Based on a numerical weather model, Clear Sky Charts are
perhaps the most accurate and the most usable forecasters of astronomical
observing conditions for over 6300 observatories and observing sites in
North America.
A color-coded map of the world showing sources and levels of light pollution
(man-made light that lights up the night sky and reduces what astronomers can see).
It is a mirror of David Lorenz's Light Pollution Atlas 2020,
but superimposed on Open Street Maps. Used by many to find good observing sites.
Used with permission
Computes the zenith brightness of the sky based on the altitude of the sun, altitude and phase of the moon, distance to the moon, solar cycle and a scattering model of the atmosphere. Computes the faintest star visible to the eye. Written by Ben Sugerman. Preserved here with his permission.
Offline Archive of Astronomy Forecasts
An offline archive of cloud-cover, transparency and seeing forecast maps from 2005 November to present.
Machine readable extracts, in csv format, are available for a fee. Data is available for any latitude/longitude withing the
coverage area, not just existing clear sky charts.