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Why is when my seeing excellent, transparency is garbage?

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#1 skycamper

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Posted 21 March 2023 - 02:36 PM

Is this just a coincidence that Im hallucinating?  I tried looking up this relationship but got no where.  Is this a thing or not?


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#2 kathyastro

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Posted 21 March 2023 - 02:39 PM

Murphy's Law.

 

And when the seeing and transparency are both good, it's a full Moon. lol.gif


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#3 matt_astro_tx

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Posted 21 March 2023 - 02:40 PM

I see this quite often too.  Like Kathy said, it just be like that sometimes.



#4 Phillip Creed

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Posted 21 March 2023 - 02:45 PM

Steady skies are usually caused by stagnant air masses with very little air movement.  Perfect recipe for trapping pollutants that reduces transparency.

Clear(er) Skies,

Phil


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#5 Astrojensen

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Posted 21 March 2023 - 03:00 PM

It really depends on local conditions. My sites seem to be quite erratic, and nights with low transparency doesn't often have particularly good seeing, since fog is usually associated with temperature differences. On the contrary, I can often have very good seeing on windy nights, yet wind is also no guarantee for good seeing, and I've had completely clear, windless nights with amazing seeing. 

 

Wind bringing in warmer air in winter or spring = just horrible seeing. 

 

Fog forming on a cold, still spring night, after a warm day = horrible seeing, mixed with moments of absolute stillness. The early evening hours, just after sunset, before the fog forms, can be pure magic.

 

Dry wind from the North or East during winter or spring = amazing seeing possible, but not guaranteed. 

 

Hot, muggy summer night = usually has great seeing, especially in the morning hours. 

 

 

Clear skies!

Thomas, Denmark


Edited by Astrojensen, 21 March 2023 - 03:01 PM.

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#6 bobruben

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Posted 21 March 2023 - 03:03 PM

My best view of the planets was on a hot muggy, misty night in downstate Illinois.

 

Later, I set up an alarm on ClearDarkSkies to email me when skies were very transparent and very still. It went off like two times in a year.

 

It's curse, but I am very fond of breathing air.


Edited by bobruben, 21 March 2023 - 03:04 PM.

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#7 norvegicus

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Posted 21 March 2023 - 03:34 PM

Turbulent air (poor seeing) clears out the debris and haze (transparency).   So usually transparency is good when the seeing is poor.

 

Still air tends to be hazy.  Pilots like to see a hazy day because it means there is less turbulence. 

 

Occasionally there will just be less debris and haze and the air will also be still.


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#8 ram812

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Posted 21 March 2023 - 03:42 PM

Depends on the season in PNW😃. It's erratic behavior is absolutely unpredictable.RAM😁

Edited by ram812, 21 March 2023 - 03:45 PM.


#9 TOMDEY

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Posted 21 March 2023 - 04:28 PM

The most spectacular seeing I have ever experienced was an unusual night that was so ~muggy~ that I almost didn't even bother to open the dome and fire up the trusty 17.5-incher (that sports unusually good optics). But I gave a gander and aimed at Jupiter --- exquisite detail that I haven't seen before or since. And that was many decades ago. That modest scope was strangely fabulous for comfort, contrast, and resolution. Great mirror(s), excellent support of the PM and SM (whiffle), great stable alignment and --- true tube lined with sheet cork and black velvet. I think those conspired to produce good imagery... so that spectacular nights allowed the full chain to perform as imagined.   Tom


Edited by TOMDEY, 21 March 2023 - 08:11 PM.

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#10 Keith Rivich

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Posted 21 March 2023 - 06:59 PM

Is this just a coincidence that Im hallucinating?  I tried looking up this relationship but got no where.  Is this a thing or not?

We live with this all the time here on the Gulf Coast. In the middle the summer I can look at Jupiter at 700+ power just about anytime. Transparency, though, stinks. However, if one is willing to wait until 2:00am or so, something magical happens: The surface humidity peaks (everything is soaking wet) and the transparency can become quite good. 

 

I posted in another thread that at certain times of the year the humidity can be fairly low and the seeing can be quite good. The winter cold fronts pass north of us and the Gulf of Mexico is still cool enough to retain its moisture. Its when the Bermuda High settles in when our transparency goes south. 


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#11 maroubra_boy

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Posted 21 March 2023 - 08:02 PM

Skycamper,

By your avatar I see you are in Beaverton OR. If you are observing within the boundaries of Portland then I can see why you are in such a world of bother. As others have said, it is due to your site's location. If you are observing from Beaverton/Portland it is in a valley surrounded by mountains, you will need to look for a different location to improve things for yourself.

It all comes down to site selection, and this takes time to find a site that provides conditions that are good for astro, meaning routinely stable seeing & transparency. Just using a site because it is dark is not good enough as a feasibility study. It needs to be far more considered and time has to be spent scouting out locations with an eye open for the weather patterns and what these bring with them in terms of what I call "astro conditions". And if you are observing from home you have next to no choice but to work with what you are given, which doesn't mean just blindly setting up your scope, instead paying attention to conditions on the night and then shape your viewing around the conditions that are presented**. This adaptation needs to be made not just at home but when you do go bush, or you are just setting yourself up for a crap fight of frustration.

I don't know where you are doing your observing - it would be a big help if you did say so. But if you are prepared to look for a better astro location, here's a couple of tips - but to clarify I need to explain something first on where I am coming from: My observing buddies and I spent several years looking for a good astro site and in the end we worked out key weather patterns of where WE are and that these are unique to THIS wider area, what we found was understanding the conditions that made for a good site allowed us to then locate a site with the micro-climate that made for excellent astro conditions while the wider area around us was crap. So the following is to give you an idea of what to look for, NOT "you must look for exactly this" because that is just dumb because the Blue Mountains west of Sydney are not the same thing as the mountains that surround Portland - I looked up a topographic map of Portland and its surrounding terrain. So while our locations are significantly different, there are some things that will remain key in helping you find the best astro location possible.

* Don't set up in valleys/basins. Dew, fog & pollution settles in these meaning reduced transparency. The ridge tops is where you want to be.
* Look for areas where people are doing hang gliding and paragliding. These will be along ridge tops and you may find that a night there will be laminar airflow coming off from the ridge tops and cascading down into the valley below, or even blowing up over the ridge top close to the ledge. There is a direct correlation between those locations where paragliders set off from during the day to a site that at night is outstanding for astro. Mt Blackheath lookout in the Blue Mountains is one such place.
* Ask at rural airfields for info on weather patterns as pilots PREFER to fly in the same conditions that WE as astronomers favour - little atmospheric turbulence and good transparency. Everyone prefers a smooth flight and having a clear sky... These airfields are a font of information and can help with identifying good sites - they will know where the dominant locations of laminar airflow will be, along with the paragliders.
* Stay away from agricultural land. This sort of land is more lush and irrigated meaning dew at night and the associated reduced transparency that comes with it. Coincidentally this is also more often than not in valleys too...
* Look to understand the wider seasonal weather patterns of where you are. Where the dominant winds are during different seasons, how the day's heat affects wind direction and what these mean for moisture content in the air mass, such as a coastal wind will bring higher moisture content with it and as it comes over a mountain range it turns to cloud, and things might change when you head to the mountains to the east of Portland - You need to work these out.

And good astro conditions can be entirely seasonal between different locations.

Mountains can also mean poorer seeing than stable seeing, as this is all affected by the geography and weather systems of the location. For example, in the Blue Mountains excellent seeing and transparency can be found on the clear sandstone ridgetops, particularly in winter when the dominant wind is from the west. During summer, the dominant wind is often from the east as the heat of the Sydney basin pulls in moist air from the Pacific Ocean, and as this wind reaches the Blue Mountains it turns to cloud and if it is clear transparency will be down because of the higher moisture content and heat. And often when there is a strong easterly wind blowing, the 'Mountains will be clouded out but the Sydney basin sky will be crystal clear... you need to come to understand the conditions for where you live, not just for wider Portland but include the mountains all around it. Unless you do the hard work of visiting and working out different sites around you, you just won't find a site that will give you the best astro conditions for you. And you may need to have two or more locations depending on the season and weather of the day.

Like I said, my friends and I spent years looking for a good, safe site to do our astro thing at. We came to understand the local weather patterns, geographic and environmental conditions that mean a good site for astro. We also understand that we had to have alternate sites up our sleeve if our preferred dark site was clouded out, even if the quality of the sky isn't the finest it can mean doing some astro or not. And we continue looking, exploring and learning. The geographic and environmental conditions that provide for excellent astro conditions for us also means that these unique locations hardly ever experience any dew! In the 16 years we have been using this site we had dew form only 7 times, and of these only twice was this dew significant enough to affect our scopes. So much so that knowing what we know as a club about site selection and how this also means dew and astro are not inseparable bedfellows, we as individuals won't go to other locations because they are known as dew traps with poor transparency. I won't knowingly subject my gear to dew if I know that dew can be avoided and have better astro conditions and a better time.

There are clear benefits to taking the time to find those sites that do provide the best conditions for astro for where you are. Just finding an open grassy field is just not good enough your only search parameters.

Alex.

** When at home, spend a few minutes just looking up at the night sky and figure out what it is giving as conditions. A lot of twinkle in the stars means poor seeing. What naked eye DSO's you can see relates directly to the quality of transparency. You then adapt your session to what this information tells you. This you should also do at a dark site - no use wasting time chasing faint fuzzy galaxies if you know that transparency is down... you may see the core and a fuzzy mass, but no detail and an underwhelming view.

Alex.

Edited by maroubra_boy, 22 March 2023 - 02:18 PM.

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#12 UnityLover

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Posted 21 March 2023 - 08:16 PM

Its the site, my site often has average to above average transparency, but seeing is almost always horrible.



#13 csrlice12

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Posted 22 March 2023 - 10:06 AM

Because having both at the same time isn't safe for someone alone in the dark in the middle of nowhere.wink.gif

 

Ok, semiwink.gif



#14 MikiBee

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Posted 22 March 2023 - 11:35 AM

Proximity to the ocean plus the mountains will work against you (and many of us). I often check the ClearDarkSky forecast and I would say I would see the perfect transparency and perfect seeing on the same hour maybe 2-3 times a year.

 

What can happen often is that on nights with great transparency and just average (3/5) seeing you get from time time these moments of perfect seeing, you find a pocket of calm air usually only in one narrow direction in the sky, 3.5 minutes later and its gone. 



#15 Alan D. Whitman

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Posted 22 March 2023 - 01:02 PM

Steady skies are usually caused by stagnant air masses with very little air movement.  Perfect recipe for trapping pollutants that reduces transparency.

As a retired meteorologist I can say that Phillip Creed is correct, as is Norvegicus who made similar points. And Maroubra Boy knows what he is talking about.

 

All I will add is that there are some places (like here where I chose to retire primarily because of its suitability for astronomy) where seeing is the only real variable because transparency is rarely less than excellent on a clear night. I have NEVER had fog here on a clear night in this semi-arid valley in 27 years. Fog occurs perhaps four winter days, and it only forms over melting snow, and the sky is overcast in those conditions anyways. The closest significant upstream pollution sources are in Asia (and in the last decade I have noticed that once in a long while the Pacific Ocean will fail to entirely wash the air polluted by China's coal plants and other heavy industry before it gets here).

 

We do have forest fire smoke sometimes in summer. And we do, this particular week, have some dust in the air because of spring street-sweeping. And if we have an old high pressure area, transparency will eventually fall off to just very good after several days because of the small minority who heat with wood or orchardists burning slash. But on the great majority of clear nights transparency is excellent here, which is why I retired here. When I drive north to the Okanagan Valley's population centre, Kelowna, I can usually see the smog sitting low over that city from all the normal urban sources when it first comes into sight in the distance.


Edited by Alan D. Whitman, 22 March 2023 - 01:13 PM.

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#16 Tony Flanders

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Posted 22 March 2023 - 08:34 PM

It's really dangerous to generalize. Our best transparency in the northeastern U.S. is usually when there's a cold wind from the northwest, typically accompanied by poor seeing. But all four combinations -- and gradations thereof -- are perfectly possible. Every now and then we get nights with great transparency and great seeing. And it's certainly common enough to have terrible transparency together with terrible seeing.

 

Most of the world's major observatories are located in places where both the transparency and seeing are routinely good to excellent.


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#17 maroubra_boy

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Posted 22 March 2023 - 09:10 PM

No one is generalising here. Quite on the contrary, the last few posts have been anything but encouraging to do the necessary legwork to find the best location from themself. As you said, the trick is to find a location with routinely good seeing & transparency, something that needs time to be found. Like I said, finding an open paddock at a dark location is not going to cut it as a suitable site parameter or feasibility study. It asked time & keeping one's eyes open to multiple factors. Along with the prospect of needing more than one site according to the seasons.

#18 daveb2022

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Posted 23 March 2023 - 10:00 AM

I live in a large valley and find my location provides better than average seeing and transparency more often than not, provided clouds aren't effecting things.Even though textbook perfect evenings are rare, so are the very poor conditions. The seeing changes much more than transparency and while both can change throughout the night, the transparency usually stays at the same level while seeing often changes as the night moves on. I can go for a week and the transparency is almost the same night after night as opposed to the seeing which can be all over the place.  Fog can be an issue in the winter and a clear night can go from good seeing to obscured in a short time, especially prior to dawn. I feel fortunate that last fall and winter only produced a couple of nights that forced me back inside before knowing what the conditions were or have the seeing/transparency conditions degrade enough to make me give up. Many DSOs are often less effected by poor seeing than planets, so on poor to mediocre nights of seeing, I'll spend less time on planets/moon. From my backyard, poor transparency can be like putting on a ND filter and hits DSO's harder. The other night the skies looked clear but the stars were so dim in binos that I didn't consider setting up. Light pollution is another factor and I suspect can be a factor with transparency, but overall, if the clouds don't appear, I feel I have pretty good skies on average from the big bowl I live in.   


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#19 skycamper

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Posted 28 March 2023 - 10:11 PM

Been thinking about my post here, also took a long read of Maroubra Boy stated and what others have offered.   My observatory is in a dome in my backyard which is fairly shielded from streetlights with moderate housing density.  Here is a photo of a typical night im seeing.  I dont know much about seeing and transparency since imaging time is at a premium.  With a job, house, kids, wife, aging parents and even grandparents, its hard to find the time. When i do im already exhausted.   Packing up and going to better skies is just not something I can do.  That said, I really got into dual imaging to double my exposure time to make up for this.

 

Clear skies do happen here more often than you think but sometimes weeks or months go by without significant clearing.  

 

Here is my immediate area and some typical guiding I see with an OAG at 800mm.

 

Another thing I think about is using PI weighted batch pre-processing,  if im imaging any clear night in which I typically take advantage of I just let the cameras bang away until I have an image. I dont throw out any subs unless they are really awful.  I dont blink through all of them.  

 

I would say in my current location of 12 yrs ive never gone outside and said, "OMG the stars arnt twinkling!!"   Time to image!    I just do it and hope for the best.  Unless Im being lazy which is harder to do these days if im set up in the observatory and its ready to go. 

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Edited by skycamper, 28 March 2023 - 10:17 PM.


#20 skycamper

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Posted 28 March 2023 - 10:23 PM

I would say this is a typical sub exposure I would see on a night of Avg seeing 30" exp at 800mm on a AP1200.  Or its just wishful thinking!   I think Im trying hard to at least be seeing limited and not add to my problems.  Except for the old 12" newt I mounted the other day.  Trying to work the bugs out of that.   

 

If I ever move from here it will be to a dark sky with seeing and transparency that are at least better than where im at.   I'm thinking somewhere near Goldendale WA near their observatory.  And no income tax on my retirement. Lol

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#21 maroubra_boy

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Posted 29 March 2023 - 04:00 PM

I very much understand the situation you are in. If trying to do this solo, yeah, going exploring needs a lot of free time. We did our research collectively but our situation was unique in this way. 99% of my astro is done from my home in Sydney & only when I can pinch the time on the spare of the moment. Oh, I very much get your situation.

There are two routes to explore here. The first looks after your immediate situation in helping out with your current imaging. For this you might like to pose a question for help in the imaging fora for assistance with dicky seeing. The other is by starting remote exploration of sites using the net.

The first option you know what to do.

The second one, you can start by finding the smaller airfields say within a 3hr drive limit & email them. Same with paragliding clubs. As I mentioned earlier, the conditions pilots like to fly in are the same as we any to observe under. This will if nothing else start helping you form a picture of the seasonal weather patterns around the different locations. Paragliding sites in particular are VERY seasonal. If it snows in winter then no paragliding, but the airfields will still have the local knowledge.

Look for patterns of geography with what gives good seeing - good seeing means laminar air flow & smooth flying. Then you can start identifying possible sites on the ground using Google Maps.

What I getting at is looking for a good astro site doesn't need to be a random exercise. You can start it of from in front of your computer. For my Club now, armed with the knowledge we have gained when we look for new or alternate sites our search is far more refined. We know what locations to avoid & who to ask.

If you have a mate or observing buddy this can be a big asset in your quest.

All of this isn't to replace your home situation. It is to find a site away from home that does offer better astro conditions for when you can get away, just like for me & my Clubmates.

Alex.
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#22 Cpk133

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Posted 04 April 2023 - 02:23 PM

Considering your immobility, the best you can do is make the most of local seeing conditions.  By that I mean open things up early and try to get things thermally stable.  Pay attention to weather patters that are conducive to good seeing in your locale, you might even keep a journal since you have actual data.  You may not blow off a clear night for poor seeing, but if the seeing forecast is really good, you might want to make sure you’re ready to go.  You probably cant just pick up and move your obsy, but try to pick targets that aren't over nearby rooftops or other sources of heat.  Even your on breath / body heat can affect seeing, so if you’re using a small slit opening observatory, maybe you can find ways to minimize nearby heat.   I can usually pick out nights with excellent seeing prospects many days in advance by watching the jetstream, surface winds and local forecast. 


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#23 Cpk133

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Posted 04 April 2023 - 02:35 PM

Been thinking about my post here, also took a long read of Maroubra Boy stated and what others have offered.   My observatory is in a dome in my backyard which is fairly shielded from streetlights with moderate housing density.  Here is a photo of a typical night im seeing.  I dont know much about seeing and transparency since imaging time is at a premium.  With a job, house, kids, wife, aging parents and even grandparents, its hard to find the time. When i do im already exhausted.   Packing up and going to better skies is just not something I can do.  That said, I really got into dual imaging to double my exposure time to make up for this.

 

Clear skies do happen here more often than you think but sometimes weeks or months go by without significant clearing.  

 

Here is my immediate area and some typical guiding I see with an OAG at 800mm.

 

Another thing I think about is using PI weighted batch pre-processing,  if im imaging any clear night in which I typically take advantage of I just let the cameras bang away until I have an image. I dont throw out any subs unless they are really awful.  I dont blink through all of them.  

 

I would say in my current location of 12 yrs ive never gone outside and said, "OMG the stars arnt twinkling!!"   Time to image!    I just do it and hope for the best.  Unless Im being lazy which is harder to do these days if im set up in the observatory and its ready to go. 

Cant expect good seeing with this kind of jetstream (1-30-23) from your screen shot:

Jetstream1-30.png

earth.nullschool.net


Edited by Cpk133, 04 April 2023 - 02:37 PM.



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