To unambiguously specify the date, dual dating or Old Style (O.S.) and New Style (N.S.) are sometimes used with dates. Dual dating uses two consecutive years because of differences in the starting date of the year, or includes both the Julian and Gregorian dates. Old Style and New Style (N.S.) indicate either whether the start of the Julian year has been adjusted to start on 1 January (N.S.) even though documents written at the time use a different start of year (O.S.), or whether a date conforms to the Julian calendar (O.S.) rather than the Gregorian (N.S.). 

The Gregorian calendar was a reform of the Julian calendar instituted in 1582 by Pope Gregory XIII, after whom the calendar was named, by papal bull Inter gravissimas dated 24 February 1582. The motivation for the adjustment was to bring the date for the celebration of Easter to the time of year in which it was celebrated when it was introduced by the early Church. Although a recommendation of the First Council of Nicaea in 325 specified that all Christians should celebrate Easter on the same day, it took almost five centuries before virtually all Christians achieved that objective by adopting the rules of the Church of Alexandria (see Easter for the issues which arose). QUESTIONS:

Q1:
1. Where does the Gregorian calendar come from?
2. What are the origins of the Gregorian Calendar?
3. 
Q2:
1. Who decided to make the Gregorian calendar?
2. Whose idea was it to put the Gregorian calendar into practice?
3. 
Q3:
1. Did Pope Francis create the Gregorian calendar?
2. Was it Pope Francis that came up with the Gregorian calendar?
3. 
Q4:
1. Which pope can up with the Gregorian calendar?
2. What was the name of the pope that created the Gregorian calendar?
3. 
Q5:
1. Does the work Gregorian come from Pope Gregory XIII?
2. Is the term Gregorian derived from Pope Gregory XIII?
3. 
Q6:
1. Was the Gregorian calendar created in the 16th century?
2. Did the Gregorian calendar come about during the 1500s?
3. 
Q7:
1. On what exact date was the Gregorian calendar first introduced?
2. When precisely did the Gregorian calendar come into existence?
3. 
Q8:
1. Was the Gregorian calendar made because of Christmas?
2. Did Christmas bring about the creation of the Gregorian Calendar?
3. 
Q9:
1. What celebration was at the root of the Gregorian calendar?
2. What holiday brought about the creation of the Gregorian calendar?
3. 
Q10:
1. Why was Easter important to the Gregorian calendar?
2. What about Easter made the creation of the Gregorian calendar important?
3. 
