Sun below −18° · next 30 nights

True darkness at Fairbanks

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 night12.3 h22 Nov

Nights reaching −18°30 / 30Astronomical darkness occurs

Longest window18:40–07:00Moonlight is shown separately in the planner.

Solar geometry, not a clock rule

Hours of astronomical darkness

2 Nov10.7 h34% moon

3 Nov10.7 h23% moon

4 Nov10.7 h15% moon

5 Nov11.0 h8% moon

6 Nov11.0 h3% moon

7 Nov11.0 h1% moon

8 Nov11.0 h0% moon

9 Nov11.0 h2% moon

10 Nov11.3 h5% moon

11 Nov11.3 h9% moon

12 Nov11.3 h15% moon

13 Nov11.7 h23% moon

14 Nov11.7 h31% moon

15 Nov11.7 h40% moon

16 Nov11.7 h50% moon

17 Nov11.7 h60% moon

18 Nov11.7 h70% moon

19 Nov12.0 h79% moon

20 Nov12.0 h87% moon

21 Nov12.0 h93% moon

22 Nov12.3 h98% moon

23 Nov12.3 h100% moon

24 Nov12.3 h99% moon

25 Nov12.3 h96% moon

26 Nov12.3 h90% moon

27 Nov12.3 h82% moon

28 Nov12.3 h72% moon

29 Nov12.3 h61% moon

30 Nov12.3 h50% moon

1 Dec12.3 h39% moon

12.3 hours

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

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Find the longest uninterrupted dark windows.

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See when the galactic core clears the horizon after dark.

−18°

Astronomical darkness

Track true darkness, including polar twilight.