For how many years have we known definitively what a year was? When was the first 'Happy new year!'? | AskHistorians Archive Observer

For how many years have we known definitively what a year was? When was the first 'Happy new year!'?

by SolarGoat

Searocksandtrees

hi! this may be worth x-posting to /r/AskAnthropology; meanwhile, you may be interested in this earlier post

Apparently, the world's 'oldest calendar' has been discovered. Can our experts on archaeology provide some context, more depth and an assessment of the findings?