<P> The Gregorian calendar was introduced as a refinement of the Julian calendar in 1582 , and is today in worldwide use as the de facto calendar for secular purposes . </P>
<P> The Gregorian calendar was introduced as a refinement of the Julian calendar in 1582 , and is today in worldwide use as the de facto calendar for secular purposes . </P>
who came up with the modern day calendar
who came up with the modern day calendar
1582
1582