49 replies to this topic

[Androux]

Is there a way to judge "seeing" conditions quickly and easily without setting up your whole astronomy rig and conducting intricate tests?

Even better, is there a way to do that without leaving your armchair, some sort of remote camera set up outside with software that automatically evaluates seeing and notifies you when it's particularly good?

This is for backyard observing with a dob kept in a shed. It's not realistic to wheel it out every night, so I'd like to focus my efforts on the best nights.

Edited by Androux, 30 April 2025 - 09:41 PM.

[DeepSky Di]

Astrospheric?

[Jay_Reynolds_Freeman]

The more the stars are twinkling, the worse the seeing.

 

Clear sky ...

[Redbetter]

The simplest check is to look outside at the stars.  If there is little to no twinkle then the seeing is likely good, very good, or excellent.  Stars lower in the sky twinkle more, so if those are steady it is likely very good.  This has always worked for me as a seeing indicator, no matter the location.  

 

The problem with a dob kept in a shed is that a shed can be very hot in summer, so the primary is going to need some time to cool, with fan running, before it puts up decent images.  It is the sort of thing you want to start well before dark.  However, to do that you will want to have some idea whether the forecast is promising, so that you are not wasting time on nights that aren't likely to merit the effort.  I use Meteoblue's seeing forecast as a check.

[Jon Isaacs]

My two cents:

 

As Redbetter said, with a Dob, you want to have it outside and cooling with a fan before sunset.  Seeing predictions are notoriously inaccurate simply because there are so many things that have to go right and only one thing going wrong can ruin the seeing.

 

For me, the important thing is whether or not the skies are clear.  If they are clear, I will find something to look at with my 10 inch Dob.

 

Jon

[Tony Flanders]

Is there a way to judge "seeing" conditions quickly and easily without setting up your whole astronomy rig and conducting intricate tests?
...
This is for backyard observing with a dob kept in a shed. It's not realistic to wheel it out every night, so I'd like to focus my efforts on the best nights.

Are you talking about "seeing" in the narrow sense used by astronomers, or are you asking whether it will be a good night for using your telescope? "Seeing" in the narrow sense applies only to viewing objects at high power, like planets and double stars. With moderate apertures, seeing has little or no effect on the views of deep-sky objects. In that case, what matters is transparency, which is actually quite easy to judge with your unaided eyes.

 

You presumably live in an area with routinely clear skies. In my part of the world, nights without clouds are so rare that I want to take advantage of each and every one.

[Keith Rivich]

Is there a way to judge "seeing" conditions quickly and easily without setting up your whole astronomy rig and conducting intricate tests?

Even better, is there a way to do that without leaving your armchair, some sort of remote camera set up outside with software that automatically evaluates seeing and notifies you when it's particularly good?

This is for backyard observing with a dob kept in a shed. It's not realistic to wheel it out every night, so I'd like to focus my efforts on the best nights.

You could set up a simple imaging rig to give you an idea of the quality of the night. Take a few baseline images when the conditions are good. You can derive seeing and transparency from this base data when compared to subsequent images giving you an idea of current conditions. 

 

But iN reality it would be much simpler to wheel your dob out and just take a look.

Edited by Keith Rivich, 01 May 2025 - 03:53 PM.

[Freezout]

I think we see here some demonstration of the damage from these lengthy expert discussions nitpicking about quality of seeing, measuring every single factor of observing etc that we see on the forums. The death of spontaneous observation, and a member thinking that a clear night might not be worth it..

Androux, your dob feels alone in a shed, asking only to be loved and used as much as possible...

 

More seriously, as Tony and Jon said, you can always find something to be observed even in bad seeing. Most of the DSOs do not ask for high power and excellent seeing. If I would take my telescope out only when the stars are not twinking, it would remain in its closet the entire year. And still, I do a good part of Moon and double stars observation.

My real criteria: is the sky enough clear of clouds?

 

But God bless you if you have such a weather that you can afford to cherry-pick your nights when the sky is clear, and take the telescope out only when stars are not twinkling. 

[sevenofnine]

+1 on slow or no twinkling stars. That means little to no upper atmospheric turbulence  Then find either the Big Dipper or Cassiopeia. If the tiny star Megrez that joins the handle to the cup is clearly visible then the transparency is very good. Another good sign is being able to see all of the stars that form the W in Cassiopeia. If all conditions are met, don't walk to get your Dob...run!! 

Edited by sevenofnine, 01 May 2025 - 07:24 PM.

[Redbetter]

I think we see here some demonstration of the damage from these lengthy expert discussions nitpicking about quality of seeing, measuring every single factor of observing etc that we see on the forums. The death of spontaneous observation, and a member thinking that a clear night might not be worth it..

Androux, your dob feels alone in a shed, asking only to be loved and used as much as possible...

 

More seriously, as Tony and Jon said, you can always find something to be observed even in bad seeing. Most of the DSOs do not ask for high power and excellent seeing. If I would take my telescope out only when the stars are not twinking, it would remain in its closet the entire year. And still, I do a good part of Moon and double stars observation.

My real criteria: is the sky enough clear of clouds?

 

But God bless you if you have such a weather that you can afford to cherry-pick your nights when the sky is clear, and take the telescope out only when stars are not twinkling. 

 

Quantity does not equal quality.  An informed observer is likely to be a better and happier observer.  

 

There is an opportunity cost to wasting time on nights that are forecast to be bad for one reason or another (seeing, transparency, high winds, etc.)  That is what the OP is asking about, optimizing the time commitment for the best experience.  As I pointed out, there is some equipment prep time involved as well to make use of the sky. It generally isn't possible to have long sessions every night it is clear/forecast to be so, therefore picking the better nights has real value.  One has to schedule around life's other commitments, and often that comes down to picking the best night out of two or three candidates.  

 

Taking some time to look at several days worth of forecast and being able to recognize repeating weather patterns can make a big difference in picking the best nights while skipping the marginal ones. That is true for seeing and for transparency/cloud cover. Or one could use the spontaneous uninformed method and burn their time on a poor night instead, and miss the best night.  The difference is a memorable observing session, and a forgettable/regrettable one.  

 

It depends on the pursuit, but there are often "clear" nights that are not worth it.  Living here has proven that to me 100x over, I would definitely trade the vast majority of the "clear" nights here for a few nights with good seeing--even more so now that the backyard is twice as bright as it was only 6 years ago.  If your interest is planetary, lunar detail, or tight doubles (or aesthetics or observing near threshold) then seeing plays an out-sized role.  Poor seeing means a poor observing experience.   And despite claims to the contrary, it very much does effect small and medium aperture.  I have seen that many times in the backyard here.  In fact, an 80mm scope works well enough as a "seeing scout" for a night with useful seeing vs.one only fit for quick looks.  

 

I wish that as you suggest I could afford to cherry-pick nights to when stars are not twinkling at all, but that almost never happens here.  I have lived other places where it was not uncommon, but with fewer clear nights.  And for the type of observing I did in town, I much preferred those steady nights.  They were far more productive and rewarding.  

 

To illustrate just how much difference very good vs very poor seeing makes, there were some nights here a few years ago that produced the only fully stable seeing I have experienced in the valley.  They weren't clear nights, because there was a wildfire smoke plume high overhead.  This capped the night time thermal losses that drive much of the poor seeing during summer, so for several hours the planetary seeing was excellent.  As soon as the plume began to thin and shift out of the way the seeing began to decline.  This happened several nights in a row.

 

And this is without going into whether or not what appears to be clear sky at the moment is likely to remain so.  This is not as much of an issue for backyard observing (except when one can really only afford to observe one night or another and has to choose.)  However, it is huge for dark sky observing where one must pack up and drive out of town.  It isn't a lot of fun to have the skies begin to haze over, or go to full cloud just as one is finishing set up.  Those are real enthusiasm killers.

 

There are also dark sky sites that I rarely use anymore because they typically have poorer seeing.  My darkest local site is one of them.  It is only available for a few months each year and I have had some great sessions there.  But I have also had too many that I ended because the seeing became awful (katabatic winds).  I realized after a time that with most detail obliterated, there was no point in making poor quality observations of high quality targets.  Contrary to popular myth, seeing has a large influence on what is visible in galaxies.  

[Waynosworld]

If your telescope is easy to move/collimate then it will get used, my 20" F/3.7 is so easy to use I can wheel it out of my shed to my observing spot and collimate it in 5 to 10 minutes, if it is a bad night, a few minutes later it is back in the shed.

 

My shed has two roofs, one is the original sheet metal roof, the other is corrugated metal, it keeps it dry and cooler, of course it helps that the shed is in shadow in the evening, and it has a Hubble Optics Sandwich Mirror.

 

I have wheels on all my Dobs, it's like moving a large hand truck, but it takes time to make them easy to move this way.

 

[NinePlanets]

I'll toss in one other thing I've noticed: When high-altitude aircraft contrails remain steady and intact for a long time without dispersing, it seems to be a sign that upper layers are in a stable condition.

[LDW47]

How can anyone compensate for plain lazy, eh. There is no easy way out that will work like an ep and an eyeball, maybe.

[csrlice12]

If you wait for that perfect night....you'll be waiting practically your whole life.

[columbidae]

When the cat-sized mosquitoes are grounded due to heavy dew just after sunset, you know the seeing will be good - though observing in it at all is a different matter.

[daveb2022]

Besides cloud cover, I note twinkling stars (basic seeing levels) and NELM values (basic transparency levels). While NELM might be subjective depending on several factors, it is kind of a signpost IMO. Each site can differ vastly, but over the years I’ve also been able to see patterns and averages of what to expect from where I observe from most, which is my patio in suburban skies. That said, conditions can change over the night. If I were to rely on the astronomy forecasts, I’d miss out on many reasonable observing sessions. I don't have a clue what kind of skies you must deal with...just mine. It doesn't scare me out of setting up if Sirius is flashing like a strobe light or if my NELM level is below average... I can usually find something worth observing. Then there are those rare nights where the sky is a wreck. I look up and find something else to do.

[Tony Cifani]

That said, conditions can change over the night.

This. I've been out for a few hours with poor seeing with a few brief moments of stillness. Is it worth going outside with my telescope? Absolutely.

[Redbetter]

Seeing conditions often/most often change some during the night.  The better one knows their site, weather patterns, and how long it takes their gear to respond (being able to recognize thermals), the better one can prepare to take advantage of them. A smart/sane observer will select the better windows over the poorer ones.  Or one can spend hours sitting under poor seeing waiting for those still moments--despite knowing the odds are against it.  I've done it many times, they aren't coming.  It makes a whole lot more sense to target nights with more favorable conditions. "The definition of insanity is doing the same thing over and over again and expecting a different result."

 

I had an epiphany about this some years ago while observing in the typical poor/very poor seeing of the San Joaquin Valley.  I spent a lot of time at the eyepiece trying to understand why the seeing was poor or very poor most nights.  I learned to appreciate the characteristic speed of the seeing and how it differs on good nights vs poor or average ones.  Other folks from the valley didn't understand how poor the typical seeing was here, but in talking with them and through their descriptions of what they saw, I soon realized that what they called good or very good seeing was what I had found to be mediocre, and what they considered average was what I had long considered poor.  

 

This. I've been out for a few hours with poor seeing with a few brief moments of stillness. Is it worth going outside with my telescope? Absolutely.

This is an oft repeated and unfortunate piece of mythology based on a skewed reference frame. (I know this from decades of observing in regions with vastly different typical seeing.  What is normal in one is completely different in others.)  It doesn't describe poor seeing, it describes observing in good seeing that the observer unwittingly classifies as poor.  The tell is that in actual poor seeing, there are no "brief moments of stillness" unless the actual weather changes and the whole average shifts.  Poor seeing is fast seeing with changes far too rapid to track.  This can slow somewhat periodically, becoming less disturbed/mediocre, but it doesn't suddenly settle into still seeing.

 

Seeing tends to run in a channel most of the night.  It will drift a little into adjacent conditions at times, but it doesn't skip several channels instantaneously for a few seconds at a time.  I can often tell when the better moments or worse moments are coming by whether a breeze halts or picks up--it shows up rapidly in the eyepiece.

 

Very short still moments in the eyepiece can happen when the seeing is good overall, not very good, not excellent or perfect, but good.  The seeing is noticeably slower, but not steady.  When things settle and the image become steady it is quite noticeable, but in merely good seeing this doesn't last long, merely fraction of a second glimpses.  

 

On occasions when the seeing is very good the seeing is much slower, sometimes slow enough to manually track fine focus in real time.  At moments when this happens things become very still, the spaceship porthole effect, but they don't last more than a few seconds at a time, even if they repeat frequently. 

 

And then there is excellent seeing, when the diffraction pattern isn't moving, even at 8 or 10" of aperture, sometimes beyond that.  The porthole effect is constant for minutes at a time, and overall this can last for hours.

 

[Silent_Light]

Lots of twinkle, and if there are long contrails i dont bother.  Contrails are a measure of moisture in the air ( murky seeing)

[daveb2022]

  Other folks from the valley didn't understand how poor the typical seeing was here, but in talking with them and through their descriptions of what they saw, I soon realized that what they called good or very good seeing was what I had found to be mediocre, and what they considered average was what I had long considered poor.  

 

I have always been curious what other locals rate their skies at. What do you consider poor or average seeing for the Central Valley?

 

Whether it's my actual seeing ratings that are off, or if I do have better/poorer skies from what others believe makes no difference to me as long as I'm satisfied with the end results. IMO, I'm much more affected by poor transparency.

 

 

My backyard seeing conditions haven't changed much over the last 25 years using the same APO, & same EP magnifications I used in the early 2000's. When I compare observing from skies others astronomers consider premium (seeing wise), my location produces good results IMO. When I log seeing values as mediocre, I usually word it like "I'm having short periods of very stable seeing conditions." I also consider good as better than mediocre.

 

Perhaps it's lower expectations on my part? I do find my 4" refractor isn't generally able to be pushed past 240x on the larger planets and double stars, so would that be considered poor seeing conditions? I'm usually more than satisfied running my NP101 at 154x and on a good night of seeing, maybe up to 215x.

 

In most cases, how unstable the stars look visually, gives me an idea the seeing might be substandard, average or possibly above average. The OP is asking how to rate the sky w/o a scope or binoculars, so the twinkling stars method works but doesn't determine whether I set up or not.

Edited by daveb2022, 03 May 2025 - 12:52 AM.

[Asbytec]

Be careful, though, about stars that appear not to twinkle at all. Often that is not a sign for good seeing. The star is actually twinkling very quickly at a frequency we cannot see. So, it appears not to twinkle at all. That is a poor night.

 

A few years ago, I lived in the best seeing location I am aware of. Seeing was regularly 8/10 or better. Even the best nights the stars had a very slow twinkle. Maybe once a second or longer. They did not appear completely steady, but seeing was Pickering 8/10 or better. 

[Redbetter]

Be careful, though, about stars that appear not to twinkle at all. Often that is not a sign for good seeing. The star is actually twinkling very quickly at a frequency we cannot see. So, it appears not to twinkle at all. That is a poor night.

 

A few years ago, I lived in the best seeing location I am aware of. Seeing was regularly 8/10 or better. Even the best nights the stars had a very slow twinkle. Maybe once a second or longer. They did not appear completely steady, but seeing was Pickering 8/10 or better. 

While it is possible and reported by others, I have never seen that (no twinkle resulting in bad seeing.)    So I wouldn't call it often, I would call it unlikely--and perhaps observer or site specific.  I have many times seen no twinkle or little twinkle as very good seeing, primarily in humid East Texas, but also here.  And it has been one of the most useful quick indicators during a session while observing.  When conditions are running in the "good" channel, but not great, there is sometimes half an hour or more where the seeing becomes steadier.  I will look up from the scope and notice that the twinkle has become minimal, so if there are any well placed planets, I will switch to them.  And when the seeing begins to falter, a glance at the sky confirms the previous twinkle rate has returned.

 

My guess has been that this comes down to differences in people's ability to detect twinkle/flicker.  I am sensitive to flicker, some are not.  But there are typically other indications that the seeing will be awful, so it is possible that I am not even looking for twinkle during some of the worst cases--unintentional sampling bias on my part.

 

The Pickering scale that we use is actually Douglass' modified/improved version (defined for the 6" aperture he employed) which includes correlation to naked eye twinkle.  This didn't come from observations at a single site, it arose from observations at Arequipa (Peru), Harvard, Arizona and Mexico (near Mexico City.)  At the extremes are 1/10 with 33 twinkles per 10 seconds, and 10/10 with zero.  9/10 is 1 twinkle per 10 seconds.  

[Asbytec]

 

The Pickering scale that we use is actually Douglass' modified/improved version (defined for the 6" aperture he employed) which includes correlation to naked eye twinkle.  This didn't come from observations at a single site, it arose from observations at Arequipa (Peru), Harvard, Arizona and Mexico (near Mexico City.)  At the extremes are 1/10 with 33 twinkles per 10 seconds, and 10/10 with zero.  9/10 is 1 twinkle per 10 seconds.  

I wasn't aware of that study. I am glad someone attempted it. I am no expert on twinkling as it relates to seeing. I recall Frank arguing that twinkling (scintillation) and seeing are two different effects, but I agree there seems to be a correlation. I do not know what the correlation is if it is not windspeed at some altitude.

 

I do not think I have ever seen a night where twinkling has slowed to once every 10 seconds. I would not have waited that long. I have seen a slow flicker maybe once every second or two on very good nights. I remember being shocked on a very good night that I noticed any twinkle at all. 

 

I have also seen nights where scintillation was right at my limit of detecting it, and those proved to be bad seeing. Seems faster than 33 cycles per second, which shouldn't be that difficult to notice. So, it was a logical stretch for me to realize if I cannot detect a twinkle, seeing must be worse. 

 

Maybe it is site specific with some aspect of seeing differing between varying climates and geography. My situation is likely unique in that my best seeing was actually on the leeward side of (low level) 5,000' mountain range with a tropical north easterly flow off the Pacific Ocean. 

 

Linked here is maybe the best seeing chart I have found. Light blue and white are the best seeing locations. During our dry season, there is a persistent white area at 16N and 120E while the rest of the island endures higher windspeeds. Somehow the oceanic flow crosses the mountains and is unaffected. 

Edited by Asbytec, 03 May 2025 - 05:50 PM.

[rfcooley]

I think we see here some demonstration of the damage from these lengthy expert discussions nitpicking about quality of seeing, measuring every single factor of observing etc that we see on the forums. The death of spontaneous observation, and a member thinking that a clear night might not be worth it..

Androux, your dob feels alone in a shed, asking only to be loved and used as much as possible...

 

More seriously, as Tony and Jon said, you can always find something to be observed even in bad seeing. Most of the DSOs do not ask for high power and excellent seeing. If I would take my telescope out only when the stars are not twinking, it would remain in its closet the entire year. And still, I do a good part of Moon and double stars observation.

My real criteria: is the sky enough clear of clouds?

 

But God bless you if you have such a weather that you can afford to cherry-pick your nights when the sky is clear, and take the telescope out only when stars are not twinkling. 

I agree I think sometimes we get to carried away with what constitutes good or bad seeing, or good or bad anything.  Getting caught in the minutia creates a sort of a analysis paralysis that creeps in. When we are stuck in this trap we miss some good nights, some good targets, some simple enjoyment of the night skies.  It all seems to become to technically overwhelming  to do what we started out doing in this hobby, which was enjoying the night sky. Finding objects that were fascinatingly captivating.  I don't think most of us started out to learn all of the nuances and technical aspects of each object we observed. I know I didn't.

 

As to quality and quantity. I don't think we can arrive at quality without quantity of observations, and then the quality of our observations are very subjective. What is quality to me might not be quality to you. There are of course general principles that most of us can agree upon. The more twinkle of the stars generally indicates seeing is not as good as it is when the stars twinkle less. If I were to base my decision of whether to take out my scope only on the nights that I thought "twinkling" was acceptable to me (subjective) I could miss out on refining my experiences and the joy of just looking. There are always objects to see no matter how good or bad some parameter is or isn't. Now lets not take this to extremes. Obviously, if we are clouded out, raining, snowing or a category 5 tornado in the vicinity we can conclude that this is not a time to go observing. Mother nature does not wait on us. We have to wait on Mother Nature to resolve herself in such cases.

 

The advise I have for the OP is just go out and take a look. Bring a pair of binoculars if you wish, do a quick survey. Then decide what you want to do. To me if the conditions are decent. I will look around. Not because the sky condition are not perfect but just because I enjoy the vastness of the sky.  I keep a grab and go at the door just for this purpose.  So do many of us. Whether I observe for a few minutes or whether I end up out there for several hours. It is the chance to observe that drives me. Not whether the conditions are perfect or whether my equipment is good enough.  I wish to observe at any chance that I get.  It is rare that I don't learn something new or different from these forays into the night.  There are no perfect telescopes just as there is not always perfect conditions.  If I waited for perfect conditions I would not be able to use the equipment I spent a lot of $$ on. What kind of sense does that make?  Whether you spend a lot of $$ or not so many $$ what good is any of it if you don't enjoy observing with it. Don't get caught up in the technicalities. Get caught in the vastness of the sky. With quantities of observing you will learn what works for you and what doesn't. With many quantities you will learn what quality is to you.

 

Those of us that offer suggestion do so from our many quantities of time behind the ep or the camera.  The purpose is to give you some ideas to try for yourself. Your experienced should be based on what you find useful in all of the suggestions not stop you in your tracks. There is a smorgasbord of ideas and experiences here on CN. Don't be afraid to pick and choose as you see fit. Don't be afraid to ask questions. None of us have the perfect strategy or procedures that will work for everyone. The perfect strategy or procedure does not exist like the perfect telescope does not exist.

 

Clear Skies, Never Lose the Wonder

 

RF

[Jay_Reynolds_Freeman]

The question was whether there was a quick way to judge seeing; I hope the original poster does not get bored by the technical and philosophical discussions that grew out of the answers ...  :-)

 

Clear sky ...