Origin of calendar dating dating nebrasak
If you add the additional rule that years evenly divisible by 4000 are leap years, you obtain an average solar year of 365.24225 days per year which, compared to the actual mean year of 365.24219878, is equivalent to an error of one day over a period of about 19,500 years; this is comparable to errors due to tidal braking of the rotation of the Earth.
Astronomers, unlike historians, frequently need to do arithmetic with dates.
But the Julian day notation is so deeply embedded in astronomy that it is unlikely to be displaced at any time in the foreseeable future.
It is an ideal system for storing dates in computer programs, free of cultural bias and discontinuities at various dates, and can be readily transformed into other calendar systems, as the source code for this page illustrates.
Use Julian days and fractions (stored in 64 bit or longer floating point numbers) in your programs, and be ready for Y10K, Y100K, and Y1MM!
While any event in recorded human history can be written as a positive Julian day number, when working with contemporary events all those digits can be cumbersome.
In addition, there are constraints on which days of the week on which a year can begin and to shift otherwise required extra days to prior years to keep the length of the year within the prescribed bounds.
As a purely solar calendar, no attempt is made to synchronise the start of months to the phases of the Moon.
While one can't properly speak of “Gregorian dates” prior to the adoption of the calendar in 1582, the calendar can be extrapolated to prior dates.
The calendar thus accumulates one day of error with respect to the solar year every 128 years.
Being a purely solar calendar, no attempt is made to synchronise the start of months to the phases of the Moon.
As in the Julian calendar, days are considered to begin at midnight.