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Clear Sky Charts (called clocks until 2008-02-29) are web graphics which deliver weather forecasts designed specifically for astronomers. They forecast the cloud cover, transparency and astronomical seeing, parameters which are not forecast by civil or aviation forecasts.〔A. Danko., "'A Weather Clock for Observers'", Sky and Telescope Apr 2003; 62; ()〕 They forecast hourly data, but are limited to forecasting at most 48 hours into the future. Each individual chart provides data for only a 9 mile radius, and so are essentially point forecasts. There are clear sky chart forecasts for over 4500 locations, though the coverage area is limited to Canada, the USA and parts of Mexico and the Caribbean. Locations are typically cities, professional and public observatories, colleges and science centers. However there are also clear sky charts for star parties and backyard observatories. ==History== In 2000, Allan Rahill, a meteorologist at the Canadian Meteorological Centre (CMC), created a forecast processing step that took data from CMC's Global Element Multi-scale (GEM) forecast model and created a new forecast of cloud cover.〔 *Ivan Semeniuk., "STARSTRUCK: Clear Sky Clock", Daily Planet, Discovery Channel. April 15, 2005〕 Rahill specially designed his cloud forecast to consider the formation of cirrus clouds. The cirrus cloud modeling distinguishes Rahill's model from other cloud forecast models, as sufficient cirrus clouds to make a night unusable for astronomers is still called "clear" by civil weather forecasts. In later years, Rahill added a forecast of astronomical transparency, which is a measure of how much starlight traverses the Earth's atmosphere when otherwise free of clouds. Rahill also added a forecast of astronomical seeing which uses forecast data of turbulence and temperature gradients in the atmosphere to forecast its optical steadiness. In 2001, Attilla Danko, computer programmer and amateur astronomer, began to summarize Rahill's hundreds of forecast maps by displaying only one pixel, from each map, laid out in rows.〔Lydia Lousteaux., "'Interview with the creators of the Clear Sky Clock'" astronomytoday.com; ()〕 The resulting meteogram, called a clear sky chart, showed all of Rahill's forecast data, but for only one location. Danko writes "It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site". Danko accepts requests from observatories and private individuals to create new CSCs for locations not currently covered.〔"The Clear Sky Clock" Sky News magazine. #54 | Volume IX, Issue 6 | March/April, 2004〕 However, since CMC's GEM model only covers North America, CSCs are limited to North America. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Clear Sky Chart」の詳細全文を読む スポンサード リンク
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