Julian Date

What Does Julian Date Mean?

Julian date, also commonly called as Julian day, refers to the number of days passed since the beginning of a self-created cycle of 7980 years. This concept was introduced by Joseph Scaliger in 1538 and its importance is integral in number computation by determining the difference between two known dates. It is largely used in computers and astronomy.

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Techopedia Explains Julian Date

Julian date is often confused with the Julian calendar, which was introduced by Julius Caesar in 45 B.C. to bring about reform in the Roman Empire. Julian date is the difference (or modulus) of time in days lapsed since the start of the 7,980-year cycle. This 7,980 years is calculated with several traditional time cycles (solar, lunar and a Roman tax cycle) for which 7,980 was a common multiple. The current Julian cycle started on January 1, 4713 B.C. (Gregorian calendar) and will end on January 22, 3268 A.D.

Julian date is commonly used in computer science to calculate the difference between days, since all numbers in the system are consecutive integers.

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.