Time in General
Several different time scales are in use, which are more or less adapted to a specific use. These are
- Gregorian Calendar
- This is is calendar which we use in everyday applications, with dates given as day, month, year (counted since some conventional day of birth of Jesus Christ), hours, minutes and seconds. The gregorian calendar was made the official calendar of christendom on 15. October 1582 by decree of Pope Gregory XIII (see Wikipedia). It replaced the older Julian Calendar. Some confusion about dates in the 16th century arises from the fact that defferent countries implementes the gregorian calendar at different times. in the calendar module, the 15. Oct. 1582 is hard-wired as the change date. The rules for leap years in the greogiran calendar are implemented in the MKLEAPYEAR routine.
- Day of Year (DOY, Julian Day)
- To have a more continuous time scale within a single year, the Day of Year counting (sometimes called Julian Day, causing confusion with the Julian Date) was introduced. the 1st Janury is day 1 on DOY counting and the 31st of December is DOY 365 or DOY 366, depending on the year being a leap year or a regular year. Transformation between y/m/d and DOY counting is done using routines
MKYDOY2YMDHMS
and MKDAYNO.
- Julian Date
- The Julian Date is a continuous counting of days since 01.01.-4712, 12:00. Days in JD begin at 12:00, not at 00:00, because the astronomers that invented this scale didn't want the date to change during their nightly observation time. JDs can have fractional parts. Transformation between y/m/d and JD is done using routines
MKJD
and MKJD2YMD.
- Seconds since a reference time
- in LOCSMITH, time is measured in seconds (instead of days) since a reference time which is defined as a global constant and delivered by the
MKLSCONSTANTS
routine.
Call mklsconstants('ReferenceDay') to get this reference time.
eof.