January 1 is far from the only New Year's Day. Many cultures have other New Years spread throughout the seasons:
In 2016, many of these holidays will appear on different dates than they did in 2015. In most cases, it’s because they are based on lunar calendars (like the Chinese, Jewish, and Islamic New Years are).
Our own American New Year is fixed to the Gregorian calendar, which Pope Gregory XIII established in 1582 to account for a discrepancy of 10 days that had accumulated since Julius Caesar had borrowed the Egyptians’ 12-months-and-365-days-plus-leap-years format. (Earth’s trip around the sun is — inconveniently — not quite 365.25 days long.)
Gregory XIII also moved the New Year from March 25 (the Feast of Annunciation) to January 1, where it still stands today.