Left panel — Calendar → JD: Enter year, month, day, and UTC time, hit Convert (or press Enter). Outputs both the full Julian Date and Modified Julian Date (MJD = JD − 2,400,000.5). The Now button fills in the current UTC time instantly.

Right panel — JD → Calendar: Paste any JD or MJD value (entering one clears the other automatically). Outputs a human-readable calendar date and an ISO 8601 timestamp with copy buttons on all results.

Additional Formats panel appears after any conversion and shows Unix timestamp, Day of Year, Day of Week, Truncated JD (TJD), J2000.0 offset in days, and Besselian Year.

Reference Epochs — eight clickable presets including J2000.0, Unix Epoch, GPS Epoch, B1950.0, MJD Epoch, and Julian Day 0. Click any to load it straight into the JD→Calendar converter.

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