As you all know, I’m quite the minimalist when it comes to observing gadgets. I have my trusty observing duffel bag stocked with the basics. I’ve often said that if it doesn’t fit in the bag, I don’t bring it. The basics (to me) are: batteries, rubber bands, red flashlight, star charts, binoculars, towel, pencils, hand and toe warmers, green laser pointer and last but not least, the clipboard.
The clipboard is a key piece of equipment! On it are several important observing tools that help with every session. I have some blank paper and some preprinted observing forms. Evaluating the conditions of the night sky, namely the ‘seeing’ and the ‘transparency’, is an important part of the night, but it took me awhile to keep them straight! So included on the clipboard is my favorite cheat sheet, the Seeing Conditions chart. (See our Links and Resources page)
Seeing has to do with the condition of the atmosphere itself. Humidity can make the images dance and twinkle, or sometimes they’ll alternately blur and clear. Assigning a number to the current seeing conditions is made easier by the descriptions on the chart. Keep in mind a perfect 10 for seeing conditions is rare! I think the best seeing conditions I’ve seen is a 6 or 7!
Transparency has to do with the limiting magnitude of naked eye objects. In other words, what is the dimmest star you can see with an unaided eye? This can be different from person to person, for example, my night vision not a good as Lynn’s. The Little Dipper is a good constellation to use, as it has a large range magnitudes contained within it.
As you can see, it ranges from magnitude 2 which is Polaris, to magnitude 6.7. Most people can see down to around magnitude 6 with an unaided eye, in dark sky conditions. You’ll notice that some of the magnitude markers do not have a decimal point. This is how they are supposed to be recorded, so the decimal point is not mistaken for another star.
So- why do we take the time to make this evaluation? Well, most observing
programs require you to record these conditions with your observations. Even if
you aren’t working on an observing program, it’s good practice to make this
observation. I believe it makes me a better observer.
I hope this helps your next observing session! Feel free to print it and make it part of your observing arsenal! We use it every time we go out!