1. Historically, January began on Saturday because of julian calendar in ancient Rome. In julian calendar, a year is divided into 12 months, with January starting on Saturday and the last month (i.e. 12 months) ending on Sunday.

2. In reality: January starts from Saturday, and the rest time for the whole month is guaranteed. January begins on Monday, so many people will work for seven days after New Year's Day, which is not conducive to people's rest and health.