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Best locations for sub-arcsecond daytime seeing

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#1 Spot On

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Posted Yesterday, 10:02 PM

So, I am on a much-needed vacation in Puerto Vallarta, Mexico, and I didn't bring a solar scope but I did bring an AiryLab Solar Seeing Monitor because various family want to live here and I wouldn't want to move someplace worse than where I live now.

 

RN I live in San Francisco, which is at 37.5°N, and about the best daytime number I've seen on the SSM is 0.4 arc-seconds but I have never seen the 1-minute average get below 1".

 

On a lark, I took some measurements right at the edge of the ocean in PV at about 3:30 in the afternoon in light winds, expecting the worst, and was astonished to get a 1-minute average of 0.664 arc-seconds!  Of course at this latitude of 18°N the sun hits the zenith rather late, at almost 2pm, so at that time the sun is still quite high.

 

Measurements on the hot sand were still pretty acceptable with a 1-minute average of 1.2 arc-seconds.

 

Measurements on the roof of the place I'm staying were a lot worse, over 2".

 

Before this the best seeing I've got is on hot, still days in SF with at least 50 feet of grass south of the scope.

 

Altitude doesn't seem to make any difference on its own.

 

This is the first time I've seen proximity to water make such a big difference.

 

Where do you go for the good daytime seeing?!

 

 



#2 cimar

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Posted Yesterday, 10:11 PM

In the early morning the seeing is much better and the solar images are so much sharper than later when the sun is higher in the skies.



#3 AstroBrett

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Posted Yesterday, 10:13 PM

Many of the best solar observatories are on lakes where the seeing is superior. The water stays cool and you don't get the turbulence like you do from heated ground.

 

Brett


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#4 siriusandthepup

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Posted Yesterday, 10:37 PM

Kitt Peak National Observatory in Arizona might be in a good location.

 

I don't know any seeing details, but the day I visited I experienced the most amazing transparency I've ever witnessed. Standing below the solar telescope - using it to block the sun at mid day - the edge of the observatory that I used to block the sun was approx 75 feet from my eye.

 

I only had to move about 1 cm left/right to obscure the sun or let some sunshine into my eye. When obscured by the building - it was impossible to tell the sun's location. That haze area we usually see for 3 or 4 degrees all around the sun in the day time was absent - as in Zero, Nada, Zip, none! Totally blue sky to exactly the edge of the sun. I have never seen that before or since. Hope to visit again someday.

 

I suspect that the daytime seeing was the guiding factor to site selection for the Solar Telescope. Guessing the transparency was a bonus.


Edited by siriusandthepup, Yesterday, 10:39 PM.


#5 GSwaim

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Posted Today, 12:12 AM

In my opinion, late morning through early afternoon is the best times for solar observations. 

Location wise over a body of water like a lake or a beach is ideal when it's not too windy and/or super cold or super hot outside.


Edited by GSwaim, Today, 04:13 PM.

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#6 HPaleske

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Posted Today, 02:54 AM

...

Seeing is a very complex matter.

 

The best locations are those that are very dry (little water vapor in the atmosphere) and have homogeneous air movement.

 

The terrain should not have much unevenness if possible. A slightly hilly landscape is advantageous.

Many mountains with southern slopes heat up strongly and release the heat back into the surrounding area. This is not an advantage for the seeing.
On Tenerife, the solar observatories are located on the west side of the island, since a steady air flow comes from there.

In addition, the local and temporal conditions play a major role.

 

In my location, light winds are of great advantage in the summer. About 2 seconds after a gust of wind, the seeing calms down significantly. I cover the black balcony railing in front of the Unigraph with a white cloth. This way I reduce the local heating. The telescope is also in the wind, so that the lens can always be blown free.

 

However, if I get a current from the east or north east  (from Norway or Russia), all the local changes are of no use at all. The seeing is then too poor for high-resolution images. This is especially true in the summer.

 

You're doing it right, you have to measure turbulence on site and do it over a long period of time spring through fall.

 

 

cs Harald

www.unigraphprom.de


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#7 ch-viladrich

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Posted Today, 01:28 PM

The reason why you have good seeing near the ocean in light wind, is that the air flow is laminar. When the flow is laminar, it is not turbulent ;-)

Hence the excellent image quality at Big Bear (on the shore of an artificial lake).

Still, the wind has to flow over the water body before reaching the telescope.

 

In any case, this is a good idea to check places and time of the day with the SSM. After a while, patterns will emerge and you will identify where are the good places and when is the best time;


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#8 chemman

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Posted Today, 01:50 PM

For my location in the high country of Colorado the best seeing conditions I have seen were from 12,000 feet above sea level with the jet stream not streaming over my perch.  Did not have my SSM but quivering and undulations were mostly imperceptible.  Phenomenal.  

 

chuck



#9 MalVeauX

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Posted Today, 03:27 PM

Hi,

 

While there are geographic and atmospheric places with likely best seeing opportunities, we don't have access to them always and few live at these places. If you're willing to travel for best seeing, there are lots of great places, but kind of a moot point unless you're into high res imaging. Looking for excellent seeing conditions for visual is one thing, but for imaging, it depends on how you're sampling and your image scale. You don't have to go to some super special place to essentially cap out the seeing needs for an 80mm for example or even a 102mm. It's only with the larger apertures, I'd venture to say 150mm or greater, that you may have to start looking for places with excellent seeing to use these (unless you live somewhere with good seeing) and if you want to use large aperture, from a solar perspective, like 250mm+ apertures, you need observatory class locations essentially for seeing conditions. So if your interest is high res like that, then sure, you may need to find locations to attempt at. For smaller apertures, you can probably just learn more about your local seeing environment and find out when your best seeing is during the day at your specific location, unless you just have really bad seeing conditions year round (like sitting in the jet stream constantly).

 

I'm in Florida, closer to the North Western swamp edge near Cedar Key. Not known for anything in particular, like South Florida seeing conditions. But I still have pretty good seeing conditions usually. Mine are ideal early in the morning as the sun is rising, low on the horizon, and improves again before sunset typically. Depends on summer vs everything else as temperature delta in the day plays a role, moisture in the air plays a role, wind direction, clouds at different elevations, etc all play a role. And funny enough, storm season usually has good seeing, despite all the clouds and rain. Big systems moving in generally push other systems around and that directional flow can result in great seeing. So as a hurricane front moves towards us or leaves us, I can usually get really excellent seeing between the storms, provided clouds are not remaining. But, my every day seeing is more interesting to me. I don't care to get a high res image once per year. I'd rather just get an image any particular day I want to image, and I just try to image to the seeing conditions I have that day. So to make it a lot easier, the SSM really helps. Less gamble, more predictable results, and I can pretty much image to the seeing ceiling any particular day in 30 minutes to 45 minutes with several wavelengths, both full disc and moderate to high res depending on the seeing. I like fast sessions like that, rather than gambling and fussing with things without knowing what the seeing is doing on a particular day. For my local seeing conditions, I try to make sure I eliminate as much local modifiers (wood surroundings, white colored surfaces, my mount is over 1 meter in the air on a tall pier, my metal bits are covered with reflective surfaces to avoid becoming heat-sinks, I run a fan under my equipment to keep directional flow under my imaging OTA, etc). And I run my SSM so I can see what my seeing is doing.

 

If you want to maximize your living location's seeing, simply measure it a lot. Measure it over the year. And keep doing it. You'll build a database for yourself. You may find there's a relative time area that has the best for your location. It may be more than once a day. But instead of guessing, you can measure it and see what it is. Then you can plan around that.

 

I've been measuring mine a while, and for my location, just after sunrise in the summer and fall, my seeing is best. Sub-arc-second best. Then it falls apart towards later morning. Then it improves again by evening towards sunset. Mid-day is my worst seeing, always. But, in the winter and spring, my seeing is not so good early morning and actually improves to its best in the late morning towards afternoon. Then it's bad until late evening towards sunset, and never really gets great again but at least gets better than mid-day.

 

Here's an example of my fall early morning seeing when it's near its best, sub-arc-second for nearly an hour, hovering that 0.6~0.8 arc-second average per minute with better spikes range that will support 200mm aperture in red wavelength and 120~150mm aperture with shorter wavelength.

 

SeeingConditions_08022020.jpg

 

Here's a spring late day seeing, when it's better in my later part of the day (shorter days in spring here), in case I miss the morning attempt due to weather. Still sub-arc-second, but not quite as good as my summer/fall morning seeing. So this is more 150mm aperture seeing in red, and 80~102mm aperture seeing for shorter wavelength:

 

BestSeeing_LateDay_LowAlt_01152020.jpg

 

So that's just to show how twice a day I could make an attempt with potentially good seeing and image at that seeing potentially, but it came from measuring it a lot. You can do it of course by eye and just image or visualize seeing yourself, but I find that too tedious and that having the SSM just doing its thing with no effort on my part hardly is so much more convenient and I can share graphs and refer to graphs and data which is a lot better for sharing and conversation about this stuff.

 

Very best,


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