Easter Sunday is rather late this year on April 19. In some ways, the celebration is a strange one. Why does the holiest of Christian holidays bounce around the calendar? Why do small children search for eggs and worship a large rodent?

In fact, you can blame those Easter oddities on the moon. The date of Easter harkens back to the Jewish Passover (or, more correctly, Pesach) celebration. Both are celebrations of spring — when the world is reborn in a flurry of new life. They are both connected with the moon, which grows and then shrinks over the course of about a month. For one day each month, the moon disappears and then is reborn as a thin crescent.

In cultures around the world, the death and rebirth of the moon symbolize the death and rebirth that are necessary if we, and the planet we live on, are to be renewed.

The Jewish calendar is based on the moon and not the sun as our modern Gregorian calendar is. The number of lunar cycles in a year does not divide evenly into the solar year, so the Passover celebration begins on a different day each year. Generally speaking, Passover began on the evening of the first full moon after the vernal equinox, the first day of spring.

During the early days of Christianity, no one knew exactly when to celebrate Easter. To settle the matter, Constantine, the Christian Emperor of Rome, convened the Council of Nicaea in 325 A.D. The council decreed that Easter would happen every year on the Sunday following the first full moon after the vernal equinox. If the full moon happened on a Sunday, then Easter would be celebrated on the following Sunday. The council also ruled that Easter had to occur after the beginning of Passover.

Roman Catholic and Protestant churches eventually abandoned the Passover rule, even though the Christian Bible makes it quite clear that Jesus died and was reborn during Passover. The eastern churches did not, which is why the Eastern Orthodox Church sometimes doesn’t celebrate Easter on the same Sunday as other Christian churches.

If all of this seems complicated, please note that I have oversimplified it, as members of the Jewish and Eastern Orthodox communities will probably notice. The Eastern Orthodox Church uses the Roman Julian calendar, not our modern Gregorian calendar, to determine these dates, so sometimes the two Easters don’t occur on the same date for that reason as well.

This year, the intricacies of the Jewish lunar calendar determined that Purim, not Pesach, was celebrated March 20-21, the day of the vernal equinox. Pesach begins on the next full moon evening, April 19.

Our calendar difficulties all arise because of fundamental astronomical mismatches among our methods of determining time. The lunar cycle (i.e. the month) does not divide evenly into the year, the orbit of Earth around the sun. For heaven’s sake, the length of a day doesn’t divide evenly into either the month or the year. We must do the best we can with what God and/or nature gave us.

The moon also figures into the Anglo-American habit of celebrating Easter through the distribution of eggs to children.

When the early Catholic Church began to spread its religious beliefs in England, they realized that they could make their religion more palatable by incorporating some of the practices of the indigenous religions.

In those days, the English worshiped many gods. Among them was Ostara — Eostre to the Romans — the goddess of springtime. She made the warm weather come and the world burst forth with new life.

Near the first day of spring, when her powers were at their greatest, Eostre gathered little children around her and performed feats of magic. One fine spring day, as the children sat before her, a beautiful songbird landed on her outstretched finger. To the astonishment of the children, she transformed the bird into a rabbit.

The children squealed with delight until they saw that the rabbit was weeping — and with good reason. It had been a bird that could fly high above the clouds, safe from all harm. Now it was a rabbit, earthbound, prey to all the animals that love to eat bunnies for breakfast.

The children begged Eostre to change the rabbit back into a bird, but this she could not do. Instead, on the first day of spring, when her powers are at their greatest, she can transform bunny back to bird for a single day. On that day, the bird lays her eggs.

The next day, bird must become bunny again. However, she remembers the children who took pity on her. On that day, she delivers her eggs to all the children of the world.

On all other days, the rabbit lives on the moon, where she may still soar high above the clouds, safe from harm. If you look at the dark markings on the full moon, you can see the outline of the rabbit to this very day.

And that is why, on the highest day of the Christian calendar, the Eostre Bunny still delivers her eggs to the descendants of the children who took pity on her so long ago. If your family is like mine, you’ll almost surely find a few remnants of Eostre worship hanging around in your refrigerator.

But our springtime obsession with eggs and bunnies goes far deeper than that.

The egg is, after all, a symbol of new life. Out of it, as if by magic, springs a brand-new (and very cute) living, moving, breathing entity.

As for bunnies, they embody, shall we say, the intense the procreative proclivity of springtime. Get yourself a mating pair, and before you know it, you’ll be knee-deep in bunnies.

The egg symbolism associated with early spring has spawned some pretty strange beliefs and practices that continue to this day. Easter eggism is among the least weird of them.

In fact, astronerds like me view the spring as a time to ask profound questions. I can’t think of a greater issue than one that has perplexed humans since the dawn of human intelligence.

On or near the vernal equinox, can we balance an egg on its end?

Well, of course we can. Before you accuse your neighborhood astronomy columnist of being a hard-boiled propagator of scrambled mythological insanity, read on, skeptical reader.

Earth orbits the sun once a year. We have seasons in the first place because our planet’s axis of rotation is tilted about 23 degrees with respect to the path of its orbit.

On the summer solstice, the first day of summer, the northern part of Earth’s axis is pointed toward the sun. As a result, the northern hemisphere leans in toward the sun. The sun’s rays hit our hemisphere more directly, from straight above us, so to speak.

By contrast, on the first day of winter, the winter solstice, our hemisphere is pointed away from the sun. The sun’s rays hit us at a more glancing angle, and colder weather results. The entire process is reversed for the southern hemisphere, of course.

The vernal equinox happens halfway between the two solstices. Earth’s axis is pointed perpendicularly to the sun. Egg balancing aficionados believe that the tilt of the axis somehow balances out the sun’s gravity, and ovoid madness sweeps the planet.

Similar astronomical conditions exist at the autumnal equinox, of course. However, the first day of fall apparently doesn’t generate the same eggy enthusiasm as the vernal variety.

Any astronerd will tell you that vernal egg magic is a bunch of hoo-ha. Earth spins on its axis. Your gravitational orientation with the sun is constantly changing. Also, the moon exerts far more gravitational force on planet Earth, and it’s up there moving around like crazy according to a completely different cycle than Earth’s revolution around the sun.

Here’s the hard-boiled truth. Eggs are problematic to balance for two reasons. They must rest on a single point on their surface. It’s simply difficult for the amateur ovum balancer to find the eggs-act gravitational centerline of the ovoid. Also, the yolk of an egg is much denser than the clear part, and the yolk often sits high in the egg. The high center of gravity makes the egg want to fall over. Try balancing an ice pick and you’ll see what I mean.

Still, with a little patience, you should be able to balance an egg next March 21. In fact, you should be able to do it on any day of the year if you know the tricks of the trade.

The main trick, which I have poached from various old magic books, is to try a whole mess of eggs. Eventually, you’ll find one that balances better than the rest.

Then take a careful look at the “magic” egg. You’ll see little bumps on the bottom in just the right places help the egg stand upright.

You can significantly increase your apparent ability by shaking the egg vigorously before you start. You’ll spread the yolk out within the egg and lower its center of gravity, making egg balancing a relative breeze. (Hold the egg firmly but not too tightly. You don’t want to get egg on your face.)

Don’t follow the common advice and use a leftover, hard-boiled Easter egg. It spoils the springtime magic if you can’t crack the egg after you’ve performed the trick.

Old myths die hard. If you know people who still believe in the gravitational magic of the vernal equinox, tell them that the yolks on them.