I’ve just spent the weekend in Rome. In fact I had one of the best holidays ever running around the Italian capital and generally being silly with my friends. We also visited the Vatican, naturally, and so upon returning home I thought I should do a Roman Catholic Orbiting Frog post.

So what did the Pope ever do for Astronomy? Well quite a lot it seems. There is a Vatican Observatory outside of Rome which operated for many centuries. Its origins can be traced back to the 16th century and research is still done there today.

The observatory was first thought of by Pope Gregory XIII who had a penchant for astronomy. It is actually him that grabbed my attention when looking up the history of the papacy’s astronomical ties since Gregory himself enacted something which has since affected most of the world today.

A thousand years ago, give or take a century, the Roman Empire created the Roman Calendar. It consisted of ten months (Martius, Aprilis, Maius, Junius, Quntilis, Sextilis, September, October, November, and December) in a year of 304 days. After December had finished there would be a period of Winter in which there were no numbered days until the King decided it was time to start over, based on thr advice of his astronomers.

One king had the bright idea to insert a specific Winter and so introduced January and February, although February came first for over 200 years! Then in 46 Bc, another 400 years later, Julius Caesar formalised the calendar (remaning some Months along the way in the form of July and August) into what is called the Julian Calendar. This was a system of years with 365 days and then every fourth year (a leap year) 366.

By the time Caesar did this, the months and the season were no longer at all in sync. He had to add in 90 days to the year 46BC in order to resynchronise them. But even this new system - the height of technological innovation at the time - wasn’t quite right.

So it was that in 1582 AD, Pope Gregory XIII devised a way to sort the calednar out once and for all. What he came up with was a system based on a cycle of 400 years comprising 146,097 days, in a year of an average length of 365.2425 days. The Gregorian calendar, as it  became known, is a modification of the Julian calendar in which leap years are omitted in years divisible by 100 but not divisible by 400. By this rule, the year 1900 was not a leap year (1900 is divisible by 100 and not divisible by 400), but the year 2000 will be a leap year (2000 is divisible by 400).

Pope Gregory’s calendar was constructed to approximate the tropical year, which is the true time taken for the Earth to complete one orbit around the Sun.

The Julian calendar was switched over to the Gregorian starting in 1582, at which point the 10 day difference between the actual time of year and traditional time of year on which calendrical events occurred became intolerable for framers and the general life. Pope Gregory decreed that the day after October 4th 1582 would be October 15th, and so the Catholic countries of France, Spain, Portugal, and Italy complied.
The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by 11 days. England and what would become American finally followed suit in 1752, and Wednesday, September 2nd, 1752 was immediately followed by Thursday, September 14th This traumatic change resulted in widespread riots and the populace demanding “Give us the eleven days back!”, according to Vardi’s ‘The Gregorian Calendnar’.

Makes daylight savings seem like child’s play.