January ('Janvarus' in Latin) is named in the honour of Roman God Yanus. It is the first month in the Gregorian calendar, which was adopted in 1582.
By the order of the Russian tsar Peter I, the Gregorian calendar was replaced by the Julian calendar in Russia. According to that order Jan. 1 - the date of Jesus's birth - was declared the beginning of the year and the 18th century started from January 1, 1701.
The calendar was officially adopted in the former Soviet Union by the decree of V.I. Lenin in 1918. Thus, if the New Year started on Jan. 13 till that period, now the difference is removed and Jan.1 is determined as New Year. Jan. 1 is day off.
The same calendar is still applied in the Republic of Azerbaijan even after it gained its independence and Jan. 1 is marked as day off.