Astronomical Julian Day & MJD Converter
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Convert calendar Gregorian dates into astronomical Julian Day Number (JDN) and Modified Julian Day (MJD).
Julian Date (JD)
2460321.5
Modified Julian Date (MJD)
60321.0
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Direct In-Browser Handoff
Unix Epoch & Timestamp Conversion Suite
Chain this tool with complementary private browser utilities for a complete zero-server workflow:
Helpful Examples
Convert Current Date
Calculate current Julian Day Number
TodayHow to Use the Astronomical Julian Day & MJD Converter
Compute continuous day counts used in astronomy and satellite orbit tracking. Converts calendar dates and UTC times into Julian Date (JD), Julian Day Number (JDN), and Modified Julian Date ($MJD = JD - 2400000.5$).
Privacy & Data Processing Notice
No user data leaves your browser. Computation is executed entirely on your device. We do not store, view, or transmit your inputs over our network. Your computation remains on your personal machine.
Frequently Asked Questions
What is Julian Day 0?
Julian Day 0 began at noon on January 1, 4713 BC in the proleptic Julian calendar.
What is Modified Julian Day (MJD)?
MJD offsets JD by 2,400,000.5 days so days begin at midnight UTC instead of noon and numbers are more manageable.
Related Utilities
Frequently paired browser tools in Date & Time Tools