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Astral Atlas
Wiki concept · Time & location

Julian date

Also called Julian day · JD · jd_tt · jd_ut1

A continuous astronomical day count with fractions for time of day. The accompanying time scale must be stated.

In this entry

Word origin · etymology

Historical astronomical name.

The day count derives from Scaliger's Julian Period, named for its Julian-calendar years; it is not simply a date written in that calendar.

US Naval Observatory: Calendars, Explanatory Supplement ↗

How we know · epistemology

Counting convention

A continuous day count makes time arithmetic reproducible. The number needs an accompanying time scale and day-boundary convention; it is not itself evidence for a historical calendar identification.

US Naval Observatory: Julian dates ↗

Connected concepts

These links connect subjects and terminology. They do not establish a shared historical origin.

Sources & provenance

Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.

Find these sources across the wiki →

  1. US Naval Observatory: Julian dates ↗
  2. US Naval Observatory: Calendars, Explanatory Supplement ↗