Learning - Seeing

03/21/08

When I first got my telescope, I was all eager and anxious to begin seeing the night sky in a new way. I had done some basic naked eye and binocular observing, but I have severe gadgetitis. If I like something, then I want all the toys for it. Gadgets get me even more interested in hobbies, so it is something of a vicious circle. :-)

In any case, I started off right off trying to both observe and take photo's causing some predictable newbie errors. But I must say it has been great fun!

So here are some of my errors and adventures..

	First off, I live in the Seattle area. Fabled for its long months of rain. While it is not always raining, during the winter it is often cloudy.
	Next, there is the matter of finding dark skies. I live outside town, so I can get reasonable skies compared to town. I was thinking that I was all set.
	Then I actually tried to find and look at something. We have a great 'Chalet' type house in a nicely wooded area. The problem is of course that trees tend to block even more light than clouds when they are in the way. Let me tell you, a 100' tree can block a lot of sky. I found I need to time things so that the object I want is in my 'clear patch' of sky. The program Cartes Du Ciel is a great help for this!
	So I finally get a clear night and I know the object I want to see is in my 'window' between the trees. I set up the scope and.... Now how do you set this thing up anyways...? My telescope has one of those great computerized GOTO functions. It is on a Alt/Az mount, but how do you align it so the computer knows where it is?

Well for you non-astronomers, the answer is to use 2 stars to align the scope. By pointing to a couple of known stars, the computer gets oriented. This little step caused its own problems. You can read about it when i write it up. :-)

Finally, it is all ready, I have my euipment all set up, good skies and a simple object to start looking at. In this case I selected the moon. It is nice and bright, easy to spot, and should be really easy to get video/photos of. (Since it is so bright.)

So Finally I am getting video - but I encounter poor 'Seeing'. Take a look at the video images below. You can see the shimmer. The moon surface gets distorted and seems to flow around. The edge of the moon gets visible bumps in what should be a smooth curve.

The shimmer, smearing and distortions are all caused by the atmosphere. Air turbulence or changes in air temperature can cause the air to act as a lens. You can image the slight lensing effect of many little pockets of air in the observing column.

So what do you do about that? Well here are some steps you can take.,

	Let your telescope cool down to ambient temperature before observing. This is especially a problem with SC Telescopes I am told.
	Use a shorter focal length. Basically for less magnification , the same amount of shimmer looks to be a lot less. Fortunately the moon is a big object so less magnification works.
	Get LOTS of video or still frames. Usually the seeing gets a little better and worse over a split second. Some frames will look better, some worse. Use the better frames..
	Observe brighter objects so that you can use a faster shutter speed. This will let you get less of a smearing effect by freezing the shimmer in place. It also means that you have a better chance of getting some good frames.
	Use stacking software to stack lots of the good images to 'average out' the problems.
	Do not observe around any sources of heat. For example observing from beside a house, or looking over top a hot tub can cause local turbulence.
	Look at other objects that do not suffer from the same problem. For example DSO's can look good even though there is a fair bit of turbulence.
	Finally, you need to wait for better weather.

This site was last updated 09/10/04