Without an astronomical or historical context, a "Julian date" given as "40" most likely means the fortieth day of a given Gregorian year, namely February 9.Other possible meanings of a "Julian date" of "40" include an astronomical Julian Day Number, or the year AD 40 in the Julian calendar, or a duration of 40 astronomical Julian years).Julian dates are expressed as a Julian day number with a decimal fraction added.It has been used by historians since its introduction in 1583 to convert between different calendars.
In contexts where a "Julian date" means simply an ordinal date, calendars of a Gregorian year with formatting for ordinal dates are often called "Julian calendars", but this could also mean that the calendars are of years in the Julian calendar system. For dates in the Julian calendar, see Julian calendar. For the comic book character Julian Gregory Day, see Calendar Man.For the artist and composer, see Julian Day (artist).Time intervals calculated from differences of Julian Dates specified in non-uniform time scales, such as Coordinated Universal Time (UTC), may need to be corrected for changes in time scales (e.g. Because the starting point or reference epoch is so long ago, numbers in the Julian day can be quite large and cumbersome.A more recent starting point is sometimes used, for instance by dropping the leading digits, in order to fit into limited computer memory with an adequate amount of precision.