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Old 13-02-2012, 06:08 PM
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coldlegs (Stephen)
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How do you pick your best seeing nights and avoid the worst??

How do you pick your best seeing nights and avoid the worst??

In astrophotography seeing is all important and picking the best nights can be almost as difficult as accurate fortune telling. Some say predicting the weather is pretty close to fortune telling so I'm wondering what basic rules of thumb you use to pick a potentially good night in advance. As for myself I go to these websites in order of precedence.

http://skippysky.com.au/Australia/

http://www.southerngalactic.com/AujetstreamLoop.html

http://www.southerngalactic.com/AUNOAALoop.html

http://www.southerngalactic.com/SGAusIR.html

Then I try to figure out
1/ if the clouds will get to me before it's dark enough to do anything
2/ is there's a jet stream overhead
3/ is the temperature below 20C warm nights don't seem to be any good
4/ look up and if the stars are seriously twinkling go watch tv

Some say it can be very good just after a rainy cold front has passed and some say just before. Not sure which works best as it probably depends on what's pushing the front. Haven't mentioned barometer readings but suspect they play a part too.

Anyway, fire away folks...teach me how to pick a good night.

Cheers
Stephen
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Old 13-02-2012, 06:37 PM
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Some nights are obviously better than others, for viewing, imaging etc.

I have imaged many a night and for me the best times were between 1am to dawn, on a cold frosty night, yep agreed it is very cold, as dark as it is going to get, but also very clear, and as the frost comes down the air is cleared of much dust.

But that is me, I love the frosty nights with a passion, probably not much help to you, but is my 2 cents worth.

Leon
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Old 13-02-2012, 07:36 PM
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BlackWidow (Mardy)
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Wel at the moment I use the it will do scale of forcasting. I go outside and look for a star. If I see one I thank a random God and get the scope out. If thier is only cloud I read astronomy books. Im reading at the moment and have been for weeks.



Mardy
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Old 14-02-2012, 07:55 PM
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Seeing is not the all important thing in some instances. It is for long focal length imaging but relatively unimportant for widefield imaging like with 600mm or less.

So if it is poor seeing you could still use a camera lens or a widefield scope to do some imaging and the result will still be fine.

Seeing is also dependent on the local topography and some areas have better seeing than others more often.

If you are limited to imaging where you live then of course that is not much help. But ultimately if your location where you live is where you image from it will be a limitation as will be your local light pollution.

In my experience west of the Great Dividing Range on the east coast of Australia seems better than east of the Great Divide. Not to say that area never gets a break because it does but less often.

Also clearer skies are more common to the west of the Divide.

How that applies to South Australia I am not sure. Probably inland of the Adelaide Hills is better than along the coast. Other SA residents could advise there.

Greg.
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Old 14-02-2012, 10:01 PM
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Forget skippy sky, I will state right here and I have years of documented proof that it is never right for seeing. I do mean never. It is seldom right for cloud cover, but that is another story. Nice idea, just the base data is not accurate.

Predictors for Adelaide area are often wrong as a whole. Some of the ones I use that are moderately accurate are

WXMaps

Unisys

Wundermaps use the shear plot under Model Data. This is pretty accurate.

Use these as a guide but the reality is looking for yourself through the eyepiece. Ensure that your scope is at ambient before assessing the seeing. Often people make assesments of seeing with a scope that has 3 or so hours of natural cooling and this is clearly not enough. Ambient active cooling is another topic but essential for seeing assessments and getting the most out of your optics. Bird and myself have discussed this here and elsewhere.

Greg has highlighted well the topographic factors for seeing. Southerly winds whilst viewing on the plains is not good for seeing. Good if you are south of the range though. Ray in Ardrossan gets good seeing when he gets easterly or south easterly winds. I get good seeing when a high pressure sits over the top of me and sometimes when mild southerlies pass over the ranges.

Overall though the best indicator for a chance of good seeing is when a high pressure lobs over directly over your observing position. Wind movement will mostly be non existent and the jet stream will be forced away from the high pressure.

Being a planetary imager I have spent years researching and discussing weather with most of the well noted planetary imagers here and abroad. Most would agree that the presence of a high is your best chance of getting good seeing, but often it can just come down to blind luck. Keep an eye on the sky and best of luck.

PS Read up on Damian Peaches site too for some good articles on seeing. My site and Birds site have tutorials on active cooling of optics. Also remember that the bureau cannot predict seeing even with the super computers they possess. The more I watch the weather the more I think luck and persistence pays off to viewing good seeing.
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Old 15-02-2012, 09:19 AM
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coldlegs (Stephen)
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Thank you Paul. Your local knowledge response was exactly what I was hoping for.

Forget skippy sky, I will state right here and I have years of documented proof that it is never right for seeing. I do mean never. It is seldom right for cloud cover, but that is another story. Nice idea, just the base data is not accurate.

I've been getting that impression too but have been reluctant to admit an astronomy weather site would be crap until now. In the bin it goes!

Ensure that your scope is at ambient before assessing the seeing. Often people make assessments of seeing with a scope that has 3 or so hours of natural cooling and this is clearly not enough. Ambient active cooling is another topic but essential for seeing assessments and getting the most out of your optics. Bird and myself have discussed this here and elsewhere.

Agreed. I bought one of those SCT coolers from this mob
http://lymax.com/sct/how.php
but haven't had the chance to use it yet as I'm still getting other bits and pieces together.
Have you heard of experiences with this type of cooler? Logically it would seem to work which was my excuse for buying it!

Greg has highlighted well the topographic factors for seeing. Southerly winds whilst viewing on the plains is not good for seeing. Good if you are south of the range though. Ray in Ardrossan gets good seeing when he gets easterly or south easterly winds. I get good seeing when a high pressure sits over the top of me and sometimes when mild southerlies pass over the ranges.

It's even worse up at Elizabeth. The weather hits the foot of York peninsula and funnels straight over me. If you ever look at a radar map of clouds heading east/north east you'll see it.

Overall though the best indicator for a chance of good seeing is when a high pressure lobs over directly over your observing position. Wind movement will mostly be non existent and the jet stream will be forced away from the high pressure.

Is there a night-time temperature caveat to that? I seem to remember a heat wave a while back where the night temperature was in the upper twenties/ lower thirties and there seemed to thermals everywhere.

Thanks for the websites and advice Paul.
Cheers
Stephen
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Old 15-02-2012, 09:24 AM
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Greg
Your absolutely right about focal lengths. I've been quite stubborn about deep sky objects and I need to get a scope with a focal length as you say of 600mm or less to maximize the cloud free nights which are few and far between. Also get some nebula filters as the light pollution is chronic around here.
Cheers
Stephen



Quote:
Originally Posted by gregbradley View Post
Seeing is not the all important thing in some instances. It is for long focal length imaging but relatively unimportant for widefield imaging like with 600mm or less.

So if it is poor seeing you could still use a camera lens or a widefield scope to do some imaging and the result will still be fine.

.
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Old 15-02-2012, 09:29 AM
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coldlegs (Stephen)
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Leon
I've got to admit some of my best nights have been when the water has been dripping of the scope and my legs are very very cold.
Cheers
Stephen


Quote:
Originally Posted by leon View Post
Some nights are obviously better than others, for viewing, imaging etc.

I have imaged many a night and for me the best times were between 1am to dawn, on a cold frosty night, yep agreed it is very cold, as dark as it is going to get, but also very clear, and as the frost comes down the air is cleared of much dust.

But that is me, I love the frosty nights with a passion, probably not much help to you, but is my 2 cents worth.

Leon
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Old 15-02-2012, 09:44 AM
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I used the Lymax cooler on my 9.25 years ago and these are certainly better than nothing at all. 20 minutes is not enough time though and you should use it for an hour before hand at the least.

High pressure does not always mean hot weather. Our seeing period really commences around mid March and ends in September for the Adelaide regions. There are the odd scattered nights outside this period but the thermal stability of the land is pretty consistent between those dates and you will find better seeing then.

Anthony and I have found though that the presence of the la nina system has the effect of speeding up the jet stream. This makes the weather systems move through too quickly and makes for really erratic seeing overall. You will need to have quite a bit of patience when it comes to viewing and imaging when looking for seeing. Right now and for the last month I have watched many good images of Mars and Saturn come and go, while I cannot capture a photon. I just have to wait my turn and that is what you will find too. If you are a member of ASSA I usually post a note in ASSA chat when the seeing is good. It has been some time I must admit.
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Old 15-02-2012, 01:16 PM
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Quote:
Originally Posted by BlackWidow View Post
Wel at the moment I use the it will do scale of forcasting. I go outside and look for a star. If I see one I thank a random God and get the scope out. If thier is only cloud I read astronomy books. Im reading at the moment and have been for weeks.



Mardy
I'm a bit like that too. There are so few cloud / mist free nights here that if it's clear you go out and image and take what seeing's on offer. If you don't do that you would never be out!

Neale.
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Old 16-02-2012, 07:16 AM
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At my dark site in NSW I find winter usually has better seeing than summer as a general rule.

If its windy I often find the seeing is worse/poor.

After a storm sometimes the seeing can be good. Its like all the energy is swept out of the atmosphere for a while.

Peter Ward has mentioned if there is fog and it clears seeing will be good.

I am not sure if there is a general rule about altitude but I imagine higher is usually better than lower especially if you are upwind of any mountains etc. You generally want even, flat terrain upwind of your location.
Less atmosphere to image through is better than more!

Islands that are fairly flat or islands with a mountain and the top of the mountain seem to be a good formula. Damien Peach likes Barbados and Barbados is quite a flat island compared to most others in the Carribean. You get smooth air flow over many kilometres of sea so it is flowing very smoothly.

I often wondered if coastal areas would be better if the winds were blowing from the ocean to the inland. I haven't heard anyone comment on this. Anyone know? Or is the surf haze and extra cloud in these areas more the problem?

Greg.
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Old 16-02-2012, 07:07 PM
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I've only started deep sky imaging in the last 6 months. I've soon discovered that gully winds are quite common this time of year. The persistent troughs in the east and high pressure ridges in the Bight, produce gusty E/SE winds an hour or so after sunset. These last until well after midnight. Many clear nights have been thrown out the window due to winds being above 30km/hr.
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Old 16-02-2012, 07:55 PM
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I belong to Martin's school of thought. If the sky is clear (fat chance ) and the BOM models suggest it will stay that way then I'll set up. The Australian models here generally have far more fidelity than NOAA models Skippy and others rely on. Still, Skippy usually gives a pretty good idea and we're lucky to have these tools.
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Old 16-02-2012, 08:11 PM
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Greg, seeing at Clayton is typically good when clear. The currents come up straight off the ocean all day and then abate an hour after sunset. There is nothing of any height from the ocean to Clayton which is only 6km. In fact most nights I can hear the waves crashing on the beach at the mouth of the Murray. That is how still it gets there. The down side to all this though is that during winter there is a lot of time with cloud and summer fogs are not unheard of either. That said I managed to capture 14 images from there last year and considerably more the year before. So imaging close the ocean can be very good for seeing.

Swannie, gully winds are starting to give me the pip this year. These have disrupted many attempts to image Mars and Saturn this year. The waiting game can be very irritating at times.
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Old 20-02-2012, 06:23 PM
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Thanks for that Paul. I often wondered about that. Australia has so much coastline and the winds coming off our oceans are often unobstructed for thousands and thousands of kilometres. But I can see fog and mist would be an issue sometimes. Also which way the winds are blowing another.

Greg.
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Old 20-02-2012, 11:51 PM
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Funny you should reply tonight. I am down at Clayton, with excellent seeing and viewing the clouds on Tharis (Mars) at 488 x through the eyepiece and then the clouds roll in. I am going to wait it out, but the seeing is very high quality and I might be onto a winner in a couple of hours.
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Old 21-02-2012, 05:40 AM
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I've tried all the forecasting sites & while they are somewhat correct on some nights, they are totally wrong on the majority of times. They are wrong that often I gave that all up a long time ago.

If it's clear, I'll preview the seeing naked eye. If a fast flicker is present it won't usually be any good for what I do (High rez planet imaging) I'll usually setup nonetheless because really, the only true way to tell is get the target on the camera livefeed.

Seeing comes & goes in patches where I am so it's still worth setting up in lousy conditions, especially in the month of Feb. (for me) On 6 nights in a row, I've seen it go from 5-9/10 within minutes & then back down to a 3/10. I have to be there previewing for HOURS before I'll get that good seeing data most times.

6 hours of previewing tonight/this morning until dawn gave me a result of Zero data captured. Dedication & plenty of time on your hands is paramount.
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Old 22-02-2012, 01:53 PM
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Quote:
Originally Posted by gregbradley View Post
Thanks for that Paul. I often wondered about that. Australia has so much coastline and the winds coming off our oceans are often unobstructed for thousands and thousands of kilometres. But I can see fog and mist would be an issue sometimes. Also which way the winds are blowing another.

Greg.
Just as a point of reference Greg, this image was taken at 11.5 meters at Clayton last night. Seeing was around 7/10 and about usual for the site. Clouds present and a bit of pain but on great nights all you get is great seeing (my best DSO's show that) and very dewed on. Wind always drops at sunset except if there is a low coming in. High pressures present winds during the day but once solar heating has finished at dusk then the winds fall to nothing.
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Old 22-02-2012, 03:48 PM
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I'm not sure if it is possible to have any reasonable seeing after about 12 am local time from here in the NE suburbs of Adelaide during summer.

I've done a lot of nights of long duration photometry, from twilight to twilight, and the trend is always for the FWHM to improve a bit from about 9pm to 11pm, then deteriorate steadily from there until dawn. I don't know, possibly it is something to do with the difference between the ground temperature and air temperature in a built up area. The one or two occasions where the seeing has been OK in the morning has been when the previous day was unusually cool.

Things seemed a lot more stable in winter, just that there were fewer clear nights (but actually I think this summer has been cloudier than the last).

-Ivan
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