From Wikipedia,
“It is believed that Julius Caesar first proposed the idea of having January 1 as the first day of the year way back in 46 BC. This is because the month of January has been named after the Roman God Janus. Janus is personified as a two-faced person, one face facing the front and [...]

I hope it will be happy, but is it New Year at all? Why do we celebrate it on 1st January? I had to find out more than I already knew, which wasn’t much. 
Basically, the length of a year according to the Julian Calendar was too long, and after thirteen centuries of use, the actual vernal [...]