Predicting Transparency (and Good Seeing Conditions)?

[Hayduke27]

I recently had one of my most memorable observing sessions to date (REPORT HERE).  The reason this session really stood out was due in very large part to having extremely good transparency AND seeing that morning.

Just a couple of days ago I had a clear morning and tried to repeat the experience.  I did have a nice session, but when I turned my scope back to the planets the transparency was dismal compared to my prior session.  I could barely make out any detail on the planets, and views were just not very impressive overall.

Now it is not news to me that we are observing through the atmosphere of Earth, and looking out through all that gas is just like looking through water-- it can be anything from mucky and turbulent to crystal-clear and still.  This all makes sense to me.  My question is this: Are there some conditions I can watch to predict when the transparency and seeing will be good on a given night?

Just off the top of my head I can deduce that any smoke or smog present would negatively affect viewing.  It also seems like windy conditions would have a detrimental effect (aside from the wobbling it physically causes the scope and equipment).  Also I can see how cold air is likely more transparent, as you have less "heat wave" effect.

What conditions make for excellent transparency and seeing conditions?  What a treat it was to have a clear AND transparent night, and now I want to be able to keep my eye out for more!!

[Demonperformer]

The only extra thing that springs to mind is to set up so you are not observing over large masses of concrete or buildings. These tend to absorb heat and disturb the air above them as they cool, a process which can go on for a very long period into the night (far longer than you might expect).

[niallk]

I'm not sure about predicting transparancy - other than looking at forecasts which break out high cloud / humidity; as for dust and smog - high pressure & no winds keeps pollutant particles in the air; sahara dust can be swept up from the south.

But for 'seeing' (the wobbly-ness or the 'heat wave' part you mention), I always check the jetstream forecast:

https://www.netweather.tv/charts-and-data/jetstream

Not looking across the roofs of houses is important, and can be helpful to be set up and surrounded by grass, as already mentioned above.  The scope needs to be well cooled.  If the conditions are looking good for high power planetary views, I cool my 15" chunk o' glass for 3hrs with a fan to get the best views... it's worth it 

The other issue is that the planets are at fairly low altitudes from Ireland/UK for the next couple of years: which is not thebest as one observes through significantly more low lying layers of the atmosphere.  However, it can still be well worth trying: I had my best ever views of Saturn and Jupiter last year while they were pretty low, observing south over the sea, no land.  I've read that some people try a coloured filter to eliminate some of the fluctuating atmospheric dispersion effects, but I havent tried it myself.  Interesting idea though!

[Stu]

Just to clarify terminology here. Transparency relates to how clear the sky is in terms of high haze, smog, pollution etc and largely affects your ability to see faint DSOs. Seeing is what describes the turbulence in the atmosphere which determines how objects appear at high magnification, particularly planets and doubles etc. It seems you had excellent seeing so the planetary views you got were stable at high power. This is determined by planetary altitude, jet stream position, local thermal effects eg has it been a hot day with the land and buildings creating convection currents. Lots of factors to consider. Often early hours ie when you were observing in your recent report, is best. As you found out!

[Paz]

I don't know if it is coincidence or causal but I have noted a number of very good sessions I have had that follow in the days after big storms have swept the country. 

[chiltonstar]

Before I start observing, I always do a quick seeing and transparency check. My garden is a rural location 'ish with a 20.8/NELM 6.2 value on a good night - I check the transparency quickly by looking for some stars I know to be mag 5.5 to 6 close to obvious stars, and check the seeing by looking initially at the visual appearance of say Sirius, then if that is good (not much scintillation), on to a convenient pair of double stars with a 1 to 2 arcsec separation to get a quantitative idea of seeing. It is rare to find good seeing and transparency together I find!

Chris

[Demonperformer]

28 minutes ago, Stu said:

Transparency relates to how clear the sky is in terms of high haze, smog, pollution etc and largely affects your ability to see faint DSOs. Seeing is what describes the turbulence in the atmosphere which determines how objects appear at high magnification, particularly planets and doubles etc.

Apologies if my earlier response confused the issue.

[knobby]

42 minutes ago, Demonperformer said:

Apologies if my earlier response confused the issue.

No confusion , just provoked clarification for people reading the thread, if no one asks, no one answers and no one learns.

[Pondus]

 

12 hours ago, Hayduke27 said:

What conditions make for excellent transparency?  What a treat it was to have a clear AND transparent night, and now I want to be able to keep my eye out for more!!

 

I`m not sure if this really answers Your question, but since you are US based why dont try out :

http://www.cleardarksky.com/csk/  

Pick out the chart-location  nearest to you, there must be 100+ in Colorado alone, and check if the transparency forecast is reliable?

 

Rune

[Hayduke27]

5 hours ago, Stu said:

Just to clarify terminology here. Transparency relates to how clear the sky is in terms of high haze, smog, pollution etc and largely affects your ability to see faint DSOs. Seeing is what describes the turbulence in the atmosphere which determines how objects appear at high magnification, particularly planets and doubles etc. It seems you had excellent seeing so the planetary views you got were stable at high power. This is determined by planetary altitude, jet stream position, local thermal effects eg has it been a hot day with the land and buildings creating convection currents. Lots of factors to consider. Often early hours ie when you were observing in your recent report, is best. As you found out!

Thanks for the clarification Stu!  I understand, and "seeing" is what I was referring to it seems.  There are no urban areas near me, so smog is not an issue, and there are no big fires ablaze at current time, so my transparency has been darn good.  It's the seeing that really got me on my recent notable session.  Good seeing has caught my imagination, I need more!!!

[Hayduke27]

1 hour ago, Pondus said:

 

 

I`m not sure if this really answers Your question, but since you are US based why dont try out :

http://www.cleardarksky.com/csk/  

Pick out the chart-location  nearest to you, there must be 100+ in Colorado alone, and check if the transparency forecast is reliable?

 

Rune

One of these sites is right in my hometown!  Great source of info, thanks for the link!!

[Nyctimene]

German amateurs (Sternwarte Laupheim; Hans-Jürgen Merk) are measuring the infrared radiation temperature with a simple infrared thermometer to gauge transparency. Space temperature is -270° C; within the atmosphere, the temperature increases due to the clouds emission of infrared radiation. H.-J. Merk gives these values: dense cloud cover +6°; partly cloudy -12°; hazy - 17°; clear, good transparency -20°, clear, very good conditions -24°. The second graph in the link to the Sternwarte Laupheim shows from left to right partly cloudy sky, clouded out sky and clear sky:

http://www.wetterwarte-sued.com/v_1_0/aktuelles/himmelstemperatur.php

No own experience with this way of transparency prediction and evaluation, but it seems to be a simple way (in combination with SQM-L measurements) to get some objective data of sky transparency and light pollution levels.

Edit: just found this - a DIY Peltier element cloud detector, based on the same principle:

https://www.noao.edu/staff/gillespie/projects/cloud-detector.html

Hth

Stephan

[Demonperformer]

Interesting idea.

[Stu]

4 hours ago, Hayduke27 said:

Good seeing has caught my imagination, I need more!!!

I think you’ll find there is a queue for that