Clear Sky Chart
Be a Sponsor
ContentsFind a chart
News (October 17)
Meet the Perps
Your own chart
URLs & Server Status
Silly Files (Jan 5)
Boring Admin Stuff
How to Help
What is it?It's the astronomers forecast. It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site. There are many, but the example above is for ().
Read from left to right. Locate a column of blue blocks. That's when the sky will likely to be clear and dark. A more detailed explanation is here, but the short version is: the clear sky chart predicts hourly cloud cover, atmospheric transparency and seeing. (Good "seeing" occurs when the air is steady enough to allow you to see fine detail on planets through a telescope.) That means you can plan whether to observe galaxies or planets or stay home and process image data.
If you find this image, or the underlying forecast maps, useful please email Allan Rahill. He needs to show his bosses at CMC that his astronomy forecasts are actually being used. Feel free to copy me.
Are there Charts for other locations?Yes, thousands. The coverage area is Canada, USA and parts of Mexico.
May I get my own Chart?
If you observe at a site more than 24km or 15 miles from an existing chart site, feel free to request a chart for it. You can find the closest chart site to a latitude/longitude here.
I can generate charts for almost anywhere in Canada and US. See the coverage map.
To ask for a CSC, email me with:
I reserve the right to offer you a different chart that is still close enough to give maximally accurate forecasts.
There is no cost. But you're welcome to sponsor.
Copyright 2017 A. Danko. Page updated 2017-12-15 02:06:36UT on server3.