GoodSeeing Guides
Sun below −18° · next 30 nights

True darkness at Shrewsbury

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 night11.0 h6 Nov
Nights reaching −18°30 / 30Astronomical darkness occurs
Longest window18:40–05:40Moonlight is shown separately in the planner.
Solar geometry, not a clock rule

Hours of astronomical darkness

10 Oct9.0 h0% moon
11 Oct9.0 h2% moon
12 Oct9.3 h6% moon
13 Oct9.7 h12% moon
14 Oct9.7 h18% moon
15 Oct9.7 h26% moon
16 Oct9.7 h35% moon
17 Oct9.7 h44% moon
18 Oct9.7 h53% moon
19 Oct9.7 h63% moon
20 Oct9.7 h72% moon
21 Oct10.0 h80% moon
22 Oct10.0 h88% moon
23 Oct10.0 h94% moon
24 Oct10.0 h98% moon
25 Oct10.3 h100% moon
26 Oct10.3 h99% moon
27 Oct10.3 h96% moon
28 Oct10.3 h90% moon
29 Oct10.3 h82% moon
30 Oct10.3 h72% moon
31 Oct10.7 h61% moon
1 Nov10.7 h49% moon
2 Nov10.7 h38% moon
3 Nov10.7 h27% moon
4 Nov10.7 h18% moon
5 Nov10.7 h10% moon
6 Nov11.0 h5% moon
7 Nov11.0 h2% moon
8 Nov11.0 h0% moon
11.0 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.