Since it's invention by Atilla Danko the clear sky chart has been giving amateur astronomers a quick and efficient means to see if the coming hours are holding special promise or will be just another night better spent indoors.
Every evening and night is accompanied with a combination of Cloud cover, Transparency, Seeing, and Darkness. Yes is may be obvious that good stargazing needs darkness and I should not need a web tool to figure this out, but what about seeing for instance.
Cloud cover, is simple enough.
Transparency, is poor when the atmosphere absorbs and scatters light. These actions will make the faint objects look even fainter and reduce contrast. Low contrast will wash out details of planetary viewing. Improved transparency will increase the number of deep sky objects that can be observed.
Seeing can either be good, to exceptional, or in the other direction just horrible. Exceptional seeing happens when the air of the atmosphere is calm. In this state, the lack of movement of the tens of kilometers of air that sky light need to pass through leads to incredible details in lunar, planetary and deep sky observing. Poor seeing, caused by significant turbulence, will obscure the details which can make for a disappointing evening out.
Darkness is simply indicating if the evening will be dark, the predictions given include moon light, which is enough to spoil your ability to see most of the interesting dark sky objects. Usually because the light form the moon keeps your eyes from dark adapted. Dark adapted is when your pupils are open wide and your ability to see in the dark is maximized.
There are over 3000 clocks on line for different places over the globe where CMC's data allows.
The above image is current and shows observation conditions for Ottawa Ontario for this evening.
Is it worth going out tonight?