Astronomical
Julian Day Number
Astronomers' continuous day count · itself a running clock
Astronomers’ running tally of days since noon on 1 January 4713 BCE (Julian) — one continuous number that sidesteps every calendar’s months and leap rules, ideal for measuring intervals.
—
In UTC at 02:02 on October 27, 2026, this calendar read 2461340.58481. The reading above is live, in your own time zone.
At a glance
- Type
- A continuous count of days
- Origin
- Built on Joseph Scaliger’s Julian Period of 1583; astronomers’ day count since the 19th century
- Day
- Begins at noon, Universal Time — the astronomers’ convention
- Counts from
- Noon on 1 January 4713 BCE, in the Julian calendar
- Where it’s used
- Astronomy and software, for measuring the time between dates
- How it’s worked out here
- Exact arithmetic from your device’s clock
Does something here look wrong? Tell us about the Julian Day Number calendar.