Seeing into the future: full moon as sun proxy

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