Because we have the Internet, we can always lookup what days Easter and Passover fall. But since I like to know how things work, I wanted to figure out whether Easter will be in March or April. Also, when I used to create the schedule for the McCarren Softball league, I wanted to figure out whether I had to schedule a holiday for Easter weekend or for someone’s Seder.

There’s Holidays and Then There’s Holidays…

As far as I can tell, there are three kinds of holidays that we observe in the United States. Although most of this information is well-known, I’m posting it should this blog survive the fall of the American Empire and of Google.

First, there are those that fall on the same day of the year every year. Those would include New Year’s Day (January 1), Independence Day (July 4), Christmas Day (December 25), Valentine’s Day (February 14), May Day (May 1), St. Patrick’s Day (March 17), and Cinco de Mayo (5 of May). Those last two are fun, not only because those are both days of intemperance, but because they always fall on the same day of week as each other. Yes, really!

Second, there are those holidays that fall on a certain day of the week of a specific month. For example, Memorial Day is always on the last Monday of May as Labor Day is always on the first Monday in September. We do the same thing with other federal holidays, such as President’s Day (third Monday of February) and Martin Luther King Day (third Monday of January). The only exception to this Monday thing, of course, is Thanksgiving, which is on the fourth Thursday of November, not the last one as is commonly believed. Retailers love it when November has five Thursdays because it extends the holiday shopping season.

Third, there are the kinds of holidays that require the help of celestial bodies. The start of each season is not on the same day as last year, although it’s pretty close. The start of the northern-hemisphere spring is on the vernal equinox, around March 21, as the northern autumn starts on the autumnal equinox, also around September 21. But it’s never the same day because the seasons are a function of our planet’s orbit around the sun. When it reaches a certain point in that orbit, a new season has started. Our calendar doesn’t measure this exactly, but it’s pretty darn close.

Sheer Lunacy

Once you figure out the March equinox, you can start to figure out Easter and Passover, but you’ll need to figure out when you’ll see the next Paschal full moon. You have some options:

1. Look at the sky each night after the beginning of spring. Is there a full moon?
2. Look at a calendar. The Mexican food place down the street always gives me a calendar with the phases of the moon on it. I can check when I’ll see the first full moon of the spring.
3. Internet.

With this information, you can determine that Passover begins on the first day before this full moon. The Seder will be on the evening of this first full moon.

Easter is trickier because the Paschal moon is calculated from a table, not the moon itself. This is presumably because the full moon might appear different, depending on your position on Earth. Either way, Easter is the first Sunday after this full moon. If the Paschal Moon falls on a Sunday, we wait a week.

As complex as this sounds, Easter and Passover are always in the spring and the moon above will be waning during your Seder or Easter egg hunt.