We have had rather a feast of eclipses recently. And there is more to come - six lunar months later this year, on September 28, there is another total eclipse of the moon. The Easter lunar eclipse we saw on Saturday night was bright and clear and not altogether unusual. You can expect to see one at least every 18 years and 10 and days when the sun and moon are both back in the same orbital positions relative to planet Earth. This is the so-called Saros period which was known to the Babylonians as the repeat cycle for eclipses.
There is a clay tablet found in the ruins of Babylon and now lodged in the British Museum, the so-called Saros Tablet, that records the 18-year cycle of eclipses over a period of 500 years, listing the incumbent Kings of Babylon at the time of each eclipse. The list includes Nebuchadnezzar, Cyrus the Great, Darius the Great and Xerxes the Great, down to the last kings of Babylon in the 1st century BC.
Two weeks ago the Herald highlighted the extreme 14m high tides along the Normandy coast of France that submerged the causeway connecting Mont St Michel to the mainland. This is not the result of climate change and rising sea levels but is part of the same 18-year Saros cycle known to the Babylonians.
The previous day, March 20, there was a total eclipse of the sun and it was this alignment of sun and moon that led to the exceptionally high tides which will repeat in 18 years when they are again in the same location relative to Earth. Interestingly, because of that extra one third of a day noted above in the exact Saros period, the next solar eclipse in the cycle will not be seen in the same location but roughly one third of the way further around the globe. It will take three Saros periods, 54 years and 31 days, before the sun is eclipsed again at more or less the same location on Earth. This cycle was also known to the ancients and is referred to as an Exeligmos period - when sun, moon and Earth are all again in the same position. These are the "fixed laws of the heavens" referred to in several books of the Bible.
For the early Christian church, Easter was linked to the Jewish feast of Passover which occurred on the 14th day of the first month in the ancient Jewish calendar. It was precisely the first full moon after the Spring equinox and commemorated the night of the departure of the Israelite tribes from slavery in Egypt. Full moon is the only time lunar eclipses can be observed and so from time to time these eclipses coincide with the Jewish Passover.
We are told in the Bible, and also in the Jewish Talmud, that Jesus was crucified on the eve of the Passover - a Friday. Luke's gospel states that John the Baptist began teaching and baptising in the 15th year of Tiberius Caesar which would be AD29. Jesus began his own ministry later the same year and several sources indicate a 3 year teaching ministry so this takes us to his crucifixion at the Passover in AD33. Astronomically, we find the date was 3 April AD33 in our current Gregorian calendar and the only possible date that matches all the historical and astronomical elements.
That evening of the crucifixion, when each household looked for the rising of the full moon so as to start their family Passover feast, the moon rose blood red in eclipse at 6pm. The apostle Peter referred to this seven weeks later when he stated the sun was "darkened and the moon turned to blood". Later that century a Greek writer by the name of Phlegon referred to these events stating that they occurred in the fourth year of the 202nd Olympiad. The first year of the first Olympiad began in the summer of 776BC so Phlegon's date is the spring of AD33 - a perfect match with the astronomical date. All this goes to show the historical accuracy of the Biblical account, a theme which can be repeated again and again.
Last weekend, 110 Saros periods later, we experienced our own Easter eclipse. Interestingly, Good Friday this year was the very same date, April 3.
• Dr Jeff Tallon is a physicist working in the field of superconductivity.