Starcast
Night Sky Forecasts for Astrophotographers

Find out if the stars are worth chasing tonight.

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How Starcast Scores the Sky ↓

Starcast builds a sky quality score from six variables, then applies a target-specific modifier based on what you're actually trying to shoot. Bortle class is estimated from your distance to major light pollution centers.

Cloud Cover
The dominant variable. Even thin cloud blocks faint objects. Below 10% is ideal; above 50% is a serious penalty.
Moon Phase & Illumination
A full moon raises the sky background enough to wash out Milky Way and DSOs entirely. Penalised up to 18 points.
Bortle Class
Estimated from proximity to city cores. Bortle 1–3 adds no penalty; Bortle 7+ can remove 12+ points from the score.
Humidity & Visibility
Atmospheric moisture scatters light and reduces contrast. Low humidity and high visibility are critical for faint targets.
75–100 — Pristine. Rare. Near-perfect conditions.
55–74 — Excellent. Serious astrophotography possible. Go.
35–54 — Good. Wide field and planetary work well.
0–34 — Poor. Limited or no opportunity.

Bortle class is derived from the Falchi et al. (2016) World Atlas of Artificial Night Sky Brightness — a globally calibrated dataset based on VIIRS satellite data and 35,000 SQM ground readings. doi:10.5880/GFZ.1.4.2016.001 · CC BY-NC 4.0

What the Metrics Mean ↓

Milky Way Visibility Guide →


Cloud Cover
The percentage of sky obscured by cloud at shooting time. Even thin, wispy cloud scatters starlight — anything above 30% degrades contrast. Below 10% is the sweet spot for Milky Way and deep sky work.
Bortle Scale
A 1–9 scale of sky brightness from light pollution. Bortle 1 is pristine dark sky; Bortle 9 is inner-city. Estimated here from your distance to major urban centers. At Bortle 7+, the Milky Way core is barely visible to the naked eye.
Moon Illumination
How much of the moon's face is lit. A full moon (100%) raises the entire sky background enough to wash out faint nebulae and the Milky Way. Below 15% is ideal. The rise and set times tell you exactly when dark sky begins and ends.
Visibility
Horizontal visibility in km — a proxy for aerosols, smoke, and particulates in the air. High visibility means clean air and better contrast for faint targets. Below 10km indicates haze that reduces star brightness and sharpness.
Atmospheric Seeing
How steady the air is — thermal turbulence makes stars shimmer and planetary detail blur. Estimated from wind shear between surface and 80m altitude. Poor seeing hurts planetary and lunar work most; wide-field astrophotography is largely immune.
Dew Point Spread
The °C gap between air temperature and dew point. When this narrows below 2°C, moisture condenses on cold lens elements and fogs your optics mid-session. A dew heater eliminates this risk. Above 7°C is safe for unprotected glass.