Can you see the northern lights in Sligo in September?

On dark, clear nights with enough activity. 30 of 30 nights at Sligo have civil darkness, and 14% of past September days reached Kp 5.

How dark is Sligo in September?

Sligo averages 10.0 hours of civil night a night in September 2027, from 8 h 55 min on the 1st to 11 h 5 min on the last night.

How cloudy is Sligo in September?

NASA POWER's 2001 to 2020 climatology gives Sligo's 1 degree cell 80% mean cloud in September, against 81% for the whole year. It is an all-hours average, not a forecast.

What is the best night in September 2027 for aurora in Sligo?

By darkness and moon alone, Sep 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Sligo. Activity on that date will only be known hours ahead.

Is September or October better in Sligo?

By civil night times the clear share, September scores 2.0 hours at Sligo and October 2.6. October comes out ahead.

Sligo · September 2027

Northern lights in Sligo in September 2027

Answer

September gives Sligo 10.0 hours of civil night on the 15th, the 7th darkest of its 12 months, under 80% mean cloud. 14% of September days since 1996 reached Kp 5, enough for the oval edge to reach Sligo.

10.0 h

civil night, average night

SunCalc for 54.27, -8.47; NASA POWER; GFZ Kp

September against the rest of the year

2.3

2.1

2.0

1.5

0.9

0.8

1.3

2.0

2.6

2.5

2.6

September cloud at Sligo averages 80% in NASA POWER's 2001 to 2020 record, close to its yearly mean of 81%. May is Sligo's clearest month at 76%. By civil night times clear sky, September scores 2.0 hours at Sligo, 7th of 12. Belfast, 168 km away, averages 76%, clearer by 4 points.

Civil night at Sligo starts September at 8 h 55 min and reaches 11 h 5 min by September 30 as the nights lengthen by 2.2 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 7.0 hours on the 15th.

September night by night

Full moon comes first, on Sep 16, then the new moon on Sep 30, in Europe/Dublin dates. Sligo gets 152 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 1 (4 h), Sep 2 (4 h), Sep 3 (4 h).

1
2% lit
8.9 h
2
7% lit
9.0 h
3
14% lit
9.1 h
4
23% lit
9.2 h
5
32% lit
8.9 h
6
42% lit
8.5 h
7
52% lit
7.9 h
8
62% lit
7.0 h
9
71% lit
6.0 h
10
79% lit
4.8 h
11
86% lit
3.6 h
12
92% lit
2.3 h
13
96% lit
1.1 h
14
99% lit
0.0 h
15
100% lit
0.0 h
16
99% lit
0.0 h
Full
17
96% lit
0.0 h
18
91% lit
0.0 h
19
84% lit
0.0 h
20
76% lit
0.3 h
21
66% lit
0.9 h
22
55% lit
1.8 h
23
44% lit
3.0 h
24
33% lit
4.5 h
25
23% lit
6.0 h
26
14% lit
7.6 h
27
6% lit
9.2 h
28
2% lit
10.8 h
29
0% lit
11.0 h
30
1% lit
11.1 h
New

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

Sligo needs Kp 5 for the average oval edge to sit overhead. 126 of the 900 September days from 1996 to 2025 (14%) reached it in the GFZ Potsdam record, one of the three most active months for that level; storm days with Kp 5 or more made up 14%. Sligo sits at 57.3 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 5, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.

September across Ireland

Sligo ranks 4th in Ireland for civil night on September 15, behind Dublin at 10.1 hours. Coming from August (7.6 hours at Sligo), September adds darkness, and the nights keep growing into October (12.2 hours on the 15th). The September equinox falls on September 23, 06:56 Sligo time, inside the weeks SWPC links with larger storms.

Civil night on September 15 and September cloud, month-page towns in Ireland
Town	Civil night	Cloud
Dublin	10.1 h	74%
Cork	10.1 h	68%
Limerick	10.1 h	74%
Sligo	10.0 h	80%

Darkness and moon, every night

Sligo, September 2027: each night from local noon to the next noon
Night	Civil	Astronomical	Moon-free dark	Moon-free, 10 PM to 2 AM	Moon lit
Wed Sep 1	8 h 55 min	5 h 34 min	8 h 55 min	4 h	2%
Thu Sep 2	9 h	5 h 41 min	9 h	4 h	7%
Fri Sep 3	9 h 4 min	5 h 47 min	9 h 4 min	4 h	14%
Sat Sep 4	9 h 9 min	5 h 54 min	9 h 9 min	4 h	23%
Sun Sep 5	9 h 13 min	6 h	8 h 56 min	4 h	32%
Mon Sep 6	9 h 18 min	6 h 6 min	8 h 30 min	4 h	42%
Tue Sep 7	9 h 22 min	6 h 12 min	7 h 53 min	3 h 39 min	52%
Wed Sep 8	9 h 27 min	6 h 18 min	7 h 1 min	2 h 46 min	62%
Thu Sep 9	9 h 32 min	6 h 24 min	5 h 58 min	1 h 41 min	71%
Fri Sep 10	9 h 36 min	6 h 30 min	4 h 47 min	28 min	79%
Sat Sep 11	9 h 41 min	6 h 36 min	3 h 34 min	0 min	86%
Sun Sep 12	9 h 45 min	6 h 41 min	2 h 20 min	0 min	92%
Mon Sep 13	9 h 50 min	6 h 47 min	1 h 8 min	0 min	96%
Tue Sep 14	9 h 54 min	6 h 53 min	0 min	0 min	99%
Wed Sep 15	9 h 59 min	6 h 58 min	0 min	0 min	100%
Thu Sep 16	10 h 3 min	7 h 4 min	0 min	0 min	99%
Fri Sep 17	10 h 7 min	7 h 9 min	0 min	0 min	96%
Sat Sep 18	10 h 12 min	7 h 15 min	0 min	0 min	91%
Sun Sep 19	10 h 16 min	7 h 20 min	0 min	0 min	84%
Mon Sep 20	10 h 21 min	7 h 25 min	16 min	0 min	76%
Tue Sep 21	10 h 25 min	7 h 30 min	53 min	0 min	66%
Wed Sep 22	10 h 30 min	7 h 36 min	1 h 47 min	0 min	55%
Thu Sep 23	10 h 34 min	7 h 41 min	2 h 59 min	1 h 9 min	44%
Fri Sep 24	10 h 38 min	7 h 46 min	4 h 27 min	2 h 34 min	33%
Sat Sep 25	10 h 43 min	7 h 51 min	6 h 2 min	4 h	23%
Sun Sep 26	10 h 47 min	7 h 56 min	7 h 38 min	4 h	14%
Mon Sep 27	10 h 52 min	8 h 1 min	9 h 13 min	4 h	6%
Tue Sep 28	10 h 56 min	8 h 6 min	10 h 47 min	4 h	2%
Wed Sep 29	11 h	8 h 11 min	11 h	4 h	0%
Thu Sep 30	11 h 5 min	8 h 15 min	11 h 5 min	4 h	1%

Moon lit: SunCalc illuminated fraction at the middle of the 10 PM to 2 AM window.

Questions

Can you see the northern lights in Sligo in September?: On dark, clear nights with enough activity. 30 of 30 nights at Sligo have civil darkness, and 14% of past September days reached Kp 5.
How dark is Sligo in September?: Sligo averages 10.0 hours of civil night a night in September 2027, from 8 h 55 min on the 1st to 11 h 5 min on the last night.
How cloudy is Sligo in September?: NASA POWER's 2001 to 2020 climatology gives Sligo's 1 degree cell 80% mean cloud in September, against 81% for the whole year. It is an all-hours average, not a forecast.
What is the best night in September 2027 for aurora in Sligo?: By darkness and moon alone, Sep 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Sligo. Activity on that date will only be known hours ahead.
Is September or October better in Sligo?: By civil night times the clear share, September scores 2.0 hours at Sligo and October 2.6. 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.