[bsimpson]

It's wild to think about how different things were in pre-modern times.

There are no computers, sensors, watches, or spaceships. There are also no TV-style distractions, and a lot more people are growing food. When would you notice that the longest day of the year is a few days away from what the books say it's supposed to be?

For that matter, the printing press was only a century old. How well-known was it that particular days are meant to be the longest or shortest of the year?

[turtletontine]

In an agrarian economy people are definitely much MORE attuned to the cycles of the seasons. If your town always starts planting crop X two weeks before the solstice, and the harvest festival is the week after the equinox, you’re going to keep track of these things.

[quuxplusone]

Yeah, but I took the parent comment as a non-rhetorical question. Say you were one of these "MORE attuned" people of the past: how long [literally] do you think it would take you to notice that the calendar was drifting? Like, if the calendar says the equinox should be on Monday, but in fact it's actually technically more like Tuesday, would you notice? What if it was technically on Wednesday?

If the rate of drift was like 5 days per year, then sure, people'd probably notice in a year or two — three tops, right? But how fast would the drift be? It's a question about how much people can detect small changes in daylight and how big the change actually is.

I also observe that we put up with tons of drift in our months: the new moon is hardly ever on the first of the month! And that's really easy to detect (within a day or two). So maybe people would notice a drift relative to the seasonal cycle and just not mind, the way we don't mind a drift relative to the lunar cycle.

[phainopepla2]

I think that when OP said "When would you notice" they meant you the reader in contemporary times, to draw attention to the high level of attunement you're referring to

[bombcar]

If I recall correctly - it was surprisingly well known (in fact it was a common way to make fun of "lettered" people because they'd claim dates that were obviously silly; everyone knew when the solstice was).

Some of the earliest things we have a sun-based calendar trackers, which need not be more complicated than a stick and a rock (meaning millions more have not survived).