Can you see the northern lights in Joliet in August?

On dark, clear nights with enough activity. 31 of 31 nights at Joliet have civil darkness, and 0% of past August days reached Kp 8.

How dark is Joliet in August?

Joliet averages 9.1 hours of civil night a night in August 2027, from 8 h 30 min on the 1st to 9 h 49 min on the last night.

How cloudy is Joliet in August?

NASA POWER's 2001 to 2020 climatology gives Joliet's 1 degree cell 47% mean cloud in August, against 59% for the whole year. It is an all-hours average, not a forecast.

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

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

Is August or September better in Joliet?

By civil night times the clear share, August scores 4.8 hours at Joliet and September 5.9. September comes out ahead.

Joliet · August 2027

Northern lights in Joliet in August 2027

Answer

August gives Joliet 9.1 hours of civil night on the 15th, the 9th darkest of its 12 months, under 47% mean cloud. 0% of August days since 1996 reached Kp 8, enough for the oval edge to reach Joliet.

9.1 h

civil night, average night

SunCalc for 41.53, -88.08; NASA POWER; GFZ Kp

August against the rest of the year

4.3

4.1

4.0

3.7

3.2

3.4

4.1

4.8

5.9

5.1

5.0

4.1

August cloud at Joliet averages 47% in NASA POWER's 2001 to 2020 record, 12 points clearer than its yearly mean. September is Joliet's clearest month at 44%. By civil night times clear sky, August scores 4.8 hours at Joliet, 4th of 12. Minneapolis, 569 km away, averages 49%, cloudier by 2 points.

Civil night at Joliet starts August at 8 h 30 min and reaches 9 h 49 min by August 31 as the nights lengthen by 1.3 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 6.6 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 America/Chicago dates. Joliet gets 142 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 1 (4 h), Aug 2 (4 h), Aug 3 (4 h).

1
0% lit
8.5 h
2
1% lit
8.5 h
New
3
5% lit
8.4 h
4
11% lit
8.0 h
5
20% lit
7.6 h
6
29% lit
7.2 h
7
40% lit
6.8 h
8
50% lit
6.3 h
9
60% lit
5.7 h
10
70% lit
5.0 h
11
78% lit
4.2 h
12
86% lit
3.3 h
13
92% lit
2.3 h
14
96% lit
1.3 h
15
99% lit
0.2 h
16
100% lit
0.0 h
17
99% lit
0.0 h
Full
18
97% lit
0.0 h
19
92% lit
0.3 h
20
86% lit
0.7 h
21
79% lit
1.1 h
22
70% lit
1.6 h
23
60% lit
2.1 h
24
49% lit
2.8 h
25
38% lit
3.7 h
26
27% lit
4.8 h
27
17% lit
6.1 h
28
9% lit
7.4 h
29
3% lit
8.8 h
30
0% lit
9.8 h
31
0% lit
9.8 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

Joliet needs Kp 8 for the average oval edge to sit overhead. 3 of the 930 August days from 1996 to 2025 (0%) reached it in the GFZ Potsdam record, 7th of 12 months; storm days with Kp 5 or more made up 11%. Joliet sits at 50.4 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.

August across United States

No month-page town in United States has more civil night on August 15 than Joliet; the national median is 8.6 hours. Coming from July (7.9 hours at Joliet), August adds darkness, and the nights keep growing into September (10.5 hours on the 15th).

Civil night on August 15 and August cloud, month-page towns in United States
Town	Civil night	Cloud
Joliet	9.1 h	47%
Buffalo	9.0 h	56%
Portland, Maine	8.9 h	52%
Minneapolis	8.8 h	49%
Duluth	8.6 h	52%
Fargo	8.6 h	49%
Seattle	8.5 h	48%
Juneau	6.9 h	79%
Anchorage	6.3 h	79%
Eagle River	6.2 h	79%
Fairbanks	5.0 h	75%

Darkness and moon, every night

Joliet, 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	8 h 30 min	5 h 45 min	8 h 30 min	4 h	0%
Mon Aug 2	8 h 32 min	5 h 49 min	8 h 32 min	4 h	1%
Tue Aug 3	8 h 34 min	5 h 52 min	8 h 25 min	4 h	5%
Wed Aug 4	8 h 37 min	5 h 56 min	8 h	4 h	11%
Thu Aug 5	8 h 39 min	5 h 59 min	7 h 36 min	4 h	20%
Fri Aug 6	8 h 42 min	6 h 2 min	7 h 12 min	3 h 53 min	29%
Sat Aug 7	8 h 44 min	6 h 6 min	6 h 46 min	3 h 26 min	40%
Sun Aug 8	8 h 47 min	6 h 9 min	6 h 17 min	2 h 55 min	50%
Mon Aug 9	8 h 49 min	6 h 13 min	5 h 42 min	2 h 19 min	60%
Tue Aug 10	8 h 52 min	6 h 16 min	5 h	1 h 36 min	70%
Wed Aug 11	8 h 54 min	6 h 20 min	4 h 11 min	46 min	78%
Thu Aug 12	8 h 57 min	6 h 23 min	3 h 16 min	0 min	86%
Fri Aug 13	9 h	6 h 27 min	2 h 17 min	0 min	92%
Sat Aug 14	9 h 2 min	6 h 30 min	1 h 16 min	0 min	96%
Sun Aug 15	9 h 5 min	6 h 34 min	14 min	0 min	99%
Mon Aug 16	9 h 8 min	6 h 37 min	0 min	0 min	100%
Tue Aug 17	9 h 10 min	6 h 40 min	0 min	0 min	99%
Wed Aug 18	9 h 13 min	6 h 44 min	0 min	0 min	97%
Thu Aug 19	9 h 16 min	6 h 47 min	19 min	0 min	92%
Fri Aug 20	9 h 18 min	6 h 51 min	42 min	0 min	86%
Sat Aug 21	9 h 21 min	6 h 54 min	1 h 6 min	0 min	79%
Sun Aug 22	9 h 24 min	6 h 58 min	1 h 34 min	0 min	70%
Mon Aug 23	9 h 26 min	7 h 1 min	2 h 8 min	20 min	60%
Tue Aug 24	9 h 29 min	7 h 5 min	2 h 50 min	1 h 1 min	49%
Wed Aug 25	9 h 32 min	7 h 8 min	3 h 43 min	1 h 52 min	38%
Thu Aug 26	9 h 35 min	7 h 12 min	4 h 48 min	2 h 55 min	27%
Fri Aug 27	9 h 38 min	7 h 15 min	6 h 4 min	4 h	17%
Sat Aug 28	9 h 40 min	7 h 18 min	7 h 25 min	4 h	9%
Sun Aug 29	9 h 43 min	7 h 22 min	8 h 47 min	4 h	3%
Mon Aug 30	9 h 46 min	7 h 25 min	9 h 46 min	4 h	0%
Tue Aug 31	9 h 49 min	7 h 29 min	9 h 49 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 Joliet in August?: On dark, clear nights with enough activity. 31 of 31 nights at Joliet have civil darkness, and 0% of past August days reached Kp 8.
How dark is Joliet in August?: Joliet averages 9.1 hours of civil night a night in August 2027, from 8 h 30 min on the 1st to 9 h 49 min on the last night.
How cloudy is Joliet in August?: NASA POWER's 2001 to 2020 climatology gives Joliet's 1 degree cell 47% mean cloud in August, against 59% for the whole year. It is an all-hours average, not a forecast.
What is the best night in August 2027 for aurora in Joliet?: By darkness and moon alone, Aug 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Joliet. Activity on that date will only be known hours ahead.
Is August or September better in Joliet?: By civil night times the clear share, August scores 4.8 hours at Joliet and September 5.9. 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.