#tropicalyear — Public Fediverse posts

In 1900, Maksim Trpković revised the #JulianCalendar. Under his system, an year that yields a remainder of 0 or 400 when divided by 900 is a #LeapYear.

Milutin Milanković slightly altered this in 1923, changing the rule to years that give a remainder of 200 or 600. A mean year in this calendar is just 2 seconds off the #TropicalYear. It is used by some, but not all, #EasternOrthodox churches.

In the 17th century, #IsaacNewton recognised that the #julianCalendar was deficient but the #GregorianCalendar was too #Catholic for him. He worked on a new calendar whose mean year was just a few seconds shorter than the #TropicalYear (the mean Gregorian year is about 29 seconds longer). Newton viewed this as a feature rather than a bug, because under his system, the dates of the solstices and equinoxes would gradually drift back to those when #Jesus was alive.

But, as we now know, the #JulianCalendar's mean year is about 11 minutes 15 seconds longer than the #TropicalYear, and by the 4th century AD, the dates of the #solstices and #equinoxes had drifted from their official dates by several days.

In the 16th century, #Pope Gregory XIII used his authority as #PontifexMaximus to reform the calendar again, because that is something #popes can do.