Dictionary term
Modified Julian Date
Direct answer
Modified Julian Date: Modified Julian Date, or MJD, equals Julian Date minus 2,400,000.5, placing its day boundary at midnight rather than noon.
MJD is a shortened midnight-based form of Julian Date.
MJD is a shortened midnight-based form of Julian Date.
A cycle or timeline schematic for comparing the named timekeeping concept.Quick reference
- Use when
- Use Modified Julian Date in astronomy and geodesy while always naming the associated time scale, such as UTC, TT, or TDB.
- Do not use it for
- Do not drop the 0.5 in the conversion or omit the time scale at high precision.
- Reference category
- Calendars & Timekeeping
- Related terms
- Unix Time, Reduced Julian Date, Calendar, Julian Date
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The story behind Modified Julian Date
MJD was introduced in the nineteenth century and has an epoch at 1858 November 17 00:00.
Modified Julian Date in spiritual tradition
Spiritually, MJD shows how changing a reference origin can make data easier to handle without changing the instant itself.
Modified Julian Date: fact and faith, kept distinct
This is a factual calendar, astronomy, Earth-science, cultural-history, or observational reference. It can support wonder and practical planning without becoming a claim of fate, spiritual causation, or private revelation.
Modified Julian Date in numerology
Modified Julian Date is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Modified Julian Date matters
It reduces large day numbers and aligns integer changes with civil midnight for many scientific datasets.
Where interpretation stops
Modified Julian Date is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
Sources and editorial method
Research references used for this entry include:
- NASA Goddard: Modified Julian Dates - NASA explanation of JD and MJD conventions and their reference epochs.
- 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
- Also appears in
- Calendars & Timekeeping
- Aliases
- None listed
- Last updated
- 2026-07-16
Convert JD and MJD correctly
Modified Julian Date in a book is one thing; Modified Julian Date in your own birth chart is your life. The Oracle casts your real chart and tells you what it means for your love, your work, and your year ahead, in conversation, free.
Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Sidereal Day
- Tropical Month
- Anomalistic Month
- Dominical Letter
- Equation of Time
- Intercalary Day
- Leap Second
Common questions
What is Modified Julian Date?
Modified Julian Date, or MJD, equals Julian Date minus 2,400,000.5, placing its day boundary at midnight rather than noon.
How is Modified Julian Date used in an almanac?
Use Modified Julian Date in astronomy and geodesy while always naming the associated time scale, such as UTC, TT, or TDB.
What should I avoid when interpreting Modified Julian Date?
Do not drop the 0.5 in the conversion or omit the time scale at high precision.
