ToolComputedCited
When is the moon out of the way this month?
Answer
October 2026 at Cicero: new moon on Oct 10, full moon on Oct 25. 3 of 31 dark nights have no moon above the horizon while it is dark; the most moon-free dark time is 11.7 h on Oct 11.
- 1
65% lit
2.5 h
- 2
54% lit
3.6 h
- 3
43% lit
4.8 h
- 4
32% lit
6.1 h
- 5
22% lit
7.4 h
- 6
13% lit
8.7 h
- 7
7% lit
9.9 h
- 8
2% lit
11.0 h
- 9
0% lit
11.6 h
- 10
0% lit
11.7 h
- 11
3% lit
11.7 h
- 12
7% lit
11.7 h
- 13
13% lit
11.1 h
- 14
20% lit
10.5 h
- 15
28% lit
9.7 h
- 16
36% lit
8.8 h
- 17
46% lit
7.8 h
- 18
55% lit
6.8 h
- 19
65% lit
5.7 h
- 20
74% lit
4.7 h
- 21
82% lit
3.5 h
- 22
89% lit
2.5 h
- 23
95% lit
1.3 h
- 24
99% lit
0.1 h
- 25
100% lit
0.0 h
- 26
98% lit
0.0 h
- 27
94% lit
0.2 h
- 28
87% lit
1.1 h
- 29
79% lit
2.1 h
- 30
68% lit
3.3 h
- 31
57% lit
4.6 h
Each cell is the night that starts on that date. Hours are civil-dark time with the moon below the horizon; the green rule scales with them. Green outline: new moon. Bone outline: full moon.
Worked example
Yellowknife in October 2026: the town has 31 nights with civil darkness and 387.2 hours of civil night in total. The moon is below the horizon for 185.8 of those hours. The new moon falls on Oct 10 in America/Yellowknife time. The full moon falls on Oct 25.
Moon phase and moon-up time are separate. A half-lit moon that sets at dusk leaves the whole night dark. A thin crescent that rises before dawn barely matters. The calendar counts the hours, so both cases show up as they are.
How the calendar is computed
For each night of the month, Glow samples the sun and the moon every 5 minutes from local noon to the next noon. A minute counts as moon-free dark time when the sun is at or below -6 degrees and the moon's center is below the horizon. The calendar cell shows those minutes as hours.
The phase glyph and the percent come from SunCalc's illumination at local midnight: 0% is a new moon, 100% a full moon. New and full moon dates come from the mean lunar phase with the main periodic corrections from Meeus, Astronomical Algorithms, chapter 49. They are accurate to a few minutes and shown in your time zone.
Why the moon matters
SWPC's viewing tips say a full moon diminishes the apparent brightness of the aurora, not the actual brightness. Moonlight brightens the sky background, so faint aurora fades into it. Bright displays still show.
That makes the moon a planning input rather than a veto. The calendar shows how many dark hours each night keeps the moon below the horizon. Nights around the new moon usually have the most. Nights around the full moon usually have the fewest, because a full moon rises near dusk and sets near dawn.
What the calendar leaves out
The calendar says nothing about aurora activity. OVATION looks 30 to 90 minutes ahead, so no one can tell you in advance which night of the month will have a display. Use the calendar to pick the nights with the most dark, moon-free time, then check the live tools on the night.
Terrain can hide a low moon, and cloud can hide a high one. Neither is in the count.
Questions
- Does the full moon ruin the northern lights?
- SWPC says it diminishes the apparent brightness, not the actual brightness. Bright aurora still shows; faint aurora gets harder to see.
- What is moon-free dark time?
- Minutes when the sun is at or below -6 degrees and the moon's center is below the horizon, summed for the night that starts on that date.
- Why can a half moon night be fully dark?
- Phase and moon-up time are different questions. A first quarter moon usually sets around midnight, leaving the rest of the night moonless.
- Which time zone are the new and full moon dates in?
- The one you pick. A new moon at 03:00 UTC falls on the previous evening's date in North American time zones.
- Does the calendar predict aurora activity?
- No. It covers darkness and moon only. Solar activity cannot be forecast that far ahead; OVATION covers the next 30 to 90 minutes.