Are there really 13 calendar months? Does the new year really start in January?

Or do the orientation to 12 months and the beginning of the new year in January serve rather to keep us out of our natural rhythm?

Why is our September considered the ninth month when Sept stands for seven?

Okt stands for Eight.
Nov stands for Nine.
Dec stands for Ten.
...

Watch the video and feel for yourself.
@JFK_Q17