Date of Easter

Happy Easter! Now, why is an astronomy newsletter sending you Easter wishes? The easy answer is that the whole several weeks beginning with Ash Wednesday, culminating with Easter Sunday, is based on the calendar.

Easter is always celebrated on the first Sunday after the first Full Moon after the first day of spring. But, there happened to be a problem with that day in the 16th century. Apparently, in 325, the First Council of Nicaea determined that Easter be associated with both the Moon and the start of spring; but, in the late 1500s, that association was occurring early in the month of March.

Julius Caesar introduced a calendar in 46 B.C. that contained 365 days for three years, and a 366th every fourth, giving an average year 365.25 days. Unfortunately, the Sun isn’t this cooperative: Its actual time line is several minutes shorter than that, resulting in a gain of about three days’ time every four centuries. As a result of that, by 1582, spring was starting the second week of March, closer to the 10th.

To revert back to the proper designated time of Easter, in 1582, October 10th was immediately followed by October 21st. Also, the leap years were changed slightly, in that an extra day would not occur on hundred years not divisible by 400. As an example, 2000 was a leap year; 2100 will not be. This restored March 21st as the first day of spring, and placed Easter where it belonged.

You might imagine, this did not fare well for the masses. Many people lost their birthdays that year, and landlords complained of losing rent. It also only began in the countries that treated the Pope as a major leader. Therefore, there were many parts of the world that stalled in this calendar change, including Great Britain and America, which waited until 1752, when the calendar then had to be revised by 11 days. This actually became a “Believe It or Not” section, where our first president, George Washington, was not born on the day we celebrate, February 22nd, but February 11th. The last country to adapt this calendar was Greece, which did so in 1923.

This year, the first Full Moon after the vernal equinox – the first day of spring – is Tuesday, April 15th, making Easter Sunday, April 20th. However, fortunately for us, in addition to celebrating this annual event, we have something else to look forward to, as this Full Moon is also bringing with it the ability to witness a total lunar eclipse. Happy Easter and Eclipse Watching to all.