I heard in the past, first from someone who'd studied permaculture, and then while listening to a recording of a Permaculture Design Course, that any given full moon will track the path of the sun in 6 months. So if you watch the full moon tonight, May 15th, you'll see what the sun will be doing around November 15th (which is the same as it'll be doing around January 26 on the mirror side of the winter solstice). I found this intriguing, and stashed the tip away, but haven't had reason to use it until now. Before committing myself to sleep deprivation tonight, I researched the veracity, and it does seem to check out.
I don't have a deep understanding of these big objects whirling in different patterns through space, but Jurgen Giesen explains it well: the moon and the sun are in almost the same plane with the earth (the moon might vary up to 5.5°?), and the full moon is opposite the sun in relation to the earth. So a full moon is about equivalent to the sun offset by 6 months.
I did some sanity checking (example sun info, example moon info) at timeanddate.com for Hilo, Hawai'i (year 2022), and the numbers are indeed the same within at most 4°:
| Date | Sun or Moon | Rise | Set | Peak altitude |
|---|---|---|---|---|
| Apr 15-16 | Full moon | 95°E | 262°W | 64°S |
| Oct 15 | Sun | 99°E | 261°W | 62°S |
| May 15-16 | Full moon | 111°ESE | 247°WSW | 54°S |
| Nov 15 | Sun | 109°ESE | 250°WSW | 52°S |
| Jun 13-14 | Full moon | 117°ENE | 242°WNW | 44°S |
| Dec 14 | Sun | 114°ENE | 246°WNW | 47°S |
| Dec 7-8 | Full moon | 63°ENE | 298°WNW | 84°N |
| Jun 7 | Sun | 65°ENE | 295°WNW | 87°N |
To see just the extremes of the sun's paths across your site, you only need to observe during the month of June or December. If you can watch the full moon close to a solstice, you'll see the other end of the sun's range that you're directly observing that month. For approximately monthly gradation, you only need about 3 months of observation starting or ending on a solstice, with two caveats:
- In temperate climates, the deciduous nature of many trees complicates predictions of what will actually get sun and shade.
- The moon's path varies a lot from one night to the next, so watching it even one day before or after it's full will be significantly less accurate. If the full moon falls on a cloudy night, you're out of luck.
Those caveats aside, these 2022 observations would let you envision a full year with approximately monthly gradation:
| Observe date | Sun or moon | Sun equivalent 1 | Sun equivalent 2 |
|---|---|---|---|
| Jun 13-14 | Full moon | Dec 13 | Dec 29 |
| Jun 21 | Sun | Jun 21 | Jun 21 |
| Jul 12-13 | Full moon | Jan 12 | Dec 1 |
| Jul 21 | Sun | May 21 | Jul 21 |
| Aug 11-12 | Full moon | Feb 11 | Nov 1 |
| Aug 21 | Sun | Apr 21 | Aug 21 |
| Sep 21 | Sun | Mar 21 | Sep 21 |
(Since the sun's path is identical on the equinoxes, March and September 21, there isn't much advantage in watching the full moon to predict the sun in those months.)
The same observation dates in chronological order of "equivalents" (observation dates entered on multiple lines since most cover two "equivalent" dates):
| Observe date | Sun or moon | Sun equivalent |
|---|---|---|
| Jul 12-13 | Full moon | Jan 12 |
| Aug 11-12 | Full moon | Feb 11 |
| Sep 21 | Sun | Mar 21 |
| Aug 21 | Sun | Apr 21 |
| Jul 21 | Sun | May 21 |
| Jun 21 | Sun | Jun 21 |
| Jul 21 | Sun | Jul 21 |
| Aug 21 | Sun | Aug 21 |
| Sep 21 | Sun | Sep 21 |
| Aug 11-12 | Full moon | Nov 1 |
| Jul 12-13 | Full moon | Dec 1 |
| Jun 13-14 | Full moon | Dec 13 |
| Jun 13-14 | Full moon | Dec 29 |
