In 2021, the best dates and times for observing the zodiacal light are listed in the calendar below. The sky must be very clear with little or no light pollution. The specific times listed are for Dodgeville, Wisconsin (42° 58′ N, 90° 08′ W).
Here’s a nicely-formatted printable PDF file of the zodiacal light calendar:
| January 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | |||||
| 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| 10 | 11 | 12 | 13 | 14 | 15 | 16 |
| 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| 24 | 25 | 26 | 27 | 28 | 29 | 30 Zodiacal Light 6:49 – 7:26 p.m. West |
| 31 Zodiacal Light 6:50 – 7:50 p.m. West |
| February 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 Zodiacal Light 6:51 – 7:51 p.m. West |
2 Zodiacal Light 6:52 – 7:52 p.m. West |
3 Zodiacal Light 6:53 – 7:53 p.m. West |
4 Zodiacal Light 6:54 – 7:54 p.m. West |
5 Zodiacal Light 6:56 – 7:56 p.m. West |
6 Zodiacal Light 6:57 – 7:57 p.m. West |
|
| 7 Zodiacal Light 6:58 – 7:58 p.m. West |
8 Zodiacal Light 6:59 – 7:59 p.m. West |
9 Zodiacal Light 7:00 – 8:00 p.m. West |
10 Zodiacal Light 7:02 – 8:02 p.m. West |
11 Zodiacal Light 7:03 – 8:03 p.m. West |
12 Zodiacal Light 7:04 – 8:04 p.m. West |
13 |
| 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 28 Zodiacal Light 7:23 – 7:36 p.m. West |
| March 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 Zodiacal Light 7:25 – 8:25 p.m. West |
2 Zodiacal Light 7:26 – 8:26 p.m. West |
3 Zodiacal Light 7:27 – 8:27 p.m. West |
4 Zodiacal Light 7:28 – 8:28 p.m. West |
5 Zodiacal Light 7:29 – 8:29 p.m. West |
6 Zodiacal Light 7:31 – 8:31 p.m. West |
|
| 7 Zodiacal Light 7:32 – 8:32 p.m. West |
8 Zodiacal Light 7:33 – 8:33 p.m. West |
9 Zodiacal Light 7:34 – 8:34 p.m. West |
10 Zodiacal Light 7:36 – 8:36 p.m. West |
11 Zodiacal Light 7:37 – 8:37 p.m. West |
12 Zodiacal Light 7:38 – 8:38 p.m. West |
13 Zodiacal Light 7:40 – 8:40 p.m. West |
| 14 Zodiacal Light 8:41 – 9:41 p.m. West |
15 | 16 | 17 | 18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 28 | 29 | 30 Zodiacal Light 9:03 – 10:03 p.m. West |
31 Zodiacal Light 9:04 – 10:04 p.m. West |
| April 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 Zodiacal Light 9:05 – 10:05 p.m. West |
2 Zodiacal Light 9:07 – 10:07 p.m. West |
3 Zodiacal Light 9:08 – 10:08 p.m. West |
||||
| 4 Zodiacal Light 9:10 – 10:10 p.m. West |
5 Zodiacal Light 9:11 – 10:11 p.m. West |
6 Zodiacal Light 9:13 – 10:13 p.m. West |
7 Zodiacal Light 9:14 – 10:14 p.m. West |
8 Zodiacal Light 9:16 – 10:16 p.m. West |
9 Zodiacal Light 9:17 – 10:17 p.m. West |
10 Zodiacal Light 9:19 – 10:19 p.m. West |
| 11 Zodiacal Light 9:20 – 10:20 p.m. West |
12 Zodiacal Light 9:22 – 10:22 p.m. West |
13 Zodiacal Light 9:24 – 10:24 p.m. West |
14 | 15 | 16 | 17 |
| 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| 25 | 26 | 27 | 28 | 29 | 30 |
| May 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | ||||||
| 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 23 | 24 | 25 | 26 | 27 | 28 | 29 |
| 30 | 31 |
| June 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | ||
| 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| 13 | 14 | 15 | 16 | 17 | 18 | 19 |
| 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| 27 | 28 | 29 | 30 |
| July 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | ||||
| 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 |
| 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| 25 | 26 | 27 | 28 | 29 | 30 | 31 |
| August 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| 15 | 16 | 17 | 18 | 19 | 20 | 21 |
| 22 | 23 | 24 | 25 | 26 | 27 | 28 |
| 29 | 30 | 31 |
| September 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |||
| 5 | 6 Zodiacal Light 3:52 – 4:52 a.m. East |
7 Zodiacal Light 3:53 – 4:53 a.m. East |
8 Zodiacal Light 3:54 – 4:54 a.m. East |
9 Zodiacal Light 3:56 – 4:56 a.m. East |
10 Zodiacal Light 3:57 – 4:57 a.m. East |
11 Zodiacal Light 3:58 – 4:58 a.m. East |
| 12 Zodiacal Light 4:00 – 5:00 a.m. East |
13 Zodiacal Light 4:01 – 5:01 a.m. East |
14 Zodiacal Light 4:02 – 5:02 a.m. East |
15 Zodiacal Light 4:04 – 5:04 a.m. East |
16 Zodiacal Light 4:05 – 5:05 a.m. East |
17 Zodiacal Light 4:06 – 5:06 a.m. East |
18 Zodiacal Light 4:08 – 5:08 a.m. East |
| 19 Zodiacal Light 4:59 – 5:09 a.m. East |
20 | 21 | 22 | 23 | 24 | 25 |
| 26 | 27 | 28 | 29 | 30 |
| October 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | |||||
| 3 | 4 | 5 Zodiacal Light 4:28 – 5:28 a.m. East |
6 Zodiacal Light 4:30 – 5:30 a.m. East |
7 Zodiacal Light 4:31 – 5:31 a.m. East |
8 Zodiacal Light 4:32 – 5:32 a.m. East |
9 Zodiacal Light 4:33 – 5:33 a.m. East |
| 10 Zodiacal Light 4:34 – 5:34 a.m. East |
11 Zodiacal Light 4:35 – 5:35 a.m. East |
12 Zodiacal Light 4:37 – 5:37 a.m. East |
13 Zodiacal Light 4:38 – 5:38 a.m. East |
14 Zodiacal Light 4:39 – 5:39 a.m. East |
15 Zodiacal Light 4:40 – 5:40 a.m. East |
16 Zodiacal Light 4:41 – 5:41 a.m. East |
| 17 Zodiacal Light 4:42 – 5:42 a.m. East |
18 Zodiacal Light 5:03 – 5:43 a.m. East |
19 | 20 | 21 | 22 | 23 |
| 24 | 25 | 26 | 27 | 28 | 29 | 30 |
| 31 |
| November 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 Zodiacal Light 5:03 – 6:03 a.m. East |
5 Zodiacal Light 5:04 – 6:04 a.m. East |
6 Zodiacal Light 5:05 – 6:05 a.m. East |
|
| 7 Zodiacal Light 4:06 – 5:06 a.m. East |
8 Zodiacal Light 4:07 – 5:07 a.m. East |
9 Zodiacal Light 4:08 – 5:08 a.m. East |
10 Zodiacal Light 4:09 – 5:09 a.m. East |
11 Zodiacal Light 4:10 – 5:10 a.m. East |
12 Zodiacal Light 4:12 – 5:12 a.m. East |
13 Zodiacal Light 4:13 – 5:13 a.m. East |
| 14 Zodiacal Light 4:14 – 5:14 a.m. East |
15 Zodiacal Light 4:15 – 5:15 a.m. East |
16 Zodiacal Light 4:16 – 5:16 a.m. East |
17 Zodiacal Light 5:06 – 5:17 a.m. East |
18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 28 | 29 | 30 |
| December 2021 |
| SUN | MON | TUE | WED | THU | FRI | SAT |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |||
| 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| 26 | 27 | 28 | 29 | 30 | 31 |
The best nights to observe the zodiacal light at mid-northern latitudes occur when the ecliptic plane intersects the horizon at an angle of 60° or steeper. The dates above were chosen on that basis, with the Sun at least 18° below the horizon and the Moon below the horizon being used to calculate the times. An interval of time of one hour either before morning twilight or after evening twilight was chosen arbitrarily because it is the “best one hour” for observing the zodiacal light. The zodiacal light cone will be brightest and will reach highest above the horizon when the Sun is 18° below the horizon (astronomical twilight), but no less.
If you are interested in calculating the angle the ecliptic makes with your horizon for any date and time, you can use the following formula:
where I is the angle between the ecliptic and the horizon, ε is the obliquity of the ecliptic, φ is the latitude of the observer, and θ is the local sidereal time (the right ascension of objects on the observer's meridian at the time of observation).
Here’s a SAS program I wrote to do these calculations:
References
Meeus, J. Astronomical Algorithms. 2nd ed., Willmann-Bell, 1998, p. 99.