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.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • internal audit (IA)

    An internal audit (IA) is an organizational initiative to monitor and analyze its own business operations in order to determine ...

  • pure risk (absolute risk)

    Pure risk, also called absolute risk, is a category of threat that is beyond human control and has only one possible outcome if ...

  • risk assessment

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

SearchSecurity

  • phishing

    Phishing is a form of fraud in which an attacker masquerades as a reputable entity or person in email or other communication ...

  • vulnerability disclosure

    Vulnerability disclosure is the practice of publishing information about a computer security problem, and a type of policy that ...

  • incident response

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

SearchHealthIT

SearchDisasterRecovery

  • business continuity and disaster recovery (BCDR)

    Business continuity and disaster recovery (BCDR) are closely related practices that describe an organization's preparation for ...

  • business continuity plan (BCP)

    A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

  • call tree

    A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

SearchStorage

  • flash memory

    Flash memory, also known as flash storage, is a type of nonvolatile memory that erases data in units called blocks.

  • NAND flash memory

    NAND flash memory is a type of nonvolatile storage technology that does not require power to retain data.

  • NOR flash memory

    NOR flash memory is one of two types of nonvolatile storage technologies.

SearchSolidStateStorage

  • hybrid hard disk drive (HDD)

    A hybrid hard disk drive is an electromechanical spinning hard disk that contains some amount of NAND Flash memory.

Close