Definitions of Julian dates

The term “Julian date” historically has been used by business users to denote the year and sequential day of the year.

For astronomers, “Julian date” is the number of days since noon GMT on Jan 1, 4713 BCE. This date was chosen because it is before recorded history.

Since 1988, ISO 8601 defines current Julian date usage as astronomers use it. This usage is becoming more common than the business use of Julian date – now called “Ordinal date”.

SAS functions, informats and formats

• DATEJUL Function
• JULDATE Function
• JULDATE7 Function
• JULIANw. Informat
• JULDAYw. Format
• JULIANw. Format

The items above all refer to what is now called “Ordinal date”. There are no current plans to change the names or functionality of these items.

SAS Date Values

A SAS date is a value that represents the number of days between January 1, 1960, and a specified date. SAS can perform calculations on dates ranging from A.D. 1582 to A.D. 19,900. Dates before January 1, 1960, are negative numbers; dates after are positive numbers.

• SAS date values account for all leap year days, including the leap year day in the year 2000.
• SAS date values can reliably tell you what day of the week a particular day fell on as far back as September 1752, the most recent time when the calendar was adjusted by dropping several days. SAS day-of-the-week and length-of-time calculations are accurate in the future to A.D. 19,900.

Conversion between SAS date values and Julian Date values

When the date falls in the range that can be represented as a valid SAS date, convert to Julian date by adding 2436934.5 to the SAS date value. The .5 compensates for the difference between the beginning of the day for a SAS date value (midnight) and beginning of a Julian Day (noon). If the date cannot be represented as a SAS date, you must derive your own formula.

Operating System and Release Information

data _NULL_;
sas_date = '31jan2010'd;                 /* SAS Date input to formula */
julian_date = ceil(sum(sas_date,2436934.5));/* formula for Julian Day */

/* print results in SAS log */
put sas_date= date9.  ' Ordinal date-formatted: ' 
    sas_date julian7. ' ' julian_date= ;
run;

sas_date=31JAN2010  Ordinal date-formatted: 2010031 julian_date=2455228