Why is Sunday 4/13 Passover

But not Easter?

Easter and Passover are religious holidays, for Christians and Jews respectively. Their dates are not set by secular governments, but are tied to the seasons and the moon.

If you’re really an expert on this stuff, you’ll find things in here to quibble with. If not, take it as broadly true.

I want to wish a very happy and blessed Passover to Jews everywhere.

Easter

In my Catholic grammar school, we were taught the formula for Easter: it’s the first Sunday after the first full moon after the vernal equinox. I thought that was so cool that I’ve always remembered it. This is for Western Christianity. In Eastern Orthodox it can be different.

However, as the great architect Ludwig Mies van der Rohe said, “God is in the details.”

You can look up the origin of that quote, and it’s probably not really Mies.

Such nerdy details as “what if the vernal equinox is not March 21?” and “what if that Easter day is different depending on what time zone you’re in?” are covered here.

If you’re a programmer, note that this formula is a “greater than” and not a “greater than or equal to.” Thus,, 4/13 can’t be Easter because it’s a full moon today.

Passover

Easter is to commemorate Jesus’ rising from the dead, and that happened after the Jewish Passover. So logically, you would think it would always be one week after Passover, as it is in 2025. But you’d be wrong!

The formula for Passover is here. It is also tied to the moon and the season, but it’s set as the 15th day of Nisan, or Nissan. Nisan is a lunar month which begins on the new moon, so the 15th will always be a full moon.

There are many, many complications here, too. A strictly lunar calendar will not be aligned with the solar calendar that we use, so that, without adjustment, Passover would eventually be in the winter, which is strictly forbidden in the Bible. So they adjust for that, and also for leap years. It’s also changed over the millennia, and you can read about that in the above reference, too.

Can They Ever Be The Same?

Yes, they can, but it’s rare. Christians use the Julian calendar, which is not the same as the Hebrew calendar, and the official date of the equinox, March 21, is not always the real solar date.

So, to summarize: it’s complicated, but you can always look up at the moon after the equinox and figure out that it must be getting close.