GoodSeeing Guides
Sun below −18° · next 30 nights

True darkness at Paranal Observatory

Astronomical darkness starts only when the Sun is 18° below the horizon. These bars are calculated for the coordinates, so high-latitude nights correctly show no true darkness when twilight never ends.

Longest night8.7 h10 Oct
Nights reaching −18°30 / 30Astronomical darkness occurs
Longest window21:20–06:00Moonlight is shown separately in the planner.
Solar geometry, not a clock rule

Hours of astronomical darkness

10 Oct8.7 h1% moon
11 Oct8.7 h3% moon
12 Oct8.7 h7% moon
13 Oct8.7 h13% moon
14 Oct8.7 h20% moon
15 Oct8.7 h28% moon
16 Oct8.7 h36% moon
17 Oct8.7 h45% moon
18 Oct8.7 h55% moon
19 Oct8.7 h64% moon
20 Oct8.7 h73% moon
21 Oct8.7 h82% moon
22 Oct8.7 h89% moon
23 Oct8.7 h95% moon
24 Oct8.7 h98% moon
25 Oct8.3 h100% moon
26 Oct8.3 h99% moon
27 Oct8.3 h95% moon
28 Oct8.3 h89% moon
29 Oct8.3 h81% moon
30 Oct8.3 h71% moon
31 Oct8.3 h60% moon
1 Nov8.3 h48% moon
2 Nov8.3 h36% moon
3 Nov8.3 h26% moon
4 Nov8.0 h17% moon
5 Nov8.0 h10% moon
6 Nov8.0 h4% moon
7 Nov8.0 h1% moon
8 Nov8.0 h0% moon
8.7 hours

Use this as the outer boundary for faint-object work. Moon altitude, cloud and transparency will narrow the practical window. Add the Moon →

Keep planning

Same coordinates, different question

Moon

Moonless nights

Find the longest uninterrupted dark windows.

Core

Milky Way

See when the galactic core clears the horizon after dark.

−18°

Astronomical darkness

Track true darkness, including polar twilight.