How did they know how many days were a year in the past?

Question

I know that the seasons were indicators but how did they know precisely to the day how much a year was.

Edit: Copying from a response I made:
“Thanks for the response!
But I still have a doubt cause most of the reponses are to measure it in certain way and wait until the sun goes back to its initial position, and I get how measuring its easy by doing it over a long period of time but the difference between 2 days seems kind of difficult to notice, like when the sun got back to its position and people were like “yeah it looks about the same as how it started” and then they observed the next day and it looked exactly the same, how did they decide a specific day.
I guess my question is more about how they achieved such precission rather than the method”

In: Earth Science

Answer 1

You track how long it takes the sun to return to the same position in the sky.
There are a bunch of ways to do this. Some examples include:
1 – the sundial approach: Stick a stick into the ground, each day when the sun gets as high as it gets for that day (i.e. noon) mark the location where the shadow of the stick ends. When the shadow is at its longest/shortest for the year you’ve reached a solstice. Record the amount of time between equivalent solstices and you’ve measured a year.
2 – the Manhattanhenge approach – Find a nice clear area. Put a stick in the ground. Wait until it’s sunset and put a 2nd stick in the ground so that when you stand at the 1st stick the sun is directly in line with the 2nd stick. Wait. Note the days when when the sunset is inline with the 2nd stick while you stand at the first stick you will know you’ve passed exactly one year. If there is one such point per set of seasons then the time between them is a year. if there are two such points per set of seasons then the time between every other point is a year.