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Convert between Gregorian calendar dates and astronomical Julian Day Numbers
Free online tool for astronomers, historians, and date calculations
Interactive Julian Day conversion tool will appear here
Julian Day Number (JD): A continuous count of days from the beginning of the Julian Period on January 1, 4713 BCE in the proleptic Julian calendar. It's used primarily by astronomers and historians for calculations spanning long periods.
Key Features: Julian Day Numbers eliminate the complexity of different calendar systems, leap years, and varying month lengths. Each day gets a unique sequential number, making date calculations straightforward.
Usage: Essential for astronomical calculations, historical dating, software development, and any application requiring precise date arithmetic across different calendar systems.
A: Julian Day Numbers start from January 1, 4713 BCE (proleptic Julian calendar), which equals JD 0. This date was chosen to predate most historical events.
A: The decimal part represents the fraction of a day (time). JD 0.0 is noon UTC, JD 0.5 is midnight UTC. This allows precise time representation.
A: Our converter uses the standard astronomical algorithm and is accurate for all dates in the Gregorian calendar (1582 CE onwards) and earlier dates using the proleptic Gregorian calendar.
Algorithm: This converter uses the standard astronomical algorithm for Julian Day calculations, accounting for the Gregorian calendar reform of 1582.
Precision: Results are calculated to 6 decimal places, providing accuracy to fractions of seconds for time calculations.
Date Range: Supports all dates from ancient times to far future dates, with automatic handling of leap years and calendar reforms.
Standards: Follows IAU (International Astronomical Union) standards for Julian Day Number calculations.