Julian Date Converter

A Julian Date (JD) is a continuous count of days since noon on January 1, 4713 B.C. (on the Julian calendar).

• It's widely used in astronomy and scientific calculations
• It simplifies calculating time intervals between dates
• The fractional part represents the time of day (0.5 = noon UTC)

The two calendars differ in how they handle leap years:

• The Julian calendar adds a leap year every 4 years
• The Gregorian calendar skips leap years in century years (e.g., 1900) unless divisible by 400 (e.g., 2000)
• The Gregorian calendar was adopted in October 1582 to correct drift in seasonal dates

The fractional part of a Julian Date represents the time of day in UTC:

• 0.0 = Previous day at noon UTC
• 0.5 = Midnight UTC (start of the day)
• 0.75 = 6:00 AM UTC
• 1.0 = Noon UTC

Julian Dates provide several advantages:

• Easy date arithmetic: Simply subtract two Julian Dates to find days between them
• Continuous time scale: No complications with months, years, or calendar changes
• Scientific standard: Widely used in astronomy and space mission planning

Common reference epochs include:

• J2000.0 = 2451545.0 (January 1, 2000, 12:00 UTC)
• Unix Epoch = 2440587.5 (January 1, 1970, 00:00 UTC)
• GPS Epoch = 2444244.5 (January 6, 1980, 00:00 UTC)