1. In the summer of 1572, he entertained one last important guest, Pope Gregory XIII.

2. Annunciation New Year Marches Along In 1582, along came Pope Gregory XIII who reformed the calendar

3. Lilio's brother Antonio presented the manuscript to Pope Gregory XIII; it was passed to the calendar reform commission in 1575.

4. 25 In 1582 Pope Gregory XIII established the Gregorian calendar, which most of the world now observes, to account for an equinox inconvenience.