Friday, August 31, 2007

Many amateur observers of the night sky can be more than slightly frustrated by the local weather forecasts available to them. The usual Environment Canada forecasts, for instance, lack both specificity and accuracy. It does you little good if you want to see if an event that will happen around 5:00 am to know that the forecast for that night is "variably cloudy". Very nice. Molly has mentioned a website previously that provides a much better forecast for those who are interested in viewing conditions. This is the ClearDarkSky site. It is the creation of two Ottawa amateur astronomers, Attilla Danko and Allan Rahill. The latter works for the Canadian Meteorological Centre in Ottawa and has put his weather forecasting talents to work on this website. Danko created the computer programs that allowed Rahill's weather maps to be translated into viewing forecasts for specific localities. To read a general overview of their collaboration and the result see .
Stated succinctly the ClearDarkSky site is a web resource that can give amateur astronomers very specific, hour by hour, forecasts for 48 hours of a number of viewing conditions that affect you ability to see what is in the skies. The data provided is much more specific than that provided by the usual weather forecasts. There are a total of 3188 'Clear Sky Clocks' for various locations across North America, 547 Canadian, 14 Mexican, 1 Bahamian and 2626 American sites. In many cases the data presented has a very much finer "resolution" than that presented by the usual weather forecast. Forecasts are delivered for points as close as 25kms apart. The forecast is also arranged as an "hour by hour" presentation.
What is presented in the forecasts ? Once more a lot more than the usual weather forecast. The colour coded bar presentations present forecasts for cloud cover, transparency, seeing (a composite measure that depends on many conditions), darkness, wind, humidity and temperature. All of these may affect either what you can see or your simple comfort in observing. All that Molly could think of adding would be a biting insect forecast. The only complaint that Molly has about the site is that the colour coding can be a little hard to read. I find myself sticking my face about 8 inches in front of the computer screen to try and see exactly what colour each hour block is, particularly in the "cloud cover" row. But that quibble is minor in light of how valuable such a well defined forecast is.
The ClearDarkSky site is not just a viewing forecast aid, though that would be a treasure in itself. Each locality listed has links to Sun and Moon data, road, topological and satellite maps, a star map link and even a "Clear Sky Alarm clock" that can alert anybody at that locality about upcoming clear sky viewing conditions. The main site has links to North American astronomy clubs, planetariums, museums, observatories, the Royal Astronomical Society of Canada and its various branches, star parties and other things that might be of interest to the serious amateur astronomer such as dark sky preserves, astronomy villages, campgrounds and wildlife centres.
There is even an invitation to participate in Allan Rahill's ongoing project to improve the "seeing" forecast with more and more real data from collaborators across the continent. This is the North American Seeing Observation Program. Astronomy is an area of science that actually has a large input from the non-academic amateur, and this is one of the many projects that are ongoing in the field.
So...drop by ClearDarkSky for a real treat.

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