Rata Die (from lat. - on the calculated day) - the number of days that have passed since the beginning of our era according to the Gregorian calendar extended into the past. Rata Die = 1 corresponds to January 1, 1 year of our era (01.01.0001).
Differences between Rata Die and Julian date
Rata Die (RD) is similar to Julian dates (JD) in the sense that the values are simple real numbers that increase by 1 every day. Systems differ fundamentally in that JD takes a certain value at a specific absolute time, while RD values can be different relative to the time zone . This makes RD more suitable for working with calendar dates. The reference points also differ: RD 1 - midnight (00:00) local time on January 1, 1 A.D. e. according to the proleptic Gregorian calendar, JD 0 is noon (12:00) universal time on January 1, 4713 BC. e. according to the proleptic Julian calendar . In the computer language REXX, the countdown starts at 0 at midnight (00:00) local time on January 1, 1 A.D. e. according to the proleptic Gregorian calendar.
Rata Die Forms
There are three different forms of RD. In this section, they are defined in terms of Julian dates.
The first form of RD is a continuously increasing fractional number that takes integers at midnight local time. This can be defined in terms of a Julian date as
- RD = JD - 1,721,424.5
In the second form, RD is an integer that represents the whole day, from midnight to midnight local time. This is the result of rounding the first form of RD towards negative infinity. This is the same as the relationship between Julian date and Julian day number (JDN). In this way:
- RD = floor (JD - 1,721,424.5),
where floor is the integer part .
In the third form, RD is an integer noon and cannot receive any other time of the day. It is defined as
- RD = JD - 1,721,425
where the RD value must be an integer, which limits the choice of JD. This RD form is used in the book to convert calendar dates between calendars that share days at different borders.
The book does not make a clear distinction between these three forms, it uses the abbreviation “RD” for all of them [1] .
The book does not say that RD is based on Greenwich Mean Time, but on page 10 it is argued that RD with a decimal fraction is called a moment, and the moment-from-jd function takes a floating-point number as an argument and returns an argument of minus 1721424.5; there is no way to take the timezone offset as an argument.
REXX
The DATE function of the computer language REXX can return the number of full days (that is, not including the current day), starting from the base date, January 1, 1 AD on the proleptic Gregorian calendar, if the option "Base" is specified. This function uses local, not Greenwich Mean Time. REXX does not use the name "Rata Die".
See also
- Lilian date
- Julian date
Notes
- ↑ Reingold, Edward. Calendrical Calculations / Edward Reingold, Nachum Dershowitz. - 3rd. - Cambridge University Press, 2008 .-- ISBN 0-521-70238-0 . (eng.)