Date Tab

Use the Date tab to select a function for converting between fractional and Julian dates, or extracting specific components from a fractional date. For additional details, see the Application Notes section below.

Date Tab options

Button	Syntax	Definition
Day and Month Options
Date Conversion
Fractional date (YYYY.yy)	date(year,month,day)	Converts (Year,Month,Day) to Fractional date.
Extract from Fractional Date
Year (YYYY)	date_year(fractional date)	Extracts Year from Fractional date.
Month (MM)	date_month(fractional date)	Extracts Month from Fractional date.
Day (DD)	date_day(fractional date)	Extracts Day from Fractional date.
Convert Date
Fractional date (YYYY.yy)	date_from_long(days)	Converts Julian date to Fractional date.
Julian date (DDDD)	date_to_long(fractional date)	Converts Fractional date to Julian date.
Day of year option
Day of Year Options
Date Conversion
Fractional date (YYYY.yy)	date_from_day_of_year(year,day_of_year)	Converts (Year, Day of the year) to Fractional date.
Extract from Fractional Date
Year (YYYY)	date_year(fractional date)	Extracts Year from Fractional date.
Day of the year (DY)	date_day_of_year(fractional date)	Extracts Day of Year from Fractional date.
Convert Date
Fractional date (YYYY.yy)	date_from_long(days)	Converts Julian date to Fractional date.
Julian date (DDDD)	date_to_long(fractional date)	Converts Fractional date to Julian date.

Application Notes

Fractional Date

The Fractional date (or fractional years) can be calculated from year, month, and day. Alternatively it can be converted from year and day-of-year.

A basic algorithm to calculate fractional years—accounting for leap years— using the current number of days and the total number of days in that year is:

Year + (days/total_days_in_year)

Julian Date

To convert a fractional date to a Julian date, use the date_to_long(fractional date) function.

Julian dates are primarily used for arithmetic date operations involving day-based calculations. The result can be converted back to a fractional date if needed.

Julian time begins at 12:00 noon on 1 January, 4713 BCE, marking the convergence of three calendrical systems: the Julian, Gregorian, and Roman Indiction calendars.

Epoch Days & Conversion

In modern computing, the most commonly used reference point is Epoch time, which begins at midnight on 01 January 1970.

To reconcile Epoch days with Julian time (starting from noon on 01/01/-4713), add 2440587.5 days in the conversion equation:

Julian_date = date_from_long(Epoch_days + 2440587.5);