A Julian date(JD) is the elapsed time in days and fractions of a day since January 1, 4713 BC Greenwich noon. The purpose of the Julian date is to make it easy for computing difference between one calendar date and another calendar date.
A Julian date for a certain time of day on May 28, 2012 looks like this:
Here, 2456075 is the number of days elapsed since the beginning of the Julian cycle(i.e. January 1, 4713 BC Greenwich noon) and “.74082” represents the time of the day.
Julian date is widely used in the fields of earth sciences, computer programming, astronomy, military and food industry.
In computer programming, the meaning of Julian date changes sometimes. Julian date is considered to be the number of elapsed days since the beginning of a particular year. For example, the Julian date in 3-digit format for the calendar date of 2012-02-15 would be 46 or 046.
Many applications store dates in 5-digit long Julian format, which consists of a 2 digit year and a 3 digit day-of-year number. For example, 28-May-2012 is stored as 12148 or 14812, since 28th May is the 148th day of the year and 12 represents last two digits of the year.