Read the year
Know when to plant, without being told.
Everything for this step
- Field guide
- Navigation and the sky → 7 sections The sciences → 15 sections Seeds and the growing year → 5 sections Astronomy → 5 sections
- Builds
- None yet.
- Reference sheets
- None.
- Sciences it rests on
- Astronomy · Mathematics
- Track
- Crops and soil, level 2 of 7 · next: Open ground and hold fertility
Why this matters
Agriculture is a timing problem before it is a labour problem. Plant three weeks late and you halve the yield; plant before the last frost and you lose the lot. Every early agricultural society built an observatory of some kind, and they were not doing it for religion alone.
The shape of it
- Set a vertical post on level ground with a clear view of the horizon. Mark the tip of its noon shadow every few days for a year.
- The shortest noon shadow is midsummer; the longest is midwinter; the two days when the shadow tip crosses a straight east–west line are the equinoxes. You now have four fixed points in the year that never drift.
- Mark where the sun rises against the horizon at those four dates using cairns or notched posts. This turns your horizon into a permanent calendar readable by anyone, forever, with no instrument.
- Record the local events that actually matter, against that calendar: last spring frost, first autumn frost, first rain, ice-out, when specific trees bud and when specific birds arrive. Phenology — what the plants are doing — predicts planting date better than a fixed date does.
- Count days continuously in the log from an arbitrary day one. A continuous day count is more robust than a calendar of months and survives disagreement about what month it is.
- Teach the calendar to at least two people and cut it into something durable — see Writing.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Set a gnomon that will not move for a year
A vertical post on level ground with a clear view of the horizon, ideally to the east and west. Set it deep and firm — a post that shifts by a few degrees across the year destroys the record it exists to make.
Check it with a plumb line in two directions at right angles, and check it again each month. Clear the ground around its base and keep it clear: you will be marking shadow tips on it all year.
2 · Mark the noon shadow every few days for a full year
Local noon is the moment of the shortest shadow, not what any clock says. Watch the shadow shorten and lengthen, and mark the tip at its shortest with a peg or a scratched stone.
Do it every few days, and label each mark with its day number. The shortest noon shadow of the year is the June solstice; the longest is the December solstice (reversed in the southern hemisphere). The marks trace a line that is the year itself, written on the ground.
3 · Find the equinoxes from the shadow's path
On the two equinoxes, the shadow tip traces an almost perfectly straight east–west line across the day; on every other day it curves. The sun also rises due east and sets due west on those days.
That gives four fixed points in the year — two solstices and two equinoxes — from observation alone, with no instrument and no inherited calendar. Everything else is counting between them.
4 · Turn the horizon into a permanent calendar
From one fixed observing spot, mark where the sun rises against the horizon on each of the four dates — with cairns, notched posts, or by noting the hill or tree it clears.
The sunrise point walks north and south along the horizon through the year and stops and reverses at each solstice, moving very little for several days either side, so bracket the turn and take the middle.
Once built, this is readable by anyone, forever, with no instrument, no writing and no expert — which is the point. The observing spot must be marked as carefully as the horizon points; move it and the calendar is wrong.
5 · Keep one continuous day count
Count days from an arbitrary day one and never stop. A continuous count is more robust than months: it survives disagreement, illness, a hard winter and an argument about what month it is, and it makes every record comparable.
Cut it into something durable — a notched stick, a marked post, a written log — and have two people keep it independently, comparing weekly. A count kept in one head is lost the week that person is ill.
6 · Record what actually matters against the count
The calendar is only useful when local events are written against it. Record, every year, with the day number:
- Last spring frost and first autumn frost — the two dates that decide planting.
- Ice-out on the pond, first rain, first flood.
- Bud burst on named trees, first blossom, first bird arrivals.
- Sowing and harvest dates, and what the weather did to each.
After three years these are a working forecast. Soil temperature decides germination more than the date does — maize needs about 10 °C, beans and squash 15–16 °C, peas around 5 °C — so record soil readings against the day number too.
7 · Teach it to two people and cut it into something that lasts
A calendar held by one person is one illness away from a year of re-observation. Teach the whole method — the gnomon, the noon mark, the horizon points, the count — to at least two others, and have them demonstrate it rather than describe it.
Then make it durable: marks cut in stone or hardwood, not charcoal on a board. See writing and the durable record for what survives, and keep a copy of the horizon marks as a drawing in the record.