The Julian and Modified Julian Dates

Résumé du livre

For many astronomical and geodetic purposes it is important to know the time elapsed between the events under study. The calendar we use today, with its varying number of days in the month and complex rules governing leap years, is most inconvenient for this purpose, and so for much of the twentieth century astronomers have used the sequence of 'Julian day numbers' to denote the days (beginning with Greenwich mean noon) on which events occur. Instants within a given day are assigned a Julian Date (JD), which is the Julian day number plus the fraction of the day since the preceding noon, and the time elapsed between two events is simply the difference between their JDs.