Astrophotography forecast and planner

Clear skies come first. After that the Moon matters most, because a bright Moon above the horizon lights up the whole sky and washes out faint galaxies and dust. Low humidity, little wind and a site away from city lights all help too.

Every 10 minutes between astronomical dusk and dawn gets a quality value from the forecast cloud cover and the Moon’s brightness while it is above the horizon. The night’s score is the average, reduced for short summer nights and strong wind. The broadband score suits galaxies, clusters and unfiltered imaging. The narrowband score assumes a dual-band or narrowband filter, which blocks most moonlight.

The week or so around new Moon, when the Moon is down or is a thin crescent that sets early. Around first quarter the Moon sets near midnight, so the second half of the night is dark. Around last quarter it rises near midnight, so the evening is dark. The outlook chart shows how many Moon-free hours each night has.

Yes, if you pick the right targets. Emission nebulae such as the Orion, Rosette, North America and Heart nebulae glow in a few narrow wavelengths. A dual-band or narrowband filter lets that light through and blocks most of the moonlight. Bright star clusters, the Moon and the planets also work. Galaxies and reflection nebulae need a dark, moonless sky.

Hourly cloud, humidity and wind forecasts come from Open-Meteo and go out 16 days. Moon phase, moonrise, moonset and darkness times are calculated, so the outlook covers the next four months. You can open any of those nights to see its targets.

It is when the Sun is more than 18° below the horizon and adds no light to the sky. This is the best time for faint deep-sky objects. Near the summer solstice at high latitudes the Sun never gets that low, so the planner uses nautical darkness (12° below) instead.