As you have most certainly noticed by now, Easter Sunday does not fall on the same day each year. This is because it is connected with the Passover, (which is Holy Thursday), and that is based upon the lunar cycle. This method of reckoning important religious days goes back to ancient times.

But did you know that the calendar we use now is different than that in times past? Not by a lot… but it was enough to make ten whole days "disappear", in a sense, back in 1582. Here’s how…

For centuries, the world kept time according to the Julian calendar, with a year consisting of 365.25 days. The extra 6 hours at the end of each year was to try to keep the calendar in sync with the solar and lunar cycles. This quarter day builds up every four years into an extra full day, hence leap year.

Unfortunately, a tidy 6 hours was just slightly too much time. Since a year by definition is supposed to keep in time with celestial orbits, that technically makes it about 365.2422 days (slightly shorter than the extra 6 hours).

What difference does such a short amount of time make? Not much - at first. But over time, centuries in fact, the calendar gradually grew out of sync with the cycles of the sun and moon.

Thus it was, by the late 16th Century, that the Church noticed how significantly the calendar was out of line with the seasons. Experts on the matter observed that, by then, the extra time had so accumulated that the calendar was off by 10 days! Among many other things, this offset the calculation for when to properly celebrate the solemn feast of Easter.

So, in the year 1582, Pope Gregory XIII decreed the use of a new calendar that was much more accurate. To this day, the Gregorian Calendar is still in use throughout most of the world, and is considered the universal civil calendar.

In order to put the new calendar in effect, the year 1582 "lost" 10 days in October. The dates of the 5th through the 14th "vanished" to get the rest of the calendar on track. Thus, the day after October 4th was October 15th.

As God’s Providence would have it, this singular time would be uniquely memorable in Church history by an event more precious, if less global-impacting, than changing from the Julian Calendar.

St. Teresa of Avila, reformer of the Carmelites, had finished her work on Earth, and God called her home to Heaven. It was the very day the calendar changed, very early on October 15th, 1582, just following October 4th.