In this short video, Anthony Murphy of Mythical Ireland demonstrates how a Neolithic astronomer, using the passage and chamber of Cairn T at Loughcrew, would have been able to see the effects of the fact that the year is 365.24 days long. Every year at equinox, the position of the sun changes slightly, and jumps back every fourth year.
This video accompanies a comprehensive article about how the 19-year Metonic Cycle of the moon would have been observable in the Neolithic. See the article (and other videos) here:
https://mythicalireland.com/blogs/ast...