It's fun to talk about pi (π). I remember when Sr. Mary Gregory taught it to me when I was a wee lad and she was a wee slip of a nun. She said the symbol looked like a little hat or perhaps two little running legs. And as we all remember from when the good sisters taught us, pi is the mathematical constant that God put into all circles, everywhere and at all times. It's the ratio of a circle's circumference to its diameter, which we understand to be an irrational number equal to:

3.141592653589793238462643383279502884197169399375105820974944592307816406286…

The funny-looking Greek letter "π" has been used ever since the mid-18th century, when Leonhard Euler began to popularize it. In the past few decades, some of the geekier souls in Christendom have been celebrating March 14 (3/14) as "Pi Day." It's usually celebrated with… yes… a slice of pie.

And as the 2009 US Congress passed a bipartisan resolution designating March 14 as "Pi Day," it's practically a civil duty of all Americans, even those who avoid gluten, to indulge in said pie.

God bless America!

However, though Sr. Mary Gregory was knowledgeable about so many things, she forgot to mention that some mathematicians are up in arms over this little Greek symbol.

Apparently, many of them simply want to ditch the entire idea and use "τ" (tau) instead. Those mathematicians who like to tilt at this particular windmill are known, for the love of God, as "Tauists."

Apparently, those in the know, who really, really know what needs to be known, are quick to point out τ (which is 2π) is a much more accurate, and less confusing, way to measure circles. After all, π only refers to the distance between the center of a circle and its edge (i.e., its radius) while τ, on the other hand, measures the true diameter of the circle. The relevance of this becomes immediately obvious when one considers how many times one needs to know the diameter of a circle rather than its radius in everyday life.

Thus, instead of celebrating March 14 as "Pi Day," it's recommended that we celebrate June 28 (6/28) as "Tau Day."

And as we make our elaborate Tau Day celebration plans, we should also stop to consider the other tau which is significant to Christians.

The Tau Cross, (T) named after the Greek letter it resembles, is also known as St. Anthony's Cross, the Old Testament Cross, the Anticipatory Cross, the Advent Cross and the Franciscan Cross.

The letter tau or T has been used as a symbol of the cross since the earliest Greek New Testament texts. However, the symbol is even older than that. In fact, the tau is identified as the sign angels gave to the Prophet Ezekiel to mark the foreheads of those Jews who were saved:

"Go through the whole city of Jerusalem and put a mark on the forehead of everyone who is distressed and troubled because of all the disgusting things being done in the city." (Ezekiel 9:4)

There is also an additional Old Testament reference to the tau in that it looks like the outstretched hands of Moses as he witnessed the Israelites fighting the marauding Amalekites. (Exodus 17:11)

The tau is also the last letter of the Hebrew alphabet and in Proto-Sinaitic, the language from which Phoenician and Hebrew are derived, tau looked exactly like a cross we are commonly understand: "t". St. Jerome specifically pointed out that the mark was shaped like the last letter in the Hebrew alphabet in his writings.

This sign is mentioned again in Revelation 7, when one of the angels of the Apocalypse admonished his fellow seraphs to withhold punishing humanity until all believers have had their foreheads marked with God's sigil. (Revelation 7:3) In addition, it's also mentioned as adorning the foreheads of all those who live in the City of God. (Revelation 22:4) For this reason, St. Anthony of Egypt, drew the tau on his cloak.

The Tau Cross is most commonly associated these days with St. Francis of Assisi and his Franciscans, both religious and secular. In fact, Pope Innocent III, the pontiff who sanctioned the Franciscan Order, incorporated the tau symbol into his own crest after meeting St. Francis. It's not uncommon to see both kinds of Franciscans festooned with a wooden tau cross around their necks made from either olivewood or a Filipino hardwood known as nara.

St. Francis originally learned of the tau from the Antonians―a male religious community founded in AD 1095 whose ministry was caring for lepers. The Antonians would paint a large tau on their habits to imitate St. Anthony of Egypt.

Pope Innocent III was so taken with the tau cross that he opened the Fourth Lateran Council on November 11, 1215, with these words: "I have desired with great desire to eat this Passover with you." (Luke 22-15)

Innocent announced that for him and for the whole Church, the symbol they were to take as the sign of their Passover was the tau cross.

St. Francis of Assisi who was present at the Fourth Lateran Council, was very moved by the Pope's admonition especially when the pontiff ended his homily with "Be champions of the tau."

St. Francis used the tau to sign all documents. (FF 980) He even had the image painted on the walls and doors of places where he stayed. Both St. Bonaventure and Thomas of Celano wrote that Francis would trace the tau on himself before any proposed action (FF 1347) and constantly recommended it to his followers.

As Pi Day is celebrated by a slice of "pie," the only appropriate way to celebrate Tau Day is with…yes, you guessed it…two slices of pie.

And you might as well serve it à la mode…after all, Tau Day only comes but once a year and there are simply not enough reasons to indulge in sweets these days. And, as Christ reminds us, we should always proudly bear our tau and follow Him.

Get it?

Christ is the Tau/Tao/Way, the Truth and the Life and as Christians. We're the new "Tauists," who willingly inscribe the tau upon our minds, lips and hearts each time we hear the Gospel read at Mass or upon reverencing the Blessed Sacrament.

This year, on June 28, remember that it's yet another opportunity for us to dedicate our day specially to Him.

Happy Tau Day, everyone.