Can good seeing be predicted?

[ballaratdragons (Ken)]

Interesting point Paul!

Less heat haze in the bush too!

[Starkler (Geoff)]

Keep it on topic please !

[[1ponders] (Paul)]

But in the bush you have to put up the the volatile oils released by eucalyps that cloud transparency, ie the "Blue Mountains"

[ballaratdragons (Ken)]

Originally Posted by Starkler

Keep it on topic please !

??? It is Geoff! These all have a bearing on seeing. Especially predicting the seeing at differing environments.

Originally Posted by plunderpants

volatile oils released by eucalyps that cloud transparency, ie the "Blue Mountains"

Never heard of that one Paul! I've never seen it here. Can it be seen?

[fringe_dweller]

to add to that Paul - i was reading the other day that particle pollution such as created by industry and cars ect. in the cities - has the ability to retain heat from the day further effecting seeing in built up areas

[[1ponders] (Paul)]

When I first moved to the coast here when I was 13 and just newly interested in astronomy the skies were unbelievable. clear and often steady from what I can remember. Now I live about 25 km away and I'm yet to see a night this year that I would call really memorable. The exception would have been Duckadang that is about 70km inland from here, well away from the coastal fringe. It may have been the fantastic tranparency that night that blew me away, but I'm pretty sure the seing was more than above average from my recent experinces here on the coast

[rochler]

but I can confidently predict that the 'seeing' next year will be worse than this year. At least for me anyhow - AGL just decided to put up some giant Stobie poles along my back fence. Not the normal ones mind. but the huge 60' ones. Totally stuffs up the whole western sky up to about 60 degrees. Meanwhile, all the neighbours are installing floodlights, garden lights, christmas blinkin' lights, etc.

Apart from that, my eyes will be getting older and so will my equipment...

[[1ponders] (Paul)]

I seem to recall in an article or on a program on global dimming a couple of months ago the fine chemical aerosols and particulates are forming a identifiable blanket in the atmosphere about 15 to 20 km up (I think that's the distance) and that new differential thermal layers may develop on either side of this layer. Has anyone heard of this or can enlighten me further about this problem?

[ballaratdragons (Ken)]

It still sounds like predicting the seeing for any given night is still up to "I'll stick the scope out and have a look". There appears to be to many variants to consider. Wind has a great way of blowing muck away but too much wind ruins seeing anyway!(usually).

So to answer your original question Geoff: 'I don't know'.

[[1ponders] (Paul)]

"Very often we are our own worst enemy as we foolishly build stumbling blocks on the path that leads to success and happiness."
Louis Binstock

[rumples riot]

My experience is this. Nights of great seeing typically precede a cold front moving in from the West. The warm air rises up over the top of the cold front. Seeing is especially good when the night is still and a little humid during late summer. All my best imaging efforts this year have been late summer on still humid nights just before cold front passes.

Local topography also influences seeing. If you are in zone like I am just behind a hills range with the prevailing wind rushing up onto those hills, the seeing will be less than perfect most of the year, too much turbulence. Only on nights when the wind is going the other direction will the seeing be at least average.

Good studies to read are those by damien peach. Worth looking at. They helped me predict nights of good seeing with some certainty. The image that Davo submitted shows my point very well. That huge cloud bank was a cold front moving through underneath a High that was centred over Tassie.

Anyway, that's about good as it gets for me. Should have done meteorology at Uni instead.

Paul

[Starkler (Geoff)]

Thanks Paul, this is the sort of info thats useful

[Robert_T]

Hi Guys, following this thread with considerable interest, reliable prediction of good seeing conditions would be the holy grail of planetary observers... then again if I knew it might tell me I'm wasting my time imaging from my brissy backyard - ignorance is bliss. Surrounded by tile roofed town houses I've often wondered how much (at least early evening) my poor seeing had to do with the more micro-level conditions here, but I'll be keeping an eye more to those isobars from now on.

It occurs that one of the biggest barriers to predicting seeing is the lack of an easy mechanism to measure it and to measure it consistently between observers. I often suspect that what one observer might rate as 6/10 seeing would be rated differently by others; terms such as "average", "good" etc are quite subjective and might reflect considerable differences in actual seeing conditions.

I wondered whether in the Webcam revolution whether a tool might be developed to objectively measure seeing much like photometers measure stellar magnitude - excuse my ignorance if this already exists. For example, by producing a measure of the range of deformation of any outline or object selected over a series of avi frames. If this could be easily done (some on you IT gurus) then there could be a multitude of consistent seeing measurements taken across the country that could be recorded and linked to the meteorology and from this perhaps a better means of predicting seeing might some

cheers,

[slice of heaven]

Originally Posted by fringe_dweller

your right Ken, tho have seen nights with good seeing but really windy - or cloudy - you have to laugh on those occasions eh
traditionally it is widely followed that when the isobars are widely spaced enough in an isobaric chart - most commonly with sloooow moving huge high pressure systems - that is the time - but the trailing western edge can be dodgy with an approaching front ect. influencing ahead of itself - but on rare occasions here it can be good with huge spaced slooooow lows too -
i agree about seeing for the last couple of years with these antarctic lows reaching up in to southern oz all thru summer - they used to get held down by the dominant, ants pace, highs - but the little puny wishy washy, tightly spaced, highs we have been getting for a few yeras are taking a belting at the hands of these roaring 40's type lows - they get pushed and bullied along and out of the way before they can get established - i remember a few huge high pressure sytems hanging around for what seemed weeks years ago?

That sums it up for me too,Kearn

[iceman (Mike)]

DaveP I removed the inline link to the image, it was over 300k! Please check the size before using the IMG tags, or have a link to it with a hint to its size, so people can make a choice about whether to download it.

On topic, I've only had 1-2 nights of what i'd call *great* seeing all year, and of course this year I've been noticing thanks to webcam imaging. Of course I haven't been out all night every night, and so I may have missed some.

I have noticed though that early mornings are generally much better than evenings, possibly due to scope cooling down over night, possibly due to lack of turbulence in the air and the steady temperatures at that time of morning.

I'm sure Bird will have some insight.

But Geoff is right, lack of jetstream doesn't guarantee good seeing, but presence of jet stream almost always guarantees bad seeing.

[bird (Anthony Wesley)]

I've had a lot of shocking seeing this year, even on nights when I would have sworn it was going to be fabulous. Part of the cause will be your local environment - if you're in an urban area like me then you can pretty much forget about good seeing until the wee small hours when all the bricks and ashphalt around have cooled down.

From what I can tell so far, the best seeing comes about when you have a dry, cloudless night. If there's moisture around then the seeing will not be very good. On the other hand, if there are clouds around then the ambient temp will be higher and it becomes easier to get the scope to thermal equilibrium so it can *seem* like the seeing is better when you can get a look between the clouds.

I've started watching the jetstream, so maybe over this summer I'll get a feeling for how the seeing correlates to that, it would make sense if low jetstream activity also made for better seeing.

regards, Bird

[slice of heaven]

Originally Posted by bird

If there's moisture around then the seeing will not be very good.

That's transparency, the other half of the equation. The moisture is the number 1 killer of early morning sessions for me locally. Seeing can be still great,but the transparency is shocking
Transparency is easier to predict.
3 things to check during the day for expected clear nights..
1)weather maps./No clouds No fronts moving in Stable highs/lows
2)The white haze around the sun. /The less white haze around the sun the drier the atmosphere.
3) Colour of the sunset / Pinks,reds and yellows make for a pretty picture but what you need is a deep blue sunset, absence of moisture in the atmosphere.

[rumples riot]

Yeah even dry air cannot reliably predict good seeing. It all depends on local conditions. For me dry air does not necessarily equate to good seeing, it can mean my neighbours roof is producing heat blooms, unstable currents behiind the hills face thereby increasing turbulence. Like I said locally here humid nights that are still and the wind blowing the other wayduring late summer equate to seeing above 6. Also usually have a period just after sunset for an hour or so when the seeing is good. Then it all goes to crap.

Slice I know what your saying about Murray Bridge. In the last 5 years I have had projects there at least once a year. Driving in at 7 am the view of the mist from the hill shows how bad transparency can be. Its because you have a water source right near the town. Heat coming off the town will produce condensation over the water which is cold. This spreads and so you get bad trasparency. Especially where you are.

[slice of heaven]

Originally Posted by rumples riot

It all depends on local conditions.

Definitely. Getting to know your local conditions pays off for sure, saves a lot of wasted effort.

[acropolite (Phil)]

Land breezes at night, sea breezes during the day, it's temperature differential that causes atmoshpheric turbulence, I suspect that's why the seeing in the tropics is reputed to be so good, no jetstream and relatively close atmospheric and ground temperatures.