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how to check seeing?

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#1 salico

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Posted 11 February 2019 - 03:27 PM

I ve been for a bit in this hobby now, but in some regards I still feel like a beginner. My plan is, to get some scope for planetary observing. My interest was previously DSOs, so different task now. How to check seeing, if your actual scope is smaller than the planned one? My biggest scope is an ED 120 binocular telescope, which gives 130x max with the N7. I live central in Germany and I can drive max 30 minutes to places and prefer my two DSO friendly places. I plan to observe the moon with it over the next 3 months to check, if it is worth at all to go beyond 120mm aperture. But how to know the limit? An APM 152 ED? Or a Mewlon 210? I think 8" might be the maximum...

 

Thanks for advice,

 

Sal



#2 Keith Rivich

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Posted 11 February 2019 - 03:50 PM

IMO there is no maximum aperture for planetary viewing. My 25" gives great views. Any of the scopes you list should be fine.


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#3 rk2k2

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Posted 11 February 2019 - 03:52 PM

I myself consider myself a beginner and I can't stress how useful Stellarium is to determine what equipment is  needed to provide the view you want or will get with the equipment you have.  Stellarium has an ocular view mode in which you can configure the various equipment, telescopes, eyepieces, barlows/ reducers, CCD sensor size (for astrophotography).  If you haven't used Stellarium, I suggest downloading and playing around with it.


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#4 happylimpet

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Posted 11 February 2019 - 05:05 PM

Cant beat a big newtonian for affordable high resolution imaging. Fit it with fans, and collimate well. You wont get a better image.  It's all about aperture.


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#5 salico

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Posted 11 February 2019 - 05:33 PM

but what, if the seeing is not good enough? btw, strictly visual...


Edited by salico, 11 February 2019 - 05:33 PM.


#6 spaceoddity

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Posted 11 February 2019 - 07:57 PM

but what, if the seeing is not good enough? btw, strictly visual...

If seeing isn't good then neither scope will show a lot of detail, but if the seeing is good then a larger scope will resolve more detail and be able to attain higher powers. The scope has to be cooled and well collimated for best results. I've seen significant differences in the amount of details on Jupiter between my 10" dob and my friends 12", side by side on the same night..



#7 SeaBee1

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Posted 11 February 2019 - 11:17 PM

How to check seeing (which affects ALL telescopes)? I go outside and I look at a bright star. In the winter season, that is usually Sirius (when there are no clouds, which here lately, it has been nothing but clouds...). If the bright star is twinkling madly naked eye, I know the seeing is bad. I will use low to medium magnification. If the star is pretty steady, seeing is usually good enough to bump up the magnification.

 

I have not found a reliable forecast tool to predict the seeing consistently, it is only determined by local, in the moment observation.

 

Good hunting!

 

CB


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#8 Napp

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Posted 11 February 2019 - 11:47 PM

How to check seeing (which affects ALL telescopes)? I go outside and I look at a bright star. In the winter season, that is usually Sirius (when there are no clouds, which here lately, it has been nothing but clouds...). If the bright star is twinkling madly naked eye, I know the seeing is bad. I will use low to medium magnification. If the star is pretty steady, seeing is usually good enough to bump up the magnification.

 

I have not found a reliable forecast tool to predict the seeing consistently, it is only determined by local, in the moment observation.

 

Good hunting!

 

CB

 

+1.  Not only is seeing determined by local, in the moment observation but it varies by region of the sky.  Seeing can be excellent near the zenith but will deteriorate as you drop toward the horizon.  For planetary viewing you typically want to observe when the target is as high in the sky as possible.  


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#9 Migwan

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Posted 12 February 2019 - 11:08 AM

Agree with comment on Sirius twinkling.   This time of year I go straight to M42 to see if E&F stars are both holding via direct vision.   If so, better than average seeing for me.  If F star not holding in direct vision, but E star holding well, good seeing.   

 

Problem is, you probably want to know this before driving to a dark site.  For that I look to local weather then to a regional satellite loop with upper, mid, and lower level IR and try to gauge how much wind.  Its not foolproof, but I seem to be getting it right almost all of the time now.  Since I am still in the DSO mode, I'll still go even if I think there are some upper level winds (but not the jest stream) if the humidity is low on all three levels.   I really don't leave home for planets, as they seem to burn through my moderate LP fairly well. 

 

jd


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#10 RalphMeisterTigerMan

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Posted 12 February 2019 - 11:23 AM

My more than half century experience has taught me the following:

 

1. If you cannot see ANY stars, it's probably overcast so try again in a few hours and keep checking your local weather - LOL!

 

2. If bright stars at about 45-degree above the horizon are steady and sharp, the seeing should be okay.

 

3. If bright stars at about 45-degree above the horizon are twinkling like crazy and not steady or sharp, this is BAD seeing, nothing will come to a sharp focus in your scope.

 

4. If the sky is hazy, then forget it. 

 

Hope this helps.

RalphMeisterTigerMan


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#11 Keith Rivich

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Posted 12 February 2019 - 11:25 AM

but what, if the seeing is not good enough? btw, strictly visual...

Then you stop down the scope to whatever works.

 

You can always make a big scope act small but you cannot, without getting into electronics, make a small scope act big.


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#12 REC

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Posted 12 February 2019 - 12:00 PM

I mainly use cleardarkskies.com to check for seeing conditions. Also a basic check on a couple of bright stars to see id they are twinkling. Sirius over 25* up is a good one and also Rigel.

 

The Trap stars are a good test as someone mentioned.



#13 Migwan

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Posted 12 February 2019 - 03:14 PM

Don't know about you all, but often I want to get to the dark before dark, so Sirius and friends haven't woke up yet.   cleardarkskies websites, as mentioned prieviously, are good for that too.   jd



#14 salico

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Posted 12 February 2019 - 04:26 PM

cleardarkskies seems not to work for German locations...



#15 kfiscus

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Posted 12 February 2019 - 04:50 PM

I use the calendar.  Seeing here is horrible November through March on the few nights that it isn't cloudy.


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#16 dUbeni

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Posted 12 February 2019 - 05:14 PM

Hello salico

I'm in Lisbon Portugal and use MeteoBlue. On the right there is a tab "special" and choose Astronomical seeing, it's not full proof, but is a good indicator.

https://www.meteoblu...ortugal_2270339

 

Clear skies

Bernardo


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#17 dUbeni

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Posted 13 February 2019 - 07:15 PM

Hello again salico

I also use this link for checking the location of Jet-Stream since is one the culprits for bad seeing

https://www.netweath...-data/jetstream

 

and this one for all the rest:

https://www.windy.co...32,5,i:pressure

 

Clear skies

Bernardo



#18 Myk Rian

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Posted 13 February 2019 - 08:33 PM

I use the Accuweather app on my phone to check the radar images. If it shows a promise of clearing, then I do the twinkle test on the stars.


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#19 salico

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Posted 14 February 2019 - 03:30 PM

strange observation tonight: Moon in my Lomo 80 BT at 20X very pleasant and sharp. At 68x clear scintillation. In my buddy's Zambuto 14" at the same time at around 200x a bit less scintillation. Cooling? His was properly cooled. My Lomo BT was riding in the car for 20 minutes and used for 30 minutes before that happened...

 

CS, Sal



#20 mikerepp

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Posted 15 February 2019 - 04:47 PM

A trick I have done over the years is to shine a green laser straight up.  Doing this I can judge how much humidity, particulates etc. are in the air.

 

One evening it looked perfect outside but for some reason seeing was horrible.  Did the laser thing and lo and behold about 500' above the ground was a layer of fog.  You could see the difference in brightness of the beam.  Hope that makes sense.   Its kind of a fun experiment.

 

Of course a twinkling star is always a good indication of poor seeing.



#21 salico

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Posted 16 February 2019 - 02:09 PM

thanks for the hints. Yesterday all methods say: bad, bad seeing, even at 40x visible scintillation!!! And I want to buy a plantetary scope?



#22 Pcbessa

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Posted 16 February 2019 - 03:03 PM

Seeing is dependant in temperature differences and wind. For instance. The sky may be clear but with the jet stream above, seeing mag be bad at high power.

Ideally:
Stable high pressure is a good start
Very dry and clear weather
No wind
Ideally a bit cold is good too
No light pollution
No moon. And ideally near new moon
Sun well below horizon

#23 salico

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Posted 16 February 2019 - 04:55 PM

some of those points never seem to happen here;-)



#24 NorthernlatAK

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Posted 16 February 2019 - 05:37 PM

Two nights ago my skies were beautifully transparent but the moon accepted no magnification. My 8" was out in the cold storage so it was properly cooled. The 25mm @ 48× looked like I was looking at it through boiling water! Stars were twinkling 45° above horizon. Temps were about -10F with no wind but seeing was abysmal! The higher up the stars twinkle the worse the seeing is. Very good indicator.

#25 salico

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Posted 16 February 2019 - 05:52 PM

Sounds a bit like my observation...




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