Can you see the northern lights in Viljandi in May?

On dark, clear nights with enough activity. 31 of 31 nights at Viljandi have civil darkness, and 4% of past May days reached Kp 6.

How dark is Viljandi in May?

Viljandi averages 5.0 hours of civil night a night in May 2027, from 6 h 27 min on the 1st to 3 h 40 min on the last night.

How cloudy is Viljandi in May?

NASA POWER's 2001 to 2020 climatology gives Viljandi's 1 degree cell 56% mean cloud in May, against 71% for the whole year. It is an all-hours average, not a forecast.

What is the best night in May 2027 for aurora in Viljandi?

By darkness and moon alone, May 1, with 3 h 59 min of moon-free darkness inside 10 PM to 2 AM at Viljandi. Activity on that date will only be known hours ahead.

Is May or June better in Viljandi?

By civil night times the clear share, May scores 2.2 hours at Viljandi and June 1.0. May comes out ahead.

Viljandi · May 2027

Northern lights in Viljandi in May 2027

Answer

May gives Viljandi 5.1 hours of civil night on the 15th, the 10th darkest of its 12 months, under 56% mean cloud. 4% of May days since 1996 reached Kp 6, enough for the oval edge to reach Viljandi.

5.0 h

civil night, average night

SunCalc for 58.36, 25.59; NASA POWER; GFZ Kp

May against the rest of the year

2.4

2.9

3.5

3.1

2.2

1.0

1.5

2.6

3.1

2.3

2.2

May cloud at Viljandi averages 56% in NASA POWER's 2001 to 2020 record, 15 points clearer than its yearly mean. No month at Viljandi is clearer. By civil night times clear sky, May scores 2.2 hours at Viljandi, 9th of 12. Tallinn, 129 km away, averages 54%, clearer by 2 points.

Civil night at Viljandi starts May at 6 h 27 min and reaches 3 h 40 min by May 31, 2.8 hours shorter. The 10 PM to 2 AM window is fully dark on 1 of 31 nights. The sun never reaches 18 degrees down, so Viljandi gets no astronomical night in May.

May night by night

May opens toward a new moon on May 6, with full moon on May 20, in Europe/Tallinn dates. Viljandi gets 82 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: May 1 (3 h 59 min), May 2 (3 h 56 min), May 3 (3 h 53 min).

1
22% lit
6.1 h
2
15% lit
6.1 h
3
8% lit
6.2 h
4
3% lit
6.2 h
5
1% lit
6.0 h
6
0% lit
6.0 h
New
7
3% lit
4.3 h
8
8% lit
3.0 h
9
15% lit
2.0 h
10
25% lit
1.5 h
11
35% lit
1.1 h
12
46% lit
0.9 h
13
58% lit
0.8 h
14
69% lit
0.7 h
15
78% lit
0.6 h
16
86% lit
0.4 h
17
93% lit
0.3 h
18
97% lit
0.1 h
19
99% lit
0.0 h
20
100% lit
0.1 h
Full
21
98% lit
1.2 h
22
94% lit
2.0 h
23
89% lit
2.5 h
24
82% lit
2.8 h
25
75% lit
2.9 h
26
66% lit
3.0 h
27
57% lit
3.0 h
28
47% lit
3.0 h
29
38% lit
3.0 h
30
28% lit
3.0 h
31
19% lit
3.1 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 Mays

Viljandi needs Kp 6 for the average oval edge to sit overhead. 39 of the 930 May days from 1996 to 2025 (4%) reached it in the GFZ Potsdam record, 4th of 12 months; storm days with Kp 5 or more made up 10%. Viljandi sits at 55.9 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.

May across Estonia

No month-page town in Estonia has more civil night on May 15 than Viljandi; the national median is 4.9 hours. Coming from April (8.0 hours at Viljandi), May loses darkness, and June brings shorter nights (2.8 hours on the 15th).

Civil night on May 15 and May cloud, month-page towns in Estonia
Town	Civil night	Cloud
Viljandi	5.1 h	56%
Tallinn	4.7 h	54%

Darkness and moon, every night

Viljandi, May 2027: each night from local noon to the next noon
Night	Civil	Moon-free dark	Moon-free, 10 PM to 2 AM	Moon lit
Sat May 1	6 h 27 min	6 h 7 min	3 h 59 min	22%
Sun May 2	6 h 21 min	6 h 8 min	3 h 56 min	15%
Mon May 3	6 h 15 min	6 h 9 min	3 h 53 min	8%
Tue May 4	6 h 9 min	6 h 9 min	3 h 51 min	3%
Wed May 5	6 h 3 min	6 h 3 min	3 h 48 min	1%
Thu May 6	5 h 58 min	5 h 58 min	3 h 45 min	0%
Fri May 7	5 h 52 min	4 h 21 min	2 h 11 min	3%
Sat May 8	5 h 46 min	2 h 57 min	50 min	8%
Sun May 9	5 h 40 min	2 h	0 min	15%
Mon May 10	5 h 34 min	1 h 28 min	0 min	25%
Tue May 11	5 h 29 min	1 h 9 min	0 min	35%
Wed May 12	5 h 23 min	56 min	0 min	46%
Thu May 13	5 h 17 min	47 min	0 min	58%
Fri May 14	5 h 11 min	40 min	0 min	69%
Sat May 15	5 h 5 min	33 min	0 min	78%
Sun May 16	5 h	26 min	0 min	86%
Mon May 17	4 h 54 min	17 min	0 min	93%
Tue May 18	4 h 48 min	7 min	0 min	97%
Wed May 19	4 h 43 min	0 min	0 min	99%
Thu May 20	4 h 37 min	3 min	3 min	100%
Fri May 21	4 h 32 min	1 h 14 min	1 h 14 min	98%
Sat May 22	4 h 26 min	2 h 3 min	2 h 3 min	94%
Sun May 23	4 h 21 min	2 h 31 min	2 h 31 min	89%
Mon May 24	4 h 15 min	2 h 46 min	2 h 46 min	82%
Tue May 25	4 h 10 min	2 h 53 min	2 h 51 min	75%
Wed May 26	4 h 5 min	2 h 57 min	2 h 48 min	66%
Thu May 27	4 h	2 h 59 min	2 h 45 min	57%
Fri May 28	3 h 54 min	3 h	2 h 42 min	47%
Sat May 29	3 h 49 min	3 h 1 min	2 h 40 min	38%
Sun May 30	3 h 44 min	3 h 2 min	2 h 37 min	28%
Mon May 31	3 h 40 min	3 h 4 min	2 h 35 min	19%

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

Questions

Can you see the northern lights in Viljandi in May?: On dark, clear nights with enough activity. 31 of 31 nights at Viljandi have civil darkness, and 4% of past May days reached Kp 6.
How dark is Viljandi in May?: Viljandi averages 5.0 hours of civil night a night in May 2027, from 6 h 27 min on the 1st to 3 h 40 min on the last night.
How cloudy is Viljandi in May?: NASA POWER's 2001 to 2020 climatology gives Viljandi's 1 degree cell 56% mean cloud in May, against 71% for the whole year. It is an all-hours average, not a forecast.
What is the best night in May 2027 for aurora in Viljandi?: By darkness and moon alone, May 1, with 3 h 59 min of moon-free darkness inside 10 PM to 2 AM at Viljandi. Activity on that date will only be known hours ahead.
Is May or June better in Viljandi?: By civil night times the clear share, May scores 2.2 hours at Viljandi and June 1.0. May 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.