Fr Gareth explains how the moon guides our festivals, and the challenges of setting time, seasons and feast days around the world.
God said, “Let there be lights in the expanse of the heavens to separate the day from the night. And let them be for signs and for seasons.” (Genesis 1)
From ancient times human civilisations have marked the passage of time by noting the movements of the Sun and Moon. The regularity of our days, months, and years, are determined by the laws of physics.
When our Solar System was formed, it was a rotating disc of dust and gas, resembling the shape of a fried egg. Gravity causes most things in the universe to rotate: two objects might be pulled together, but when they miss each other, they can be drawn into an elliptical orbit. Those clumps of matter which were slightly more dense than the average started attracting more matter to come close, by their own gravity. And just as a twirling ice skater speeds up when she draws in her arms, so these lumps and clumps spun faster as the material fell inwards. In the fullness of time this formed the Solar System as we know it, where the Sun, the planets and their moons mostly rotate in the same direction, and in the same sense as everything orbits the Sun. There are exceptions: the planet Venus rotates exceptionally slowly and in the opposite direction, while the planet Uranus is tilted almost sideways. These are probably the results of collisions with planetary sized bodies in the Solar System’s youth.
Being a massive planet grants us great stability. Tiny changes in Earth’s mass, when a rocket is launched or a meteorite lands, are so small compared with the Earth itself that they cause negligible changes to Earth’s motion. But over billions of years, our day is slowing down and our Moon moving further away. This does result in a ‘leap second’ having to be added to our timekeeping occasionally, now that we have atomic clocks which can outperform our planet for accuracy.
Some cosmic bodies are nicely synchronised. Our Moon rotates on its own axis once each time it orbits the Earth, which is why we always see the same face. Some of the rings around Saturn are kept in trim by ‘shepherd moons’ on either side, which in a complex gravitational dance, sometimes switch places. But there are no neat matches between Earth’s rotation, its orbit around the Sun, and the time the Moon takes to circle the Earth. This means any human calendar is going to have rough edges which need compromises. There are some observable fixed points – the longest day of the year (solstice) and the day when the length of the daytime equals the length of the night (equinox). This allowed ancient civilisations to recognise the length of a year.
The Islamic calendar is strictly lunar; the start of a Muslim month, such as Ramadan, cannot be proclaimed until a new moon has actually been sighted. Jewish practice is more pragmatic and divides the year into months of 29 or 30 days which begin and end at approximately the time of the new moon. This requires a leap month every 2 or 3 years.
Catholics living in England and Wales will recognise four “New Years” – the civic new year on 1 January; the tax year, starting 6 April; the “School Year” which starts at the beginning of September; and the Liturgical Year which begins on the First Sunday of Advent (the Sunday closest to 30 November). Early Christian Britain used to keep New Year on the Feast of the Annunciation, 25 March; when England and Wales adopted the Gregorian Calendar in 1752, two weeks of dates were removed, and at the same time New Year’s Day was relocated to 1 January. The tax office wished to still count 52 weeks. Hence a tax year which began 25 March ended on 5 April and so our tax year indirectly honours the Incarnation!
The Jewish Calendar similarly has four new years: the ‘civic’ year begins in the Northern Autumn, on the first day of the Jewish month of Tishrei. But Tishrei is regarded as the seventh month of the year, and the religious year begins six months later, in the month of Nisan. Exodus 12 commands the keeping of the Passover on 15 Nisan (also called Aviv in Deuteronomy 16) which is to be “the first of months for you”. Exodus 23 commands the keeping of an autumn harvest festival in Tishrei which is the “departing of the year”; this is why the reigns of kings and the number of the civic year are incremented then and not in Nisan. There are two other New Years associated with tithing laws, the dates on which you go back to zero for counting newborn livestock, and fruits from the trees. So Jewish trees have their own New Year!
Calendars were of limited importance for the early Christian community: Colossians 2 advised believers to give little importance to whether or not a person kept the Sabbath or observed New Moon festivals. In those first generations there was some ambiguity about whether Christianity was a branch of Judaism or something separate. We know that at the end of the first century, certain Christians fasted on Wednesdays and Fridays to distinguish themselves from the contemporary Jewish custom of fasting on Mondays and Thursdays. The Jewish Sabbath lasted from sundown on Friday to sundown on Saturday; but Christians celebrated the Lord’s Day on Sunday.
When Christendom emerged from hiding and became the official religion of the Roman Empire in the 4th Century, the seven-day week was officially adopted for civic life. The original Roman Calendar had begun on the calends of March, making September the seventh month of the year. At some time, possibly in the year 153 BC, New Year’s Day was moved to the start of January. So the Christian calendar was based on the Roman one, and martyrs’ memorials noted according to the Roman months. But Christians were conscious that Christ had died at Passover, which was a significant Jewish festival, and there was a question mark over when churches should celebrate an Easter ceremony.
This question was solemnly debated in AD 325 at the Council of Nicea, the great gathering of the early church largely responsible for the longer Creed still said at Mass. The Council declared that Easter should be celebrated on “the Sunday following the first full moon after the spring equinox.”
In 2016, the Archbishop of Canterbury indicated that conversations were in progress between Anglican, Catholic, Coptic and Eastern Orthodox churches about setting a fixed date of Easter. The Catholic Church has no objection to Easter being on a fixed Sunday in April – but the major sticking point to reaching agreement is this ancient declaration by an Ecumenical Council, which many Orthodox Christians view as binding.
You might think the solution is easy – just keep following the rules given in 325. But it’s not so simple. Nowadays, neither the Catholic nor Orthodox churches follow this method precisely. The true equinox can happen on the day we call 19, 20 or 21 March. Historically, the churches have ignored this and just used the date of 21 March as the ‘official’ equinox. But the Orthodox Churches still use the Julian Calendar, without a leap year every fourth year, so the day they call 21 March, we currently call 3 April. This will slip three days later every four centuries, starting in the year 2100. If the Orthodox churches continue using their calendar for centuries to come, their Easter will slip through Northern summer and eventually into autumn – and Orthodox Christmas will be well into the northern Spring!
In 1997, a joint working party of church representatives met in Aleppo, Syria, and published a proposal. All churches could return to the rules published at Nicea, by using astronomical calculations to calculate the split-second timing of the first Full Moon after the mathematically precise spring equinox. But a further problem had to be resolved – when does the “following Sunday” begin? We have different time zones across planet Earth, so it could happen that at the calculated moment, in some easterly locations it would already be the small hours of Sunday, while in western places, it would only be Saturday. The Aleppo committee proposed that the calculation be applied to when it is Sunday in Jerusalem.
The New Testament does not command Christians to keep any particular festivals, but it does encourage followers of Jesus to avoid unnecessary disagreements (John 17; I Corinthians 1 & 3). While a fixed date in April would suit the secular world, this would offend the conscience of many Christian believers who feel bound by Nicea. Rather than offend the less flexible believers (Romans 14, I Corinthians 8), maybe all the world’s churches could adopt the Aleppo proposal. If we can achieve this, I look forward to celebrating Easter with you on 28 March 2038!
Revd Dr Gareth Leyshon is a parish priest in the South Wales Valleys, who read physics at Oxford and completed a doctorate at Cardiff (a study of the structure of distant galaxies) before entering seminary.
