Status: beta
Julian Date Converter
Convert between Julian Date (JD), Modified (MJD), and Truncated (TJD) formats with split-part precision.
- timekeeping
- astronomy
- utilities
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Days since Jan 1, 4713 BC, Noon.
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JD - 2,400,000.5 (Starts at Midnight).
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JD - 2,440,000.5 (NIST standard).
Precision & Methodology
Standard floating-point Julian Dates suffer from precision issues when representing sub-millisecond time across thousands of years. This tool uses split-part arithmetic, keeping the integer (Day) and fractional (Time of Day) components separate during conversion to maintain maximum accuracy.
- JD: The fundamental astronomical epoch. Note that JD starts at 12:00:00 UTC.
- MJD: Widely used in geodesy and satellite tracking. Shifts JD to start at midnight.
- TJD: A truncated version used by NIST and NASA to save space while maintaining precision for modern eras.