Definition
A date format that expresses a calendar date as the day-of-year number (001 through 365, or 366 in a leap year), often combined with the last digits of the year. For example, 15 January 2024 is Julian date 24015 — the 15th day of 2024. The FAA uses this format on the margins of charts and publications to identify the print or revision date.
Plain English
A way of writing a date by counting how many days into the year it is, instead of using the month and day. So 1 February becomes day 032 — the 32nd day of the year.
Context Anchor
Seen in FAA handbook margin or revision identification, where it helps show the issue date of a page or change.
Derivation
Named after Julius Caesar, whose Julian calendar reform in 46 BC introduced the system of fixed-length years that this day-counting method is built on. Knowing the name has no Roman astronomy mystery behind it makes the format feel less intimidating — it’s just a sequential day count within a year.
Why Pilots Care
When checking that a chart or publication is current, the margin date is often given in Julian format. Misreading it can lead to flying with outdated information.
Intuition Check
Do not read julian-date as a special flight date or as the usual month/day format. Here it means “the numbered day of the year” used as a publication date code.
Example Sentence 1
The chart’s margin showed a Julian date of 24105, meaning it was printed on the 105th day of 2024.
Example Sentence 2
Flight logs often list the departure using the Julian date to keep records compact and sequential.