Browse Definitions :
Definition

Julian date

Contributor(s): Preston A. Larimer and Ricardo Mediavilla

1) Not to be confused with the Julian calendar, a Julian date or day number is the number of elapsed days since the beginning of a cycle of 7,980 years invented by Joseph Scaliger in 1583. The purpose of the system is to make it easy to compute an integer (whole number) difference between one calendar date and another calendar date. The 7,980 year cycle was derived by combining several traditional time cycles (solar, lunar, and a particular Roman tax cycle) for which 7,980 was a common multiple. The starting point for the first Julian cycle began on January 1, 4713 B.C. (Gregorian calendar - expressed in the ISO date format as "-4713-01-01 G") and will end on January 22, 3268 (3268-01-22 G). The following day will begin the first day of the second Julian date period (or 7,980 year cycle).

A Julian date or day number for a certain time of day on January 9, 2001, looked like this:

2451919.3423000001348555  

meaning 2,451,919 elapsed days since the beginning of the Julian cycle. The ".3423000001348555" represented the time of day ("15:12:54 EST").

It is not certain whether the Julian date or day number system was named after Joseph Scaliger's father, Julius Caesar Scaliger, or after the Julian calendar. Julian day numbers are widely used in astronomy.

2) Commonly in computer programming, Julian date has been corrupted to mean the number of elapsed days since the beginning of a particular year. For example, in this usage, the Julian date for the calendar date of 1998-02-28 would be day 59.

This was last updated in September 2005

Continue Reading About Julian date

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

SearchCompliance

  • risk assessment

    Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

  • PCI DSS (Payment Card Industry Data Security Standard)

    The Payment Card Industry Data Security Standard (PCI DSS) is a widely accepted set of policies and procedures intended to ...

  • risk management

    Risk management is the process of identifying, assessing and controlling threats to an organization's capital and earnings.

SearchSecurity

  • tokenization

    Tokenization is the process of replacing sensitive data with unique identification symbols that retain all the essential ...

  • incident response

    Incident response is an organized approach to addressing and managing the aftermath of a security breach or cyberattack, also ...

  • Federal Information Security Management Act (FISMA)

    The Federal Information Security Management Act (FISMA) is United States legislation that defines a framework of guidelines and ...

SearchHealthIT

SearchDisasterRecovery

  • call tree

    A call tree is a layered hierarchical communication model that is used to notify specific individuals of an event and coordinate ...

  • Disaster Recovery as a Service (DRaaS)

    Disaster recovery as a service (DRaaS) is the replication and hosting of physical or virtual servers by a third party to provide ...

  • cloud disaster recovery (cloud DR)

    Cloud disaster recovery (cloud DR) is a combination of strategies and services intended to back up data, applications and other ...

SearchStorage

Close