Clear Sky Chart

Clear Sky Charts (called clocks until February 29, 2008) are web graphics which deliver weather forecasts designed specifically for astronomers.

There are clear sky chart forecasts for over 6100 locations, though the coverage area is limited to Canada, the USA and parts of Mexico and the Caribbean.

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.

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".

[5] Danko's attorney opined that he was not infringing Skyclock Company's trademark, but also advised that changing the name was the "least painful" and least "expensive" solution.