a continuous count of days beginning with January 1, 4713 BC (-4712 CE), which is start of what is called the Julian period. The French scholar Joseph Justus Scaliger (1540-1609) introduced the Julian period in 1582 (the same year the Gregorian calendar was proclaimed), defining it to be 7980 years, the product of the 28-year cycle of the Julian calendar (after which the days of the week recur on the same dates), the 19-year Metonic cycle (after which the phases of the Moon recur on the same dates), and the 15-year indiction cycle (a unit of civil time in ancient Rome). It happens that 4713 BC is the last year in which all three cycles started simultaneously. In 1849 the British astronomer John Herschel introduced the Julian day as a means of providing an exact date for astronomical events independent of all calendars. The Julian day begins at noon Universal Time, and exact times of observations are expressed using decimal fractions of the Julian day. The first moment of the year 2004 CE, Universal Time, was JD 2 453 005.5. See also modified Julian day.

The day beginning at noon, Greenwich time, and ending at the next Greenwich noon. Set up in that way so that in Europe, where the idea originated, the Julian Day Number does not change during the night.

a time period used in astronomical circles, defined as the number of days since 1 January, 4713 BCE ( Before Common Era), with the first day defined as Julian day zero. The Julian day begins at noon UTC. Some scientists use the term julian day to mean the numerical day of the current year, where January 1 is defined as day 001.

The number of days, and fraction of a day, measured from noon on 1 January of the year 4713 B.C.

A Julian Day (also known as a Julian day Nukmber - JDN) is an integer number counting the days since Monday, January 1, 4713 BC in the Proleptic Julian Calendar (that is extending the Julian Calendar to dates before is offical use in 45 BC). This should not be confused with the "Julian calendar or the "Julian Date." the Julian Day was proposed by Joseph Scaliger in 1583, during the Gregorian calendar reform. The "Julian" in "Julian day" refers to Scaliger's father, Julius Scaliger.

The number of days (and fractions thereof) that have elapsed since noon on January 1, 4713 BC (Greenwich Mean Time). It is used to simplify the calculation of the time interval between two events. For example, 9:00 P.M. P.S.T. on January 1, 2000, was Julian day 2,451,545.71.

Astronomers simplify their timekeeping by merely counting the days, and not months and years. Each date has a Julian Day number (JD), beginning at noon, which is the number of elapsed days since January 1st, 4713 B.C. For instance, January 1st, 1993, was JD 2448989; January 2nd, 1993, was JD 2448990; and January 1st, 2000, was JD 2451545. [More Info

Calendar date based on a 365-day year, usually in the form ccyyddd; for example, 1996056 is February 25, 1996.

A unit of time within the Julian Dating System where the number of ephemeris days that have elapsed since 12h ephemeris time on January 1, 4713 B.C. JD for 1970 January 1 is 2440588.

The Julian Day is the number of days since the year -4712. The Julian Day begins at 12:00 Noon Greenwich mean time.

The number of each day, as reckoned consecutively since the beginning of the present Julian period on January 1, 4713 B.C. The Julian day is used primarily by astronomers to avoid confusion due to the use of different calendars at different times and places. The Julian day begins at noon, 12 hours later than the corresponding civil day. The day beginning at noon January 1, 1965, is Julian day 2,438,395.

The Julian day or Julian day number (JDN) is the (integer) number of days that have elapsed since the initial epoch at noon Universal Time (UT) Monday, January 1, 4713 BC in the proleptic Julian calendar This equals November 24, 4714 BC in the proleptic Gregorian calendar.. That noon-to-noon day is counted as Julian day zero. Thus the multiples of 7 are Mondays.