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
So actually **not** by measuring the sun. The Egyptians were the first to figure out that there were 365 days in a year. Before that calendars usually had 360 days because it more or less lined up with everything and the Babylonians used a base 60 number system that this fit well in. It’s also part of the reason we have 360 degrees in a circle. This was more based on observing the moon too. You’d have a new moon cycle roughly every 30 days, and 12 moon cycles would more or less line up with the sun being in sorta the same place and the seasons coming back around. Eventually this would fall out of sync since the moons cycle isn’t actually 30 days, and there’s not 360 days in a year. So sometimes they’d add an extra month here or there and it worked well enough.
But the Egyptians looked at the stars instead. They saw that the star Sirius appeared just above the horizon at dawn at the same time every 365 days. That lined up closely with the flooding of the Nile too, so it was significant beyond just being interesting. It gave them greater predictive power over important events. So they made a calendar with 12 lunar months, and then 5 extra days on top of that for 365 days total. They did know it came a day later every 4 years, but they just let that slide. The calendar fell behind a little bit every four years, but they could see by looking at Sirius when it had been a year and the Nile would flood again.
They put a lot of emphasis on observing the stars for largely religious reasons. So they could see pretty clearly when an important star appeared to rise in the same location. It’s more of a discrete event to them that they could see happened every 365 days than a measurement they had to try and get right with tools from 5000 years ago.
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