Calendars and time
Julian Century
Direct answer
Julian Century: A Julian Century is an exact interval of 36,525 days, equal to 100 Julian years of 365.25 days each.
A Julian Century is exactly 36,525 days in astronomical formulas.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Reduced Julian Date, Julian Epoch, Calendar, Julian Date
A Julian Century is exactly 36,525 days in astronomical formulas.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Julian Century
Astronomical standards adopted fixed Julian years and centuries to simplify polynomial expressions over long intervals.
Why Julian Century matters
Julian Century gives precession, nutation, and ephemeris formulas a fixed unit independent of variable civil-century lengths.
How to read Julian Century
Julian Century applies when a formula defines time T from an epoch such as J2000.0.
Julian Century in practice: an example
A formula may set T equal to the number of Julian days since J2000.0 divided by 36,525.
Where readings of Julian Century go wrong
A common error is to replace a Julian Century with the calendar interval between arbitrary century-number years.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory Circular 179: The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models - Technical reference for TAI, TT, TCG, TCB, TDB, UT1, sidereal time, epochs, and Earth rotation.
- U.S. Naval Observatory: Julian Date Converter - Official explanation of Julian dates and conversion between calendar dates and continuous day counts.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Use the formula defined century
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More in Calendars & Timekeeping
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- Synodic Month
- Week Number
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- Earth Rotation Angle
- Greenwich Sidereal Time
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Common questions
What is a Julian Century?
A Julian Century is an exact interval of 36,525 days, equal to 100 Julian years of 365.25 days each.
What do people get wrong about a Julian Century?
A common error is to replace a Julian Century with the calendar interval between arbitrary century-number years.
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