Hämeenlinna · April 2027
Northern lights in Hämeenlinna in April 2027
Answer
April against the rest of the year
April cloud at Hämeenlinna averages 67% in NASA POWER's 2001 to 2020 record, 5 points clearer than its yearly mean. May is Hämeenlinna's clearest month at 62%. By civil night times clear sky, April scores 2.5 hours at Hämeenlinna, 6th of 12. Lahti, 65 km away, averages the same 67%.
Civil night at Hämeenlinna starts April at 9 h and reaches 5 h 50 min by April 30, 3.2 hours shorter. The 10 PM to 2 AM window is fully dark on 23 of 30 nights. True astronomical darkness, the sun 18 degrees down, lasts 1.4 hours on the 15th.
April night by night
April opens toward a new moon on Apr 7, with full moon on Apr 21, in Europe/Helsinki dates. Hämeenlinna gets 124 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: Apr 1 (4 h), Apr 2 (4 h), Apr 3 (4 h).
- 1
25% lit
9.0 h
- 2
17% lit
8.9 h
- 3
10% lit
8.8 h
- 4
5% lit
8.7 h
- 5
1% lit
8.6 h
- 6
0% lit
8.5 h
- 7
1% lit
7.8 h
- 8
4% lit
6.0 h
- 9
10% lit
4.2 h
- 10
18% lit
2.4 h
- 11
27% lit
1.1 h
- 12
38% lit
0.5 h
- 13
49% lit
0.3 h
- 14
61% lit
0.1 h
- 15
71% lit
0.1 h
- 16
81% lit
0.0 h
- 17
89% lit
0.0 h
- 18
95% lit
0.0 h
- 19
99% lit
0.0 h
- 20
100% lit
0.0 h
- 21
99% lit
0.9 h
- 22
96% lit
2.6 h
- 23
91% lit
4.2 h
- 24
84% lit
5.3 h
- 25
77% lit
5.9 h
- 26
68% lit
6.0 h
- 27
59% lit
6.0 h
- 28
50% lit
6.0 h
- 29
40% lit
5.9 h
- 30
31% lit
5.8 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 Aprils
Hämeenlinna needs Kp 4 for the average oval edge to sit overhead. 251 of the 900 April days from 1996 to 2025 (28%) reached it in the GFZ Potsdam record, 4th of 12 months; storm days with Kp 5 or more made up 12%. Hämeenlinna sits at 58.6 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 4, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.
April across Finland
Hämeenlinna ranks 5th in Finland for civil night on April 15, behind Helsinki at 7.7 hours. Coming from March (10.7 hours at Hämeenlinna), April loses darkness, and May brings shorter nights (4.0 hours on the 15th).
Darkness and moon, every night
| Night | Civil | Astronomical | Moon-free dark | Moon-free, 10 PM to 2 AM | Moon lit |
|---|---|---|---|---|---|
| Thu Apr 1 | 9 h | 4 h 51 min | 9 h | 4 h | 25% |
| Fri Apr 2 | 8 h 54 min | 4 h 41 min | 8 h 54 min | 4 h | 17% |
| Sat Apr 3 | 8 h 47 min | 4 h 31 min | 8 h 47 min | 4 h | 10% |
| Sun Apr 4 | 8 h 41 min | 4 h 20 min | 8 h 41 min | 4 h | 5% |
| Mon Apr 5 | 8 h 35 min | 4 h 9 min | 8 h 35 min | 4 h | 1% |
| Tue Apr 6 | 8 h 29 min | 3 h 58 min | 8 h 29 min | 4 h | 0% |
| Wed Apr 7 | 8 h 23 min | 3 h 46 min | 7 h 50 min | 4 h | 1% |
| Thu Apr 8 | 8 h 16 min | 3 h 34 min | 6 h 3 min | 2 h 32 min | 4% |
| Fri Apr 9 | 8 h 10 min | 3 h 21 min | 4 h 12 min | 44 min | 10% |
| Sat Apr 10 | 8 h 4 min | 3 h 7 min | 2 h 26 min | 0 min | 18% |
| Sun Apr 11 | 7 h 57 min | 2 h 52 min | 1 h 9 min | 0 min | 27% |
| Mon Apr 12 | 7 h 51 min | 2 h 35 min | 32 min | 0 min | 38% |
| Tue Apr 13 | 7 h 44 min | 2 h 17 min | 16 min | 0 min | 49% |
| Wed Apr 14 | 7 h 38 min | 1 h 57 min | 8 min | 0 min | 61% |
| Thu Apr 15 | 7 h 32 min | 1 h 32 min | 3 min | 0 min | 71% |
| Fri Apr 16 | 7 h 25 min | 57 min | 0 min | 0 min | 81% |
| Sat Apr 17 | 7 h 18 min | 0 min | 0 min | 0 min | 89% |
| Sun Apr 18 | 7 h 12 min | 0 min | 0 min | 0 min | 95% |
| Mon Apr 19 | 7 h 5 min | 0 min | 0 min | 0 min | 99% |
| Tue Apr 20 | 6 h 59 min | 0 min | 0 min | 0 min | 100% |
| Wed Apr 21 | 6 h 52 min | 0 min | 55 min | 50 min | 99% |
| Thu Apr 22 | 6 h 45 min | 0 min | 2 h 35 min | 2 h 33 min | 96% |
| Fri Apr 23 | 6 h 39 min | 0 min | 4 h 9 min | 3 h 59 min | 91% |
| Sat Apr 24 | 6 h 32 min | 0 min | 5 h 21 min | 3 h 56 min | 84% |
| Sun Apr 25 | 6 h 25 min | 0 min | 5 h 53 min | 3 h 53 min | 77% |
| Mon Apr 26 | 6 h 18 min | 0 min | 6 h 1 min | 3 h 50 min | 68% |
| Tue Apr 27 | 6 h 11 min | 0 min | 6 h 2 min | 3 h 46 min | 59% |
| Wed Apr 28 | 6 h 4 min | 0 min | 6 h | 3 h 43 min | 50% |
| Thu Apr 29 | 5 h 57 min | 0 min | 5 h 56 min | 3 h 40 min | 40% |
| Fri Apr 30 | 5 h 50 min | 0 min | 5 h 50 min | 3 h 36 min | 31% |
Questions
- Can you see the northern lights in Hämeenlinna in April?
- On dark, clear nights with enough activity. 30 of 30 nights at Hämeenlinna have civil darkness, and 28% of past April days reached Kp 4.
- How dark is Hämeenlinna in April?
- Hämeenlinna averages 7.5 hours of civil night a night in April 2027, from 9 h on the 1st to 5 h 50 min on the last night.
- How cloudy is Hämeenlinna in April?
- NASA POWER's 2001 to 2020 climatology gives Hämeenlinna's 1 degree cell 67% mean cloud in April, against 72% for the whole year. It is an all-hours average, not a forecast.
- What is the best night in April 2027 for aurora in Hämeenlinna?
- By darkness and moon alone, Apr 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Hämeenlinna. Activity on that date will only be known hours ahead.
- Is April or May better in Hämeenlinna?
- By civil night times the clear share, April scores 2.5 hours at Hämeenlinna and May 1.5. April 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.