02:32 PM

Of course as the transparency increases and the extinction decreases the airglow becomes a real problem.

 

My best night in the Kalahari (at 5200ft) was -3c with zero humidity and yielded 22.05 on the SQM at 03:30 when the galaxy set. Earlier in the evening when the galaxy was culminating the airglow was obscuring over 100 degrees of lateral horizon south/southeast and well over 30 degrees of altitude.

 

 

A shot from that night illustrating it :

 

Southern-Pole.png

 

 

You can clearly see the airglow as high as the SMC.

Where I live I would be happy to see the airglow - you will not find me complaining : )



#30 ChristopherBeere

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Posted 23 August 2019 - 02:36 PM

Where I live I would be happy to see the airglow - you will not find me complaining : )

 

Haha yeah at first i was really excited by it "What the heck is that ??"

 

Then you have to deal with it in your exposures and its a real PITA.



#31 BGazing

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Posted 23 August 2019 - 03:45 PM

 

That's what I get for preparing for a session with a nice chart...  Preparation is the kiss of death to getting a clear night or good seeing.  

lol.gif

so true



#32 Asbytec

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Posted 26 August 2019 - 09:17 AM

 

And I remember standing at an overlook at the Capitol Reef National Park.  There was sign that said:  "The average summer visibility from this point is 150 miles."

 

A few thoughts and questions:

 

What is your gut feeling about the typical transparency in your area?

 

What do you thinking are good indications of high transparency?

 

Jon

Yea, blueness of the sky is my primary indicator. Our transparency varies quite a bit in the tropics, humid air mass and particulates. I sometimes check the particulates in the area, and without fail when the count is high the transparency is very low. Fortunately, there are few mountains to constrain the air from blowing them off, and sometimes it does. Up north we lived right up against the coastal mountain range. When you drive up into the mountains and look back, it's a ghastly sight to see all the muck you have to observe through. Problem is, the mountains are usually plagued with uplift and fog as the humid air cools with altitude. Even up as high as 7,000 feet. 

 

I often check the water vapor charts, too, hoping that "dark" area will pass over head. Sometimes it does, and when it does deep sky is amazing. I was having an exceptional night one evening, when I pulled away from the eyepiece and looked up I was stunned to see the winter Milky Way like never before. I could trace it over most of the sky, most nights I can hardly see it in my yellow/orange zone at the edge of town. That was a night of exceptional seeing, too. Talk about rare nights when everything works. But, often enough the skies here (moved to a green zone) are dark enough and transparency is good enough to get some meaningful observing in. Sometimes not. But, yea, blue skies usually mean it's gonna be good. 

 

I tend to think seeing is important, too. DSOs are not simply faint splotches, they sometimes have more condensed star like detail that benefit form better seeing. When observing the Antennae one evening, I was able to spot two HII regions (?) near where the core of each galaxy might have been. They reminded me of E and F Trap. Speaking of E and F Trap, normally they wane in and out of view in my modest aperture. But the rare stunning night mentioned above, oh yea...maybe the first time I ever saw both of them as unwavering tiny pin points. Tiny bright specks. Seeing and transparency made a huge difference. The thankfulness I felt was memorable. Cuz, I still remember it. smile.gif

 

But, 150 miles! Yeeeow! I use the standard airport visibility forecast and observations. I've never seen 150 miles reported. (sigh) Maybe because it's mostly flat terrain. But, with 150 miles visibility you could see straight into low Earth orbit. lol.gif


Edited by Asbytec, 26 August 2019 - 09:20 AM.


#33 Starman1

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Posted 26 August 2019 - 09:56 AM

Transparency varies, I try to remind myself.

 

Here in LA, as light-polluted as it is, we occasionally have ultra-transparent nights where the city lights don't cause the atmosphere to glow much.

On such nights, I've seen stars to magnitude 5 with the naked eye.

But, we get more nights where the transparency is so low that Polaris becomes an averted vision star, and Jupiter is faint until it reaches about 15° above the horizon.

On the transparent night, the sky is a silver-grey.

On the non-transparent night the sky is a light blue with strong orange overtones, or yellow fading to orange.

Now that LA is moving to LED lighting, the light blue skies are becoming common.

 

And then, as has been pointed out many times, for about 4 to 5 months a year we get covered by low clouds and fog known as "the marine layer", where even the Moon can't shine through.

 

It's no wonder, then, that I travel to a dark site 100 miles away once a month to see the stars.  Unfortunately, that site is clouded out about 4 months a year.

So I travel 200 miles to get to another site, IF it isn't also clouded out.

I thought living in the west was supposed to be an astronomer's paradise. lol.gif



#34 Pcbessa

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Posted 26 August 2019 - 09:59 AM

Crazy Panda, what a report!

 

I am particularly delighted by reading it!

 

M81's brightest star cloud was obvious, though I could not quite see a well defined spiral structure due to the low altitude it was at at the time of observation.

 

 

Which star cloud is it? To which side of the galaxy? I think I remember seeing one of them too once in a Bortle 2 location.



#35 Jeff Morgan

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Posted 26 August 2019 - 11:53 AM

But, 150 miles! Yeeeow! I use the standard airport visibility forecast and observations. I've never seen 150 miles reported. (sigh) Maybe because it's mostly flat terrain. But, with 150 miles visibility you could see straight into low Earth orbit. lol.gif

 

You probably never will. Most aviation reporting station reports now stop at 10SM (statute miles). So, 10 = 10. And 150 = 10.

 

For an example of how this works you can call my local automated station: +1 928-717-1287

 

(Or you can go to many weather websites and look for "METAR" or "TAF" by desired airport.)

 

At this moment (10SM reported) I have no difficulty seeing Mt. Humphries at just over 60 nautical miles.

 

Aviation reporting stations (most of which are automated) were never designed for science. They were designed (and placed) to support aviation. Accuracy is just good enough for aviation purposes. Calibration can drift quite a bit before the station reports itself as needing maintenance.


Edited by Jeff Morgan, 26 August 2019 - 11:56 AM.

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#36 Arcticpaddler

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Posted 26 August 2019 - 04:43 PM

Excellent transparency is not limited to the West.  From Moose Mountain (1000' above Lake Superior) here in NE Minnesota, I can see the Porcupine Mtns in Michigan 75 miles away on a clear day.  The limiting factor here is often the curvature of the Earth...

 

I do remember driving back from Oregon, years ago, and seeing the glaciated peak of Mount Hood 130 miles away across the high desert of eastern Oregon.  Pretty cool.


Edited by Arcticpaddler, 26 August 2019 - 04:45 PM.


#37 Pcbessa

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Posted 27 August 2019 - 05:35 PM

Transparency is king!

 

Even in small cities with some only moderate levels of light pollution, transparency can give you a beautiful dark sky or a terrible night if haze is around.

 

This is of course critical for most DSOs.

 

I think excellent or good transparency requires:

- clean atmosphere (from dust, haze, water vapor, pollution), this can be done for example by a cold front and cold north winds clearing up the sky. Winds helps with transparency but it can reduce seeing.

- dry weather or climate is king. Desert skies are often fantastic, unless smoke or dust lifts, or high clouds form. That deep blue sky during day signals a good night. That's also why the tropics do not have the best skies due to moisture.

- altitude helps a lot 

- cold temperatures also help a lot

 

 

My best sky ever was in Iceland inland, Bortle 1, generally in winter time, with cold dry weather (sometimes windy too). I used to be able to see 200km in straight line in certain winter days there (beyond the curvature of the planet because of inversion). Now I live in Scotland, excellent transparency occurs but not so frequently. If I see the mountains 50km away in a clear way, I am lucky!

 

I also judge transparency by 1) blueness during daylight, 2) extent and detail of the Milky Way by naked eye, 3) spiral arms of certain galaxies such as M81, or overall brightness/detail seen in M33 


Edited by Pcbessa, 27 August 2019 - 05:39 PM.


#38 Jeff Morgan

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Posted 27 August 2019 - 06:58 PM

Excellent transparency is not limited to the West.  From Moose Mountain (1000' above Lake Superior) here in NE Minnesota, I can see the Porcupine Mtns in Michigan 75 miles away on a clear day.  The limiting factor here is often the curvature of the Earth...

 

I do remember driving back from Oregon, years ago, and seeing the glaciated peak of Mount Hood 130 miles away across the high desert of eastern Oregon.  Pretty cool.

 

Indeed, when I was on Green Turtle Cay in Abaco I was amazed at the sky conditions.

 

Since it was a scuba trip the only astronomy provision I packed was 7 x 50 binoculars. I would love to get back there with a telescope some day.



#39 pyrasanth

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Posted 02 September 2019 - 05:55 AM

This is a really interesting topic & very relevant to what happened last night.

 

The seeing was superb and I thought it was going to be a good night of imaging.

 

I started imaging the Cocoon nebula with a 3.5 nm Hydrogen Alpha filter on a C14 at F7.7. A 15 minute exposure revealed nothing more than a smudge and the OIII & S2 filters showed nothing other than stars. Looking more closely at the guider frame which is from the ONAG imaging in NIR the star showed a mush all around the periphery.

 

I guess I hit a night of great seeing-the guide star was barely moving- but the images were none existent.



#40 CrazyPanda

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Posted 06 October 2019 - 02:46 AM

Had the best transparency I've ever had from my backyard location this morning. Mag 6.3 stars were visible, I counted 11 stars in M45, saw quite a bit more of its nebulosity than I normally do, M33 was readily visible to the naked eye, the dust lanes in M31 had texture and detail to them, and I could trace the Great Rift all the way through Auriga. I've never seen so many dark lanes and such a broad extent of the autumn/winter Milky Way as I did tonight. I only wish the Moon hadn't been around for the first half of the evening so I could have seen the Cygnus region of the Milky Way in all its glory.

 

I could see the faintest hint of the dark region where the Horsehead nebula was without the use of a filter using my 25mm Zeiss E-PL and 15" F/4.5 dob. Adding a UHC filter made it obvious, though the shape of the horsehead wasn't very distinct (will need an H-Beta for that I think). The Flame Nebula was astronishingly contrasty, and the full M42 loop was obvious even without a filter. Lots of extended nebulosity visible in M42 without any filters. Adding my new OIII to the 35 Pan, or UHC to the 17 ES92 showed more in M42 than I've ever seen.

 

So far this has been a great year for observing!



#41 Pcbessa

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Posted 06 October 2019 - 10:14 AM

Had the best transparency I've ever had from my backyard location this morning. Mag 6.3 stars were visible, I counted 11 stars in M45, saw quite a bit more of its nebulosity than I normally do, M33 was readily visible to the naked eye, the dust lanes in M31 had texture and detail to them, and I could trace the Great Rift all the way through Auriga. I've never seen so many dark lanes and such a broad extent of the autumn/winter Milky Way as I did tonight. I only wish the Moon hadn't been around for the first half of the evening so I could have seen the Cygnus region of the Milky Way in all its glory.

 

I could see the faintest hint of the dark region where the Horsehead nebula was without the use of a filter using my 25mm Zeiss E-PL and 15" F/4.5 dob. Adding a UHC filter made it obvious, though the shape of the horsehead wasn't very distinct (will need an H-Beta for that I think). The Flame Nebula was astronishingly contrasty, and the full M42 loop was obvious even without a filter. Lots of extended nebulosity visible in M42 without any filters. Adding my new OIII to the 35 Pan, or UHC to the 17 ES92 showed more in M42 than I've ever seen.

 

So far this has been a great year for observing!

Where are you located? How dark is your sky? Bortle 1?

And what happened weather-wise to result in such a high transparency sky?

"Great rift through Auriga": that's amazing.

 

I had amazing nights here as well, as the sky is often very clean and dark, after the passage of rain and wind. It's Bortle 4, so I can see a few dust lanes in M31 on a good night, but not with much texture. But my scope is a 10" Dob.



#42 CrazyPanda

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Posted 06 October 2019 - 07:47 PM

Where are you located? How dark is your sky? Bortle 1?

And what happened weather-wise to result in such a high transparency sky?

"Great rift through Auriga": that's amazing.

 

I had amazing nights here as well, as the sky is often very clean and dark, after the passage of rain and wind. It's Bortle 4, so I can see a few dust lanes in M31 on a good night, but not with much texture. But my scope is a 10" Dob.

Sky is only bortle 4, maybe SQM 21.2-21.4 or something along those lines.

Weather-wise, this time of year historically has less humidity, though climate change has changed that over the last 25 years. Clear, dark blue skies and short plane vapor trails were the norm, now they're rare. Last night/this morning had deep blue skies and short vapor trails again. High winds I think helped.


Edited by CrazyPanda, 06 October 2019 - 07:48 PM.


#43 Spartinix

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Posted 07 October 2019 - 03:19 PM

I'm pretty happy where I live too now. I can also see the great rift stretch far into Auriga. I love lying on my back and trace the dark clouds from Cygnus almost up to the Pole star and from in between Cygnus and Cassiopeia to Auriga crossing the Milky Way to Taurus. The fine lanes near Perseus and near Deneb are awesome too.

Edited by Spartinix, 07 October 2019 - 03:21 PM.

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#44 Astro-Master

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Posted 09 October 2019 - 09:22 PM

I have noticed that busy highways like Interstate 15 near Lone Pine that are in a valley with high mountains on both sides and Interstate 5, in the San Joaquin Valley, and Interstate 10 near San Bernardino get a lot of pollution that kills the transparency. 

 

I stopped by Mt. Pinos on the way back from a trip to Kings Canyon and was disappointed, the pollution from the San Joaquin Valley had crept up the mountain, the skies were not very transparent even at 8,300 ft.

 

Find a high mountain far away from busy highways, and you have a better chance for good transparency like Great Basin National Park.

.


Edited by Astro-Master, 09 October 2019 - 09:23 PM.



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