Julian and Maya Day Numbers

In 1582, Joseph Scalinger devised the Julian Period, from which Julian Day Numbers (JDN) derive. It was named after his father Julius, not the Julian calendar. It essentially numbers each day since January 1, 4713 BC, in the Julian calendar. Scalinger starts each day at noon, so each Julian Day Number starts 12 hours after the Gregorian and Julian dates shown.

Julian Day Numbers are used because calculating the number of days between two dates across several years using the Gregorian or Julian calendars is difficult. It is easier to perform such operation if you compare the JDNs of the two dates.

The Maya Day Number is a similar idea to the Julian Day Number. The Maya Day Number is the number of days since the zero date of the Maya Long Count.