Common year starting on Tuesday
A common year starting on Tuesday is any non-leap year (i.e. a year with 365 days) that begins on Tuesday, 1 January, and ends on Tuesday, 31 December. Its dominical letter hence is F. The current year, 2019, is a common year starting on Tuesday in the Gregorian calendar. The last such year was 2013 and the next such year will be 2030, or, likewise, 2014 and 2025 in the obsolete Julian calendar, see below for more. Any common year that starts on Sunday, Monday or Tuesday has two Friday the 13ths. This common year contains two Friday the 13ths in September and December. Leap years starting on Monday share this characteristic. From July of the year that precedes this year until September in this type of year is the longest period (14 months) that occurs without a Friday the 13th. Leap years starting on Saturday share this characteristic, from August of the common year that precedes it to October in that type of year.
French Republican calendar
and:
These two specifications are incompatible, as leap years defined by the autumnal equinox in Paris do not recur on a regular four-year schedule. Thus, the years III, VII, and XI were observed as leap years, and the years XV and XX were also planned as such, even though they were five years apart.
A fixed arithmetic rule for determining leap years was proposed in the name of the Committee of Public Education by Gilbert Romme on 19 Floréal An III (8 May 1795). The proposed rule was to determine leap years by applying the rules of the Gregorian calendar to the years of the French Republic (years IV, VIII, XII, etc. were to be leap years) except that year 4000 (the last year of ten 400-year periods) should be a common year instead of a leap year. Shortly thereafter, he was sentenced to the guillotine, and his proposal was never adopted and the original astronomical rule continued, which excluded any other fixed arithmetic rule. The proposal was intended to avoid uncertain future leap years caused by the inaccurate astronomical knowledge of the 1790s (even today, this statement is still valid due to the uncertainty in ΔT). In particular, the committee noted that the autumnal equinox of year 144 was predicted to occur at 11:59:40 pm local apparent time in Paris, which was closer to midnight than its inherent 3 to 4 minute uncertainty.