Julian Date Converter
Calendar notes
Blog
Practical guides for understanding Julian dates, historical calendars, and safer date conversion workflows.
Use these articles when a converter result needs more context: the difference between Julian Date and Julian calendar dates, why reform dates matter, how astronomers use day numbers, and what assumptions to record when normalizing historical sources.
Each guide is written to support the converter pages with plain-language explanations, reproducible assumptions, and cautions for research, archival, astronomy, and everyday date-conversion work.
What Is a Julian Date?
A practical guide to the two common meanings of Julian date and why the distinction matters when converting dates.
Read articleJulian Calendar vs. Gregorian Calendar
How the two calendars drift apart, why countries adopted reforms at different times, and what that means for historical dates.
Read articleWhy Astronomers Use Julian Day Numbers
Julian Day Numbers make date arithmetic predictable across long timespans, calendar reforms, and historical calendar systems.
Read articleAvoiding Mistakes in Historical Date Conversion
The common traps: local reform dates, old-style year starts, time-of-day assumptions, and ambiguous source labels.
Read articleJulian Date vs. Day of Year
Why a Julian Date, a Julian Day Number, and a three-digit day-of-year code are not the same thing.
Read articleHow to Convert Julian Calendar Dates
A practical workflow for converting Julian calendar dates to Gregorian dates without confusing them with Julian Day Numbers.
Read articleUsing Julian Day Numbers for Date Differences
How continuous day numbers make elapsed-day calculations clearer across calendars and long date ranges.
Read articleCalendar Conversion for Genealogy Records
How to handle old-style dates, local calendar reforms, and source notes when converting family-history records.
Read articleLunisolar Calendar Conversion Basics
Why leap months, local calendar variants, and civil-day assumptions matter when converting lunisolar dates.
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