Can you see the northern lights in Slagelse in August?

On dark, clear nights with enough activity. 31 of 31 nights at Slagelse have civil darkness, and 3% of past August days reached Kp 6.

How dark is Slagelse in August?

Slagelse averages 7.5 hours of civil night a night in August 2027, from 6 h 19 min on the 1st to 8 h 43 min on the last night.

How cloudy is Slagelse in August?

NASA POWER's 2001 to 2020 climatology gives Slagelse's 1 degree cell 63% mean cloud in August, against 68% for the whole year. It is an all-hours average, not a forecast.

What is the best night in August 2027 for aurora in Slagelse?

By darkness and moon alone, Aug 6, with 4 h of moon-free darkness inside 10 PM to 2 AM at Slagelse. Activity on that date will only be known hours ahead.

Is August or September better in Slagelse?

By civil night times the clear share, August scores 2.8 hours at Slagelse and September 3.8. September comes out ahead.

Slagelse · August 2027

Northern lights in Slagelse in August 2027

Answer

August gives Slagelse 7.5 hours of civil night on the 15th, the 9th darkest of its 12 months, under 63% mean cloud. 3% of August days since 1996 reached Kp 6, enough for the oval edge to reach Slagelse.

7.5 h

civil night, average night

SunCalc for 55.40, 11.35; NASA POWER; GFZ Kp

August against the rest of the year

2.9

2.8

3.5

3.6

2.5

1.7

1.9

2.8

3.8

3.9

3.4

3.2

August cloud at Slagelse averages 63% in NASA POWER's 2001 to 2020 record, 5 points clearer than its yearly mean. April is Slagelse's clearest month at 57%. By civil night times clear sky, August scores 2.8 hours at Slagelse, 9th of 12. Odense, 61 km away, averages the same 63%.

Civil night at Slagelse starts August at 6 h 19 min and reaches 8 h 43 min by August 31 as the nights lengthen by 2.4 hours. The 10 PM to 2 AM window is fully dark on 26 of 31 nights. True astronomical darkness, the sun 18 degrees down, lasts 2.9 hours on the 15th.

August night by night

August opens toward a new moon on Aug 2 and Aug 31, with full moon on Aug 17, in Europe/Copenhagen dates. Slagelse gets 117 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: Aug 6 (4 h), Aug 28 (4 h), Aug 29 (4 h).

1
0% lit
6.3 h
2
0% lit
6.4 h
New
3
3% lit
6.5 h
4
9% lit
6.5 h
5
17% lit
6.6 h
6
26% lit
6.7 h
7
37% lit
6.6 h
8
47% lit
6.4 h
9
57% lit
6.1 h
10
67% lit
5.7 h
11
76% lit
5.0 h
12
84% lit
4.1 h
13
90% lit
3.0 h
14
95% lit
1.8 h
15
98% lit
0.5 h
16
100% lit
0.0 h
17
100% lit
0.0 h
Full
18
98% lit
0.0 h
19
94% lit
0.0 h
20
88% lit
0.0 h
21
81% lit
0.0 h
22
72% lit
0.0 h
23
63% lit
0.3 h
24
52% lit
0.8 h
25
41% lit
1.4 h
26
30% lit
2.5 h
27
20% lit
3.8 h
28
11% lit
5.4 h
29
5% lit
7.1 h
30
1% lit
8.6 h
31
0% lit
8.7 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 Augusts

Slagelse needs Kp 6 for the average oval edge to sit overhead. 28 of the 930 August days from 1996 to 2025 (3%) reached it in the GFZ Potsdam record, 8th of 12 months; storm days with Kp 5 or more made up 11%. Slagelse sits at 55.3 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 6, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.

August across Denmark

No month-page town in Denmark has more civil night on August 15 than Slagelse; the national median is 7.4 hours. Coming from July (5.2 hours at Slagelse), August adds darkness, and the nights keep growing into September (9.9 hours on the 15th).

Civil night on August 15 and August cloud, month-page towns in Denmark
Town	Civil night	Cloud
Slagelse	7.5 h	63%
Odense	7.5 h	63%
Copenhagen	7.4 h	65%
Århus	7.3 h	66%
Aalborg	7.2 h	67%

Darkness and moon, every night

Slagelse, August 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
Sun Aug 1	6 h 19 min	0 min	6 h 19 min	3 h 48 min	0%
Mon Aug 2	6 h 24 min	0 min	6 h 24 min	3 h 51 min	0%
Tue Aug 3	6 h 29 min	0 min	6 h 29 min	3 h 53 min	3%
Wed Aug 4	6 h 33 min	0 min	6 h 33 min	3 h 56 min	9%
Thu Aug 5	6 h 38 min	0 min	6 h 38 min	3 h 58 min	17%
Fri Aug 6	6 h 43 min	0 min	6 h 43 min	4 h	26%
Sat Aug 7	6 h 47 min	0 min	6 h 37 min	3 h 52 min	37%
Sun Aug 8	6 h 52 min	41 min	6 h 25 min	3 h 38 min	47%
Mon Aug 9	6 h 57 min	1 h 13 min	6 h 7 min	3 h 19 min	57%
Tue Aug 10	7 h 2 min	1 h 35 min	5 h 41 min	2 h 50 min	67%
Wed Aug 11	7 h 7 min	1 h 53 min	5 h 2 min	2 h 8 min	76%
Thu Aug 12	7 h 11 min	2 h 9 min	4 h 7 min	1 h 11 min	84%
Fri Aug 13	7 h 16 min	2 h 23 min	2 h 59 min	2 min	90%
Sat Aug 14	7 h 21 min	2 h 36 min	1 h 46 min	0 min	95%
Sun Aug 15	7 h 26 min	2 h 48 min	30 min	0 min	98%
Mon Aug 16	7 h 31 min	3 h	0 min	0 min	100%
Tue Aug 17	7 h 35 min	3 h 11 min	0 min	0 min	100%
Wed Aug 18	7 h 40 min	3 h 21 min	0 min	0 min	98%
Thu Aug 19	7 h 45 min	3 h 31 min	0 min	0 min	94%
Fri Aug 20	7 h 50 min	3 h 40 min	0 min	0 min	88%
Sat Aug 21	7 h 55 min	3 h 50 min	0 min	0 min	81%
Sun Aug 22	8 h	3 h 59 min	2 min	0 min	72%
Mon Aug 23	8 h 4 min	4 h 7 min	21 min	0 min	63%
Tue Aug 24	8 h 9 min	4 h 16 min	47 min	0 min	52%
Wed Aug 25	8 h 14 min	4 h 24 min	1 h 27 min	37 min	41%
Thu Aug 26	8 h 19 min	4 h 32 min	2 h 27 min	1 h 34 min	30%
Fri Aug 27	8 h 24 min	4 h 40 min	3 h 49 min	2 h 53 min	20%
Sat Aug 28	8 h 29 min	4 h 48 min	5 h 26 min	4 h	11%
Sun Aug 29	8 h 33 min	4 h 55 min	7 h 8 min	4 h	5%
Mon Aug 30	8 h 38 min	5 h 3 min	8 h 38 min	4 h	1%
Tue Aug 31	8 h 43 min	5 h 10 min	8 h 43 min	4 h	0%

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

Questions

Can you see the northern lights in Slagelse in August?: On dark, clear nights with enough activity. 31 of 31 nights at Slagelse have civil darkness, and 3% of past August days reached Kp 6.
How dark is Slagelse in August?: Slagelse averages 7.5 hours of civil night a night in August 2027, from 6 h 19 min on the 1st to 8 h 43 min on the last night.
How cloudy is Slagelse in August?: NASA POWER's 2001 to 2020 climatology gives Slagelse's 1 degree cell 63% mean cloud in August, against 68% for the whole year. It is an all-hours average, not a forecast.
What is the best night in August 2027 for aurora in Slagelse?: By darkness and moon alone, Aug 6, with 4 h of moon-free darkness inside 10 PM to 2 AM at Slagelse. Activity on that date will only be known hours ahead.
Is August or September better in Slagelse?: By civil night times the clear share, August scores 2.8 hours at Slagelse and September 3.8. September 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.