Julian Day
About the Julian Day
Astronomers count days continuously as Julian Day Numbers from noon Universal Time on 1 January 4713 BCE in the proleptic Julian calendar. Joseph Scaliger proposed the 7980-year Julian Period in 1583 as the product of the 28-year solar, 19-year lunar and 15-year indiction cycles, and John Herschel popularised day counts in 1849. The Modified Julian Date subtracts 2,400,000.5.
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