Home > Calendar, Concepts, Ephemeris Program > Ephemeris: 02/27/2024 – Thursday is the Intercalary Day

Ephemeris: 02/27/2024 – Thursday is the Intercalary Day

February 27, 2024

This is Bob Moler with Ephemeris for Tuesday, February 27th. Today the Sun will be up for 11 hours and 2 minutes, setting at 6:27, and it will rise tomorrow at 7:22. The Moon, 3 days past full, will rise at 9:47 this evening.

Thursday we’re going to have one of those special days that only occur once every 4 years making this a leap year. It’s the intercalary day that compensates for that fact that the Earth takes 365 and a bit short of a quarter day to orbit the sun. That orbit is a year, and those quarter days are accumulated and added as the last day of February in years divisible by 4. The Gregorian reform makes a slight adjustment to most century years, making century years not divisible by 400 ordinary years to keep the calendar in sync with the seasons. The Romans, from who we’ve gotten our calendar considered the month of February as unlucky, and so they shortened it most years to 28 days. Enjoy your extra day Thursday.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –5 hours). They may be different for your location.

Addendum

Julius Caesar statue
Our current calendar system is taken from the Roman calendar reform that began in 46 BCE under the reign of Julius Caesar. Up to that time calendar keeping in the Roman Empire was rather haphazard. They started with a lunar calendar and things got so bad that they were about two months out of sync with the seasons. Julius Caesar’s calendar reform begin by making the adjustment in 46 BCE by making that year 445 days long. From then on the year was supposed to be 365 and a quarter days long, which was supposed to be adjusted by adding an extra day every four years. However, that wasn’t regularly done till about 8 CE under Caesar Augustus. That’s how things stood until 1582. Uncredited photo via Worldatlas.com.
Pope Gregory XIII painting by Bartolomeo Passarotti (1529–1592)
Pope Gregory XIII painting by Bartolomeo Passarotti (1529–1592).
No calendar is perfect. The average year of the Julian Calendar is 11 minutes and 14 seconds longer than the actual seasonal year which it is trying to model. By the time of the papacy of Pope Gregory XIII from 1572 to 1585 CE the error in the Julian calendar versus the actual seasons had grown to 10 days since the Julian Calendar was established 16 centuries before. The reason the Church was concerned was that Easter was slowly advancing toward summer, and Easter is a more important feast than Christmas, but is related to the Jewish Feast of Passover. I’ll discuss the formula for determining Easter as we get closer to it. However, the Gregorian calendar reform came in two parts: Ten days were dropped from the calendar between October 4th and 15th in the year 1582 and after that the every four year leap day rule, that is years evenly divided by 4, was modified so that on century years, that is years ending in 00, but not divisible by 400, became ordinary years, that is no leap days, this will keep the calendar in sync with the seasons for several millennia. This calendar reform occurring after the Reformation meant that only the Catholic countries adopted it. It took almost until the present day for everyone to adopt it. For ecclesiastical purposes the Orthodox Churches still used the Julian Calendar.
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