Seeing and Transparency

Seeing and Transparency

Postby edward-fraini » Sun Aug 03, 2014 8:46 am

So what’s so complicated reporting seeing and transparency?

Let’s start with the simpler of the two. That would be transparency. Transparency is a measure of what you can see. That sounds simple enough. Most people refer to the little dipper as the gauge of transparency; others use common messier objects that happen to be in the sky that night. This latter method seems more prone to subjection to me because you are using a fuzzy object as the standard. A star should be a single point. It’s not because of that other factor seeing. There are two major things that drive poor transparency. Most people have to deal with the “darkness” of the sky which generally is a function of light pollution. The second factor is something people like us who live along the coast have to contend with. It is the amount of moisture there is in the air, or particulates from industries or Mother Nature. The droplets and particles scatter background light compounding the problem of light pollution. We have all seen the commercial where it is reported that the human eye can see a candle at the distance of 10 miles. Try that at Columbus as the air temp begins to approach the dew point. One of my favorite routines is to observe till about 11:00 or 12:00 then to go to bed and sleep for four hours or so. When you get up the dew has dropped and the clarity of the sky increases, hence better transparency. A clue as to how good the night will be is the blueness of the sky. You will notice we seldom have as blue a sky as you will see at TSP. So how do we fill in that little box on our observing sheet for the Astronomy Clubs that require it? How do you get to a number? I have talked to some pros who use a one to ten scale based on their past history. Some use the magnitude of the dimmest star they can see. In my opinion this is the best way and the way most all do it. Most often I cannot see all the stars in the little dipper so I need not look elsewhere. Therefore I might write in the box the “rounded” mag of the dimmest star I can detect. So the higher the number logged the better the sky condition is. Using this method I seldom see more all the stars in the little dipper at Columbus. Here is a trick I learned this year from one of the red hats at TSP that makes me a better observer. It can be confusing to look at Ursa Minor and remember what the magnitude of each star is. So this is what he taught me. In this constellation there are two stars at mag 2, one at mag 3, one at mag 4, two at mag 4.5, three at mag 5, one at mag 5.5 and lastly one at mag 6. You don’t have to remember which is which. Just count the number you can see. If you see one, go home and forget about it, , two the transparency is two, three it is three, four it is four, five or six it is 4.5, seven eight or nine and it is 5. Lastly if your where in a great spot and could see ten then it would be a 5.5 and you would be at the limiting magnitude for the average human eye. You can use this trick on whatever constellation happens to be up at the time you are observing.

Next post....Seeing- and it is a bit more complicated.

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