Context: Philip II of Spain decreed the change from the Julian to the Gregorian calendar, which affected much of Roman Catholic Europe, as Philip was at the time ruler over Spain and Portugal as well as much of Italy. In these territories, as well as in the Polish–Lithuanian Commonwealth (ruled by Anna Jagiellon) and in the Papal States, the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582. The Spanish and Portuguese colonies followed somewhat later de facto because of delay in communication.

Question: What ruler decreed the change to the Gregorian calendar?
Answer: Philip II of Spain

Question: Besides part of Italy, over what areas did Phillip rule?
Answer: Spain and Portugal

Question: What was the first day selected to be the first day using the new calendar?
Answer: Friday, 15 October 1582

Question: What was the last day the Julian calendar was used?
Answer: Thursday, 4 October 1582

Question: Why did the Spanish colonies lag behind in adopting the calendar?
Answer: delay in communication

Question: What King decreed the change from the Gregorian to the Julian calendar?
Answer: Unanswerable

Question: Who was affected by Philip II's switch to the Julian calendar?
Answer: Unanswerable

Question: What changed Julian Thursday, 4 October 1582 to Gregorian Friday, 15 October 1582?
Answer: Unanswerable

Question: What calendar was last used on Friday, October 15 1582?
Answer: Unanswerable