Longyearbyen · September 2027
Northern lights in Longyearbyen in September 2027
Answer
September against the rest of the year
September cloud at Longyearbyen averages 83% in NASA POWER's 2001 to 2020 record, 7 points cloudier than its yearly mean. April is Longyearbyen's clearest month at 67%. By civil night times clear sky, September scores 0.9 hours at Longyearbyen, 7th of 12. Alta, 945 km away, averages 81%, clearer by 2 points.
Civil night at Longyearbyen starts September at 0 min and reaches 9 h 39 min by September 30 as the nights lengthen by 9.7 hours. 8 Longyearbyen nights this month have no civil darkness at all. The 10 PM to 2 AM window is fully dark on 14 of 30 nights. The sun never reaches 18 degrees down, so Longyearbyen gets no astronomical night in September.
September night by night
Full moon comes first, on Sep 16, then the new moon on Sep 30, in Arctic/Longyearbyen dates. Longyearbyen gets 47 hours of civil night with the moon below the horizon across the month. The best of them for moon-free darkness inside 10 PM to 2 AM: Sep 27 (4 h), Sep 28 (4 h), Sep 29 (4 h).
- 1
2% lit
no night
- 2
7% lit
no night
- 3
14% lit
no night
- 4
22% lit
no night
- 5
32% lit
no night
- 6
42% lit
no night
- 7
52% lit
no night
- 8
61% lit
no night
- 9
70% lit
1.3 h
- 10
79% lit
2.4 h
- 11
86% lit
3.1 h
- 12
92% lit
3.6 h
- 13
96% lit
2.0 h
- 14
99% lit
0.0 h
- 15
100% lit
0.0 h
- 16
99% lit
0.0 h
- 17
96% lit
0.0 h
- 18
91% lit
0.0 h
- 19
85% lit
0.0 h
- 20
76% lit
0.0 h
- 21
67% lit
0.0 h
- 22
56% lit
0.0 h
- 23
45% lit
0.0 h
- 24
33% lit
0.0 h
- 25
23% lit
0.0 h
- 26
14% lit
0.0 h
- 27
7% lit
6.4 h
- 28
2% lit
9.1 h
- 29
0% lit
9.4 h
- 30
1% lit
9.7 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.
Activity in past Septembers
Quiet activity already puts the oval edge over Longyearbyen, so storm days matter more: 126 of the 900 September days from 1996 to 2025 (14%) reached Kp 5, one of the three most active months for that level. Longyearbyen sits at 75.3 degrees geomagnetic, poleward of SWPC's 60 to 75 degree band. The quiet oval can lie south of the town, so aurora often shows low in the southern sky, and storms push the oval farther south.
September across Svalbard and Jan Mayen
Coming from August (0.0 hours at Longyearbyen), September adds darkness, and the nights keep growing into October (13.4 hours on the 15th). The September equinox falls on September 23, 07:56 Longyearbyen time, inside the weeks SWPC links with larger storms.
Darkness and moon, every night
| Night | Civil | Astronomical | Moon-free dark | Moon-free, 10 PM to 2 AM | Moon lit |
|---|---|---|---|---|---|
| Wed Sep 1 | 0 min | 0 min | 0 min | 0 min | 2% |
| Thu Sep 2 | 0 min | 0 min | 0 min | 0 min | 7% |
| Fri Sep 3 | 0 min | 0 min | 0 min | 0 min | 14% |
| Sat Sep 4 | 0 min | 0 min | 0 min | 0 min | 22% |
| Sun Sep 5 | 0 min | 0 min | 0 min | 0 min | 32% |
| Mon Sep 6 | 0 min | 0 min | 0 min | 0 min | 42% |
| Tue Sep 7 | 0 min | 0 min | 0 min | 0 min | 52% |
| Wed Sep 8 | 0 min | 0 min | 0 min | 0 min | 61% |
| Thu Sep 9 | 1 h 19 min | 0 min | 1 h 19 min | 1 h 19 min | 70% |
| Fri Sep 10 | 2 h 21 min | 0 min | 2 h 21 min | 2 h 15 min | 79% |
| Sat Sep 11 | 3 h 4 min | 0 min | 3 h 4 min | 2 h 37 min | 86% |
| Sun Sep 12 | 3 h 39 min | 0 min | 3 h 39 min | 2 h 55 min | 92% |
| Mon Sep 13 | 4 h 9 min | 0 min | 2 h 1 min | 1 h 2 min | 96% |
| Tue Sep 14 | 4 h 37 min | 0 min | 0 min | 0 min | 99% |
| Wed Sep 15 | 5 h 2 min | 0 min | 0 min | 0 min | 100% |
| Thu Sep 16 | 5 h 25 min | 0 min | 0 min | 0 min | 99% |
| Fri Sep 17 | 5 h 48 min | 0 min | 0 min | 0 min | 96% |
| Sat Sep 18 | 6 h 9 min | 0 min | 0 min | 0 min | 91% |
| Sun Sep 19 | 6 h 29 min | 0 min | 0 min | 0 min | 85% |
| Mon Sep 20 | 6 h 49 min | 0 min | 0 min | 0 min | 76% |
| Tue Sep 21 | 7 h 8 min | 0 min | 0 min | 0 min | 67% |
| Wed Sep 22 | 7 h 26 min | 0 min | 0 min | 0 min | 56% |
| Thu Sep 23 | 7 h 44 min | 0 min | 0 min | 0 min | 45% |
| Fri Sep 24 | 8 h 1 min | 0 min | 0 min | 0 min | 33% |
| Sat Sep 25 | 8 h 18 min | 0 min | 0 min | 0 min | 23% |
| Sun Sep 26 | 8 h 35 min | 0 min | 0 min | 0 min | 14% |
| Mon Sep 27 | 8 h 51 min | 0 min | 6 h 22 min | 4 h | 7% |
| Tue Sep 28 | 9 h 7 min | 0 min | 9 h 7 min | 4 h | 2% |
| Wed Sep 29 | 9 h 23 min | 0 min | 9 h 23 min | 4 h | 0% |
| Thu Sep 30 | 9 h 39 min | 0 min | 9 h 39 min | 4 h | 1% |
Questions
- Can you see the northern lights in Longyearbyen in September?
- On dark, clear nights with enough activity. 22 of 30 nights at Longyearbyen have civil darkness, and 14% of past September days reached Kp 5.
- How dark is Longyearbyen in September?
- Longyearbyen averages 4.6 hours of civil night a night in September 2027, from 0 min on the 1st to 9 h 39 min on the last night.
- How cloudy is Longyearbyen in September?
- NASA POWER's 2001 to 2020 climatology gives Longyearbyen's 1 degree cell 83% mean cloud in September, against 76% for the whole year. It is an all-hours average, not a forecast.
- What is the best night in September 2027 for aurora in Longyearbyen?
- By darkness and moon alone, Sep 27, with 4 h of moon-free darkness inside 10 PM to 2 AM at Longyearbyen. Activity on that date will only be known hours ahead.
- Is September or October better in Longyearbyen?
- By civil night times the clear share, September scores 0.9 hours at Longyearbyen and October 2.8. October comes out ahead.
Sources and verification
- SunCalchttps://github.com/mourner/suncalc
- NASA POWER climatologyhttps://power.larc.nasa.gov/docs/services/api/temporal/climatology/
- GFZ Potsdam Kp indexhttps://kp.gfz.de/en/data
- NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora
Quoted figures last checked against their sources on 2026-09-30; next review 2026-12-31. Computed figures come from SunCalc and the IGRF-14 dipole as described in the methodology. Every quote is listed in the sources ledger.