Why do so many people ring in the new year on Jan. 1?

A 13,600-year-old mastodon skull is unearthed in an Iowa creek
16th-century compass unearthed in Poland may have belonged to Copernicus
Researchers say they've found the surprising source of a key piece of Stonehenge
The world's oldest solar calendar may have been unearthed in Turkey
Ancient pot of gold unearthed in Turkey hints at ‘gravest misfortune,’ researchers say

How can you make the most of leap day? NPR listeners have a few ideas
Why do we leap day? We remind you (so you can forget for another 4 years)