What Makes a Good Astrophotography Forecast?

Low or zero cloud cover is the minimum requirement for astrophotography. But cloud cover percentages from standard forecasts often mask what's happening at different atmospheric layers — thin high cirrus is very different from a solid stratus deck at 3,000 feet. StarCast scores cloud coverage across all atmospheric layers and reflects whether that cloud cover actually blocks the sky or merely reduces contrast.

Transparency is the most underrated variable in astrophotography forecasting. High humidity, wildfire smoke, sea salt, and fine aerosols all reduce transparency — creating a technically cloudless sky that still produces dim, low-contrast images. Post-frontal air after a cold front is the gold standard: the atmosphere cleans out, stars snap sharp, and dynamic range in your exposures visibly improves. StarCast scores transparency for every forecast.

A full moon adds roughly as much light to the night sky as significant urban light pollution. For wide-field Milky Way work, anything above 40–50% illumination is effectively a wasted night. Even for deep-sky imaging on a telescope, bright moon raises your noise floor and limits exposure time. StarCast shows moon illumination, rise time, and set time for every location so you can calculate your true dark window with precision.

Even a perfect forecast can't overcome severe light pollution. At Bortle 7 or above, wide-field deep-sky work is marginal regardless of conditions. At Bortle 3 or below, even a moderate night produces stunning results. StarCast loads the Bortle class for any location you save — so the score you see reflects what's actually achievable there, not just what the atmosphere is doing above it.