Sun below −18° · next 30 nights

True darkness at Swift Current

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 h7 Nov

Nights reaching −18°30 / 30Astronomical darkness occurs

Longest window19:40–06:40Moonlight is shown separately in the planner.

Solar geometry, not a clock rule

Hours of astronomical darkness

10 Oct9.3 h1% moon

11 Oct9.7 h3% moon

12 Oct9.7 h8% moon

13 Oct9.7 h13% moon

14 Oct9.7 h21% moon

15 Oct9.7 h29% moon

16 Oct9.7 h37% moon

17 Oct9.7 h47% moon

18 Oct9.7 h56% moon

19 Oct9.7 h66% moon

20 Oct10.0 h74% moon

21 Oct10.0 h83% moon

22 Oct10.0 h90% moon

23 Oct10.0 h95% moon

24 Oct10.3 h99% moon

25 Oct10.3 h100% moon

26 Oct10.3 h98% moon

27 Oct10.3 h95% moon

28 Oct10.3 h88% moon

29 Oct10.3 h80% moon

30 Oct10.3 h69% moon

31 Oct10.7 h58% moon

1 Nov10.7 h46% moon

2 Nov10.7 h35% moon

3 Nov10.7 h25% moon

4 Nov10.7 h16% moon

5 Nov10.7 h9% moon

6 Nov10.7 h4% moon

7 Nov11.0 h1% 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 →

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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.