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Confused On "Atmospheric" forecasts?

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#1 jjbag

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Posted 05 March 2021 - 10:52 AM

Hey All,

 

According the the weather peeps.. tonight/Sunday night are suppose to be clear and cold. Yet when I look at Atmospheric forecasts I get confused by their forecast, I get cloud cover = 0% , Darkness very dark blue.. yet my seeing is suppose to be poor? huh.... not understanding why, i even look at the "forecasted movements" and the only thing i see is clear sky based of satellites..  I know the wind is to be 6mph with 10-12 mph gust (really not that bad here), I've seen this before where these forecasts have kept me out, yet my last "dog walk" when I looked up the skies were magnificent. Should I just ignore these "seeing forecasts"?

 

 

JJ


Edited by jjbag, 05 March 2021 - 10:52 AM.


#2 StarBurger

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Posted 05 March 2021 - 11:05 AM

The cloud cover may say 0 % indicating the sky is clear. This is not an indication of "seeing". Seeing is how badly atmospheric turbulence effects the steadiness of your image through the scope. Without a scope one can gauge seeing by how much "twinkling" is going on up there. On steady nights the stars barely twinkle but even in the clearest transparent skies the stars can be flashing like crazy.

Some of the best seeing I had was on a night with a thin high mist and barely a star visible and yet the seeing was so good I had the best views of Mars ever.

As regards reliability I recently had a forecast of clear all night and the satellite showing no cloud for 200 miles in any direction.

I set up and by 8 pm the clouds appeared from nowhere. Go figure.....


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#3 fmeschia

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Posted 05 March 2021 - 11:07 AM

Looks like the entire mid-Atlantic coast is under two jet stream strands. Jet stream winds kill seeing even in good transparency and cloudless conditions.

 

Screen Shot 2021-03-05 at 8.06.58 AM.jpg


Edited by fmeschia, 05 March 2021 - 11:08 AM.

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#4 AtlantaAstro

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Posted 05 March 2021 - 11:12 AM

The seeing and transparency are very different than just cloud cover. “Seeing” is atmospheric turbulence such as dust and microscopic debris as well as high atmosphere winds and conditions that may bend stars and make DSOs morph into blobs. Another thing to look out for is transparency which absorbs and scatters light which may make objects appear dimmer than normal. So just because there are no clouds, doesn’t mean conditions are great. And sometimes you’ll see great star gazing conditions but then it’ll be super cloudy. There are many factors to consider, all of which have to do with our atmosphere.



#5 csrlice12

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Posted 05 March 2021 - 11:15 AM

The cloud cover may say 0 % indicating the sky is clear. This is not an indication of "seeing"...

I set up and by 8 pm the clouds appeared from nowhere. Go figure.....

This is what happens when the dust plug is removed from the focuser or diagonal.  Clouds are attracted to photons and you released them when you removed the dust plug....could even be a full blown storm if you use an eyepiece as a dust plug as this focuses the photons.


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#6 jjbag

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Posted 05 March 2021 - 11:19 AM

Thank you all..

 

sigh.... 

 

well I'm off for a week with only 2 forecasted clear nights... thinking regardless of what the atmospheric forecasting's are telling me I have to head out.. before pollen season hits in a few weeks..



#7 Raginar

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Posted 05 March 2021 - 11:33 AM

Hey All,

 

According the the weather peeps.. tonight/Sunday night are suppose to be clear and cold. Yet when I look at Atmospheric forecasts I get confused by their forecast, I get cloud cover = 0% , Darkness very dark blue.. yet my seeing is suppose to be poor? huh.... not understanding why, i even look at the "forecasted movements" and the only thing i see is clear sky based of satellites..  I know the wind is to be 6mph with 10-12 mph gust (really not that bad here), I've seen this before where these forecasts have kept me out, yet my last "dog walk" when I looked up the skies were magnificent. Should I just ignore these "seeing forecasts"?

 

 

JJ

High level wind/moisture/turbulence.  Usually what your prediction shows for me is that my HFR will be poor because the star is bouncing around.  I've had it so bad in FL that I thought my mount was broken; next night I went out and the atmospherics were better and the mount tracked just fine.  

 

It's a forecast so it's not a guarantee; but if you're seeing weird effects... you know why.



#8 eyeoftexas

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Posted 05 March 2021 - 11:40 AM

Thank you all..

 

sigh.... 

 

well I'm off for a week with only 2 forecasted clear nights... thinking regardless of what the atmospheric forecasting's are telling me I have to head out.. before pollen season hits in a few weeks..

Good plan.  Just be prepared to adjust your targets for the conditions when you're viewing.  Clear Skies!


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#9 csrlice12

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Posted 05 March 2021 - 11:42 AM

A bad night viewing beats a good day working....


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#10 erick86

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Posted 06 March 2021 - 01:50 AM

Good plan. Just be prepared to adjust your targets for the conditions when you're viewing. Clear Skies!


Agreed! I have lists of objects that are still good to observe when transparency is poor, and others that are still good when seeing is poor. If both are poor then it might a binocular night just for fun.

There’s always something worthwhile to look at!
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#11 bikerdib

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Posted 06 March 2021 - 09:10 AM

You see what is over Texas, now you see my normal conditions.  I regularly deal with the subtropical jetstream.  I can say that in the last 48+ years I have never experienced excellent seeing where there is zero star twinkle.  With my scopes, seeing is ALWAYS the limiting factor when it comes to magnification.  Poor seeing conditions are for those deep space objects where low power views are best.


Edited by bikerdib, 06 March 2021 - 09:10 AM.


#12 kjkrum

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Posted 06 March 2021 - 11:54 AM

One of the best astronomy forecasts I've found is the Astrospheric app. But like the normal weather forecast, Astrospheric is accurate enough to be useful, but never perfect. I live on the west side of Tucson, on the east side of the Tucson Mountains. The weather in my neighborhood is chaotic. When Astrospheric is wrong, it usually reverses seeing and transparency. For example, it'll say transparency is excellent and seeing is average when I see a normal light dome and dead steady stars.

Edited by kjkrum, 06 March 2021 - 11:57 AM.


#13 kjkrum

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Posted 06 March 2021 - 12:04 PM

I have lists of objects that are still good to observe when transparency is poor, and others that are still good when seeing is poor.


What characterizes those lists? I've heard good seeing for high resolution (planets, doubles) and good transparency for high contrast (nebulas, galaxies) but I'm not really sure. I think I need to sketch more to compare what I see in different conditions.

#14 bikerdib

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Posted 06 March 2021 - 12:44 PM

Pretty simple really, for those dim, large objects such as emission, reflection or dark nebula the transparency is most important.  For small bright objects such as planets, Lunar, double stars and star clusters where you would use high power, steady seeing is more important than transparency.  Of course the condition requirements do overlap somewhat.  Then there are some objects such as brighter galaxies where you may require both to be good.


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#15 Dave Mitsky

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Posted 06 March 2021 - 01:11 PM

There's information on seeing at the following URLs:

 

http://www.damianpeach.com/seeing1.htm

 

http://www.damianpea...m/pickering.htm

 

https://skyandtelesc...ing-the-seeing/

 

https://www.skyatnig...nomical-seeing/



#16 jjbag

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Posted 06 March 2021 - 02:50 PM

Good plan.  Just be prepared to adjust your targets for the conditions when you're viewing.  Clear Skies!

In theory it was, in practice it was a horrible night. As I put up my blinders to block the left side neighbors lights and began observing (LOVED that I got to spend time with my old friend Orion) my right side neighbor has had some upgrades to his backyard entry way and his stand alone garage, both now have motion sensor lights that pick up my movements . After an hour of frustration I called it a night (and now I wait for my prime deliver of more  Garment Rack and Tarp (perfect rolling blinders) will be here Monday .. and Tuesday is suppose to be another clear night. When at first a neighbor blinds you, try, try again.

 

JJ


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#17 alphatripleplus

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Posted 07 March 2021 - 12:33 PM

Hopefully Astrospheric predicts it will be clear after you get the new blinders, and the prediction is accurate.smile.gif




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