Is seeing important for the deep-sky observer?

What is your experience and opinion?
Of course, seeing is important for resolution of distant globular clusters, but what about galaxies and extended nebulae?
Personally, I consider good seeing to be a great advantage, almost regardless of object. If the seeing is VERY bad the stars look like 2 - 3" fuzzyballs, and even low magnification images suffer. I assume that this doesn't affect objects like the North America Nebula very much, but the nice impression of the faint nebulosity embedded in the rich field of pinpoint stars is lost.
I can't say for sure how small features I can make out visually in a galaxy like M51. Anyhow I always have a feeling that it looks unsharp at higher magnification (150 - 200x is often a good choice for this galaxy). And I'm never satisfied with an observation of M81 if I can't split the two small double stars in the field.
I also believe that poor seeing reduces the ability to detect very faint diffuse objects. Reduced resolution means reduced contrast. Thus a very faint object, otherwise possible to see, can disappear when seeing is bad.
What do you think?

Inge S

Inge Skauvik said:
I also believe that poor seeing reduces the ability to detect very faint diffuse objects. Reduced resolution means reduced contrast. Thus a very faint object, otherwise possible to see, can disappear when seeing is bad.
What do you think?

It depends. If the object is small, that can certainly happen. If the object is large, however, all that happens is that high-frequency features are swamped, but the object as a whole can be detected almost as well as it could without the atmospheric turbulence. The acutance is compromised, but at low powers (which will be used for mere detection of large objects), this won't matter as much.

I have found seeing is always important and great to have. It is important in globulars, PN. I have done alot of deep sky observing at the limit of my equipment and find that detecting faint objects and detail is seeing related although I think transparency is probably just a shade more important. Details in galaxies very seeing dependant. Several of the objects I have chased have been seeing dependent.

Kevin

Hi all,

Many good points. Locating small planetary nebulae is very difficult when seeing is bad. I normally consider seeing as "bad" when the star images at my lowest magnification (63x) are clearly diffuse. Then the star images are cotton balls with 2 - 3" diameter, and as such all of them looking more or less like small planetaries. Blinking with an O-III filter may help finding the objects, though.

Extended diffuse nebulae like the Pelican Nebula or North America Nebula definitely suffer the least, but the aestethical impression is not the same since the stars look unsharp.

Many of the obscuring clouds and emission regions in distant galaxies are small in extent, and will definitely be washed out by poor seeing. One of my best sights ever of M82 was with the 8-inch Portaball under excellent seeing conditions and a magnification of 170x.
Another sight to remember was the Eskimo nebula with my friend's 18-inch and O-III filter, once again under superb seeing. At a magnification of around 250x we could enjoy the delicate features of the nebula. We have returned to this nebula later without being able to make out half as much detail.
I also think that seeing is very important for detecting the spiral structure of small face-on galaxies like M99 and M61. I find it very difficult to see much detail in these galaxies at 63x magnification. About 200x is much better, and the features of these objects are very delicate and need very stable seeing for a good view.

Inge S