Josephus Justus Scaliger invented the Julian calendar (Julian day) still used in astronomy and called it “Julian” after his father: Julius Scaliger; it is a cycle of 7980 years without leap years or added or removed days; it begins at 12 AM on January 1, 4713 BC 7980 = 28 x 19 x 15 where: 28 is the solar calendar cycle (after 28 years the calendar repeats), 19 is the lunar Metonic cycle and 15 is the cycle of the Roman Indiction (a cycle linked to the medieval tradition)
