Why a clear sky can still look hazy

A night can look cloudless while faint stars and distant objects still appear dim. The atmosphere may have low transparency because haze, dust, smoke, and other tiny particles scatter light. Thin high clouds can also be hard to notice while reducing contrast. Sky transparency forecast — Environment and Climate Change Canada

Transparency and cloud cover are different

A cloud map helps show whether clouds cover the sky, but the absence of thick clouds does not guarantee perfect visibility. Moist air can be accompanied by haze, especially near the horizon. City lights scatter in the lower atmosphere and brighten the background sky. As a result, faint clusters, galaxies, and the Milky Way fade from view sooner than bright stars and planets.

How to check conditions

On the NightSkyCast map, compare the hourly cloud forecast and the night score for your chosen location. Before heading out, check the sky near the horizon, where haze and city glow are more noticeable. If you plan to take photos, try a short test exposure and see how many faint stars appear. When haze is present, moving farther from the city may help, but check the forecast again before you leave.

Check cloud cover for your location on the NightSkyCast map