Sun below −18° · next 30 nights

True darkness at Siding Spring 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 night7.7 h3 Nov

Nights reaching −18°30 / 30Astronomical darkness occurs

Longest window21:00–04:40Moonlight is shown separately in the planner.

Solar geometry, not a clock rule

Hours of astronomical darkness

3 Nov7.7 h32% moon

4 Nov7.7 h22% moon

5 Nov7.7 h14% moon

6 Nov7.3 h7% moon

7 Nov7.3 h3% moon

8 Nov7.3 h1% moon

9 Nov7.3 h0% moon

10 Nov7.3 h2% moon

11 Nov7.3 h5% moon

12 Nov7.3 h10% moon

13 Nov7.3 h17% moon

14 Nov7.3 h24% moon

15 Nov7.3 h33% moon

16 Nov7.3 h42% moon

17 Nov7.3 h52% moon

18 Nov7.3 h62% moon

19 Nov7.3 h71% moon

20 Nov7.3 h80% moon

21 Nov7.3 h88% moon

22 Nov7.3 h94% moon

23 Nov6.7 h98% moon

24 Nov6.7 h100% moon

25 Nov6.7 h99% moon

26 Nov6.7 h95% moon

27 Nov6.7 h89% moon

28 Nov6.7 h80% moon

29 Nov6.7 h70% moon

30 Nov6.7 h59% moon

1 Dec6.7 h48% moon

2 Dec6.7 h37% moon

7.7 hours

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

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−18°

Astronomical darkness

Track true darkness, including polar twilight.