Convert gregorian year to stellar year

Common time conversion mistakes

• A year is not exactly 52 weeks: 365 days is 52 weeks plus one day, and a leap year 52 weeks plus two. That extra day is why the same date shifts one weekday each year. When spreading a yearly amount per week, use 52.18 weeks per year.
• There are several year definitions: the Julian year is exactly 365.25 days, the Gregorian calendar year 365.2425, and the tropical year about 365.2422 days. For everyday use the differences are negligible, but they matter in astronomy, the light-year, for instance, is defined using the Julian year.