Today (as I write, Friday, May 3, 2013), Orthodox Christians worldwide are observing Good Friday (or Holy Friday) — the Friday immediately prior to Easter Sunday.

Christianity, like other religions, subdivides into a number of major branches. Catholics are the single largest such major branch or subdivision within Christianity, accounting for about 50% of the total global Christian populace. The second largest major branch is that of the Protestants (who themselves are very diverse, ranging from mainline denominations to non-denominational evangelicals), accounting for around 37% of Christians worldwide.

The third largest such major branch, accounting for some 12% of the Christian populace, is the Orthodox branch, sometimes also known as Eastern Orthodoxy. The Eastern church broke apart from the Western (Catholic) church over a number of theological and other differences in a divisive split referred to as “the Great Schism” way back in the 11th century. Today, Orthodox (or Eastern Orthodox) churches are organized largely along national lines: the Russian Orthodox Church, the Greek Orthodox Church, the Romanian Orthodox Church, and a number of others.

Most Eastern Orthodox churches traditionally use a different sort of calendar than the Western or “Gregorian” calendar widely employed today by most Catholics and Protestants. This alternate way of calculating and counting the months, known as the “Julian” calendar, has the effect of determining dates for holidays which differ from their corresponding dates on the Gregorian or Western calendar.

So, whereas the Gregorian or Western calendar for 2013 has Easter falling upon Sunday, March 31, the Julian or Eastern calendar for 2013 has Easter instead falling upon Sunday, May 5.

And that means that whereas Good Friday for Catholics and Protestants was Friday, March 29, Good Friday for Eastern Orthodoxy is Friday, May 3.

In other words, today.

Regardless of its precise date, Good Friday commemorates the crucifixion and death of Jesus Christ, traditionally believed to have occurred on a Friday, just as Easter Sunday commemorates the resurrection which Christians (be they Catholic, Protestant, or Orthodox) believe subsequently occurred on the following Sunday.

The precise year in which the crucifixion and death of Jesus occurred is uncertain, but is estimated by many to have been circa 33 AD (or 33 CE).

The traditional Christian religious view is that Jesus Christ, understood by Christians to be the Son of God and a divine Savior, voluntarily died a self-sacrificial death in order to pay for, or atone for, all human sin. The New Testament gospel accounts paint a picture of Jerusalem’s Jewish leaders sentencing Jesus to death for the religious crime of blasphemy (for claiming to be divine).

Secular historians, by contrast, tend instead to view Jesus’s execution primarily as inflicted upon him by Jerusalem’s Roman overlords for the capital political crimes of treason and sedition. Death by crucifixion was Rome’s standard, and deliberately tortuous and humiliating, means of ridding itself of (and making examples of) troublesome political enemies and potential rabble-rousers — which is essentially how the Roman authorities viewed Jesus.

Christians observe Good Friday in various ways, which may include fasting, repentance, reflection, prayer, and special church services and liturgies.