Not all darkness is equal. After sunset, the sky passes through three twilight phases: civil, nautical, and astronomical. True astrophotography darkness — the kind where the Milky Way comes out — only begins at astronomical darkness, roughly 90 minutes to 2 hours after sunset depending on your latitude and time of year.
The moon is the other variable most people underestimate. A full moon can raise sky brightness by 100 times compared to a moonless night. Moon rise and set times matter as much as moon phase — a 70% moon that sets before astronomical darkness gives you a fully dark window. A 30% moon that rises at midnight cuts your shooting window in half.
The sky quality score above combines cloud cover, transparency, humidity, and moon illumination into a single number. Anything above 65 is worth the drive to a dark site.
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Frequently Asked Questions
Astronomical darkness begins roughly 90 minutes to 2 hours after sunset, when the sun is more than 18 degrees below the horizon. Before that, residual twilight washes out the Milky Way and faint stars. Enter your city above for tonight's exact time. Open Starcast for a full night sky forecast →
Astronomical twilight is when the sun is 12–18 degrees below the horizon — the sky still has scattered light that affects faint-object photography. Astronomical darkness starts when the sun exceeds 18 degrees below the horizon. For serious astrophotography, especially the Milky Way and faint nebulae, you want true astronomical darkness.
A full moon raises sky brightness by roughly 100x compared to a moonless night. Even at 50% illumination, faint targets like the Milky Way core are significantly washed out. For Milky Way photography, aim for moon illumination below 25%. Moon rise and set times matter too — a moon that sets before dark gives you a fully dark window regardless of phase. Read: How moon phase affects astrophotography →
Starcast scores nights 0–100. Above 65 is genuinely good — clear, transparent, and low moon. Above 75 is excellent. Below 40 typically means heavy cloud cover, high humidity, or a bright moon. The score already accounts for your local Bortle class, cloud cover, and moon illumination.
In the Northern Hemisphere, the galactic core is visible from roughly March through October, peaking June through August. New moon windows during those months offer the best conditions. Read: Milky Way visibility guide →
Light pollution is measured on the Bortle scale from 1 (pristine) to 9 (inner city). At Bortle 8–9 the Milky Way is invisible. At Bortle 4–5 the galactic core is clearly visible. Getting to a darker site is often the most impactful thing you can do. Find dark skies near you →