Can you see the northern lights in Casper in May?

On dark, clear nights with enough activity. 31 of 31 nights at Casper have civil darkness, and 1% of past May days reached Kp 8.

How dark is Casper in May?

Casper averages 8.1 hours of civil night a night in May 2027, from 8 h 44 min on the 1st to 7 h 38 min on the last night.

How cloudy is Casper in May?

NASA POWER's 2001 to 2020 climatology gives Casper's 1 degree cell 62% mean cloud in May, against 56% for the whole year. It is an all-hours average, not a forecast.

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

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

Is May or June better in Casper?

By civil night times the clear share, May scores 3.1 hours at Casper and June 4.1. June comes out ahead.

Casper · May 2027

Northern lights in Casper in May 2027

Answer

May gives Casper 8.1 hours of civil night on the 15th, the 10th darkest of its 12 months, under 62% mean cloud. 1% of May days since 1996 reached Kp 8, enough for the oval edge to reach Casper.

8.1 h

civil night, average night

SunCalc for 42.87, -106.31; NASA POWER; GFZ Kp

May against the rest of the year

5.0

3.9

3.7

3.3

3.1

4.1

4.6

5.1

6.2

5.6

5.3

4.7

May cloud at Casper averages 62% in NASA POWER's 2001 to 2020 record, 6 points cloudier than its yearly mean. July is Casper's clearest month at 41%. By civil night times clear sky, May scores 3.1 hours at Casper, 12th of 12. Regina, 853 km away, averages the same 62%.

Civil night at Casper starts May at 8 h 44 min and reaches 7 h 38 min by May 31, 1.1 hours shorter. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 5.2 hours on the 15th.

May night by night

May opens toward a new moon on May 6, with full moon on May 20, in America/Denver dates. Casper gets 128 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 (4 h), May 2 (4 h), May 3 (4 h).

1
19% lit
7.2 h
2
12% lit
7.5 h
3
6% lit
7.9 h
4
2% lit
8.3 h
5
0% lit
8.6 h
6
1% lit
8.2 h
New
7
4% lit
6.9 h
8
10% lit
5.8 h
9
19% lit
4.8 h
10
28% lit
4.0 h
11
39% lit
3.5 h
12
51% lit
3.0 h
13
62% lit
2.5 h
14
72% lit
2.1 h
15
81% lit
1.8 h
16
89% lit
1.4 h
17
95% lit
0.9 h
18
98% lit
0.4 h
19
100% lit
0.0 h
20
99% lit
0.3 h
Full
21
97% lit
1.3 h
22
92% lit
2.1 h
23
87% lit
2.8 h
24
80% lit
3.3 h
25
72% lit
3.8 h
26
63% lit
4.1 h
27
53% lit
4.5 h
28
44% lit
4.8 h
29
34% lit
5.1 h
30
25% lit
5.4 h
31
16% 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 Mays

Casper needs Kp 8 for the average oval edge to sit overhead. 8 of the 930 May days from 1996 to 2025 (1%) 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 10%. Casper sits at 50.3 degrees geomagnetic. The lowest NOAA storm level whose typical viewing latitude reaches it is G3 (Kp = 7). By SWPC's rule the average oval edge is overhead only at Kp 8.

May across United States

No month-page town in United States has more civil night on May 15 than Casper; the national median is 7.6 hours. Coming from April (9.5 hours at Casper), May loses darkness, and June brings shorter nights (7.4 hours on the 15th).

Civil night on May 15 and May cloud, month-page towns in United States
Town	Civil night	Cloud
Casper	8.1 h	62%
Buffalo	8.1 h	65%
Portland, Maine	8.0 h	66%
Minneapolis	7.9 h	63%
Duluth	7.6 h	65%
Fargo	7.6 h	61%
Seattle	7.5 h	70%
Juneau	5.1 h	74%
Anchorage	3.8 h	79%
Eagle River	3.7 h	79%
Fairbanks	0.0 h	70%

Darkness and moon, every night

Casper, May 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
Sat May 1	8 h 44 min	6 h 3 min	7 h 14 min	4 h	19%
Sun May 2	8 h 41 min	5 h 59 min	7 h 33 min	4 h	12%
Mon May 3	8 h 39 min	5 h 55 min	7 h 54 min	4 h	6%
Tue May 4	8 h 36 min	5 h 51 min	8 h 19 min	4 h	2%
Wed May 5	8 h 33 min	5 h 48 min	8 h 33 min	4 h	0%
Thu May 6	8 h 31 min	5 h 44 min	8 h 11 min	4 h	1%
Fri May 7	8 h 28 min	5 h 40 min	6 h 55 min	3 h 39 min	4%
Sat May 8	8 h 26 min	5 h 36 min	5 h 46 min	2 h 32 min	10%
Sun May 9	8 h 23 min	5 h 33 min	4 h 49 min	1 h 36 min	19%
Mon May 10	8 h 21 min	5 h 29 min	4 h 3 min	51 min	28%
Tue May 11	8 h 18 min	5 h 25 min	3 h 27 min	16 min	39%
Wed May 12	8 h 16 min	5 h 22 min	2 h 57 min	0 min	51%
Thu May 13	8 h 13 min	5 h 18 min	2 h 31 min	0 min	62%
Fri May 14	8 h 11 min	5 h 15 min	2 h 8 min	0 min	72%
Sat May 15	8 h 9 min	5 h 11 min	1 h 45 min	0 min	81%
Sun May 16	8 h 6 min	5 h 8 min	1 h 21 min	0 min	89%
Mon May 17	8 h 4 min	5 h 4 min	55 min	0 min	95%
Tue May 18	8 h 2 min	5 h 1 min	24 min	0 min	98%
Wed May 19	8 h	4 h 57 min	0 min	0 min	100%
Thu May 20	7 h 57 min	4 h 54 min	20 min	0 min	99%
Fri May 21	7 h 55 min	4 h 51 min	1 h 18 min	22 min	97%
Sat May 22	7 h 53 min	4 h 47 min	2 h 7 min	1 h 12 min	92%
Sun May 23	7 h 51 min	4 h 44 min	2 h 46 min	1 h 53 min	87%
Mon May 24	7 h 49 min	4 h 41 min	3 h 19 min	2 h 26 min	80%
Tue May 25	7 h 48 min	4 h 38 min	3 h 45 min	2 h 53 min	72%
Wed May 26	7 h 46 min	4 h 35 min	4 h 7 min	3 h 17 min	63%
Thu May 27	7 h 44 min	4 h 32 min	4 h 27 min	3 h 37 min	53%
Fri May 28	7 h 42 min	4 h 29 min	4 h 46 min	3 h 57 min	44%
Sat May 29	7 h 41 min	4 h 26 min	5 h 4 min	4 h	34%
Sun May 30	7 h 39 min	4 h 24 min	5 h 24 min	4 h	25%
Mon May 31	7 h 38 min	4 h 21 min	5 h 47 min	4 h	16%

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

Questions

Can you see the northern lights in Casper in May?: On dark, clear nights with enough activity. 31 of 31 nights at Casper have civil darkness, and 1% of past May days reached Kp 8.
How dark is Casper in May?: Casper averages 8.1 hours of civil night a night in May 2027, from 8 h 44 min on the 1st to 7 h 38 min on the last night.
How cloudy is Casper in May?: NASA POWER's 2001 to 2020 climatology gives Casper's 1 degree cell 62% mean cloud in May, against 56% for the whole year. It is an all-hours average, not a forecast.
What is the best night in May 2027 for aurora in Casper?: By darkness and moon alone, May 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Casper. Activity on that date will only be known hours ahead.
Is May or June better in Casper?: By civil night times the clear share, May scores 3.1 hours at Casper and June 4.1. June 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.