The Astronomy of Easter
- Jay Ryan
- Updated Aug 27, 2024
Most Christians know that Jesus was crucified in Jerusalem at the time of the Passover, and in this way became the perfect Passover sacrifice, "the Lamb of God which taketh away the sin of the world" (John 1:29). Since the early centuries of the church, Christians have honored the death and resurrection of Jesus in the celebration of Easter. And while the observance of Easter has changed over the centuries, it is based on the Hebrew Passover.
Hebrew Roots
We read in the Book of Exodus how the LORD used Moses lead the Israelites out of Egypt. In Exodus 12, the LORD sent the final plague, smiting the firstborn of all Egypt. The Israelites were saved by sacrificing a lamb and covering their doorframes with its blood, so that the LORD would "pass over" the house and not smite the firstborn of Israel. And the LORD commanded that the Israelites remember the Passover in a seven-day feast....
"And this day shall be unto you a memorial; and ye shall keep it a feast to the LORD throughout your generations; ye shall keep it a feast by an ordinance for ever." - Exodus 12:14.
The LORD instructed Israel as to when the Passover should be kept: "In the first month, on the 14th day of the month at even, ye shall eat unleavened bread, until the one and 20th day of the month at even." - Exodus 12:18.
In the lunar calendar, the New Moon is the first day of the new month. The Full Moon is at mid-month, the 14th day of the month. So Israel was instructed to celebrate the Passover on the Full Moon of the first month. The LORD even tells us the name of the month....
"Observe the month of Abib, and keep the passover unto the LORD thy God: for in the month of Abib the LORD thy God brought thee forth out of Egypt by night." -Deuteronomy 16:1
The word "Abib" means "sprouting" or "budding" and is the first month of Spring, falling among our months of March and April. Abib is the only month of the year named by God in the books of Moses.
The Bible doesn't clearly indicate the calendar method used to keep track of Passover and other Hebrew holidays. However, for centuries the Jewish calendar has been based on the well-known, 19-year cycle of the Sun and Moon. God in His providence established that 235 cycles of the Moon's phases is nearly equal to 19 solar years. This means that every 19 years, the Moon's phases will recur on the same dates of the solar year.
This 19-year "luni-solar" cycle was the basis for the calendar used in Babylon. In the west, its discovery is attributed to the Greek philosopher Meton, who may have learned it from the Babylonians. The 19-year cycle was generally well known and understood in antiquity, and was apparently used by the Persian rulers of Babylon after the restoration of Israel.
It appears that the modern Jewish calendar was directly influenced by the Babylonian calendar. In addition to using the 19-year cycle, the modern Jewish calendar uses months with names nearly identical to the Babylonian names. In the books of Nehemia, Ezra and Esther (which record events after the Babylonian exile) you can find the month names "Sivan," "Elui," and "Adar," nearly the same as their Babylonian counterparts.
Most notable is the month "Nisan," the first month of Spring, corresponding to the Mosaic month of "Abib." In the modern Jewish calendar, Passover occurs on the fourteenth day of Nisan. The Jewish historian Flavius Josephus, writing in about 90 A.D., gives us an astronomical reference for the month of Nisan....
"In the month of Xanthicus, which is by us called "Nisan," and is the beginning of our year, on the 14th day of the lunar month, when the Sun is in Aries (for in this month it was that we were delivered from bondage under the Egyptians, the law ordained that we should every year slay the sacrific which I before told you we slew when we came out of Egypt, and which was called the Passover....)"
In the time of Josephus, the Sun was in the constellation Aries at the time of the Vernal Equinox, the first day of Spring in the northern hemisphere. And so in the traditional Jewish observance, the Passover feast begins with the Full Moon during the month of the Equinox.
What's in a Name?
The early church celebrated Passover in a similar manner to Jewish observances, though the customs changed over time. But our Christian Easter observance is still based on the Hebrew Passover observance. For example, many churches observe the solemn, penitent "Holy Week" observance before Easter, based on the seven-day Feast of Unleavened Bread.
Many people today argue that "Easter" is really a pagan holiday, with bunnies and eggs symbolizing heathen fertility rites, not the resurrection of Jesus. Entire books have been written to show that the name "Easter" is derived from the name of the Babylonian fertility goddess "Ishtar" or "Astarte." Eggs and bunnies are clearly not of Biblical origin. But the name issue is mostly a matter of the semantics of the English language since other European languages paint a different picture.
The Hebrew word for "Passover" is "pesach." In Greek, the translated word is "pascha." Throughout church history, this name has been associated with the feast of Christ's resurrection. This name of this feast is translated in the following ways in the languages of the traditionally Christian nations of Europe:
Spanish = Pascua
Italian = Pasqua
French = Paque
Russian = Pascha
Swedish = Pask
Norwegian = Paske
Dutch = Pasen
However, in the English language, the feast of Christ's resurrection is commonly called "Easter." For example, in Acts 12:4 in the King James Bible, the word "Easter" is given as a translation of the word "pascha." If you read old-fashioned English writings, it's not uncommon to see the Easter feast called "The Pasch" (pronounced "pask") and Jesus often figuratively referred to as "the paschal lamb" and so forth. However, the word "Pasch" is out of style in our shallow generation of English speakers.
It appears that the word "Easter" is derived from the name of an old Anglo-Saxon fertility goddess associated with the east who had a springtime festival. The German word is "Ostern," and since the Anglo-Saxons were originally a Germanic tribe, it's pretty clear that the words are related. While old habits apparently die hard in the English and German languages, it's pretty clear that most traditionally Christian nations name the Pasch as the proper name of the feast of Christ's resurrection.
The Reckoning of the Pasch
In the early days of the church, Christians kept the Pasch in the same manner as the Jews, beginning on the 14th of Nisan. But as time went by, Christianity developed distinctive observances that differed from Jewish practices.
In the church at Rome, it became customary to celebrate the Pasch on the Sunday following 14 Nisan, in order to commemorate Jesus' rising on the first day of the week. This became a controversy in the late Second Century. Victor I, the bishop of Rome, argued that the churches of Asia Minor should follow the Roman practice, rather than celebrate the Passover on 14 Nisan in the Jewish manner.
Since the early centuries, the Christian churches used the official Julian civil calendar of Rome to calculate the date of the Pasch. Since it was not always easy to know the date of the Equinox, calendar tables were prepared years in advance. The Roman method of calculating is explained here by the English scholar, the Venerable Bede, who wrote a definitive work on the subject around 700 A.D.: "The beginning of this month ought to be observed according to this rule, so that the 14th Moon of Easter never precedes the vernal equinox, but correctly appears either on the equinox itself (that is March 21) or after it has passed."
In the early centuries, during persecution by the Roman Empire, Christianity was a loose collection of local churches each led by an independent bishop. Since there was no central authority, not every local church agreed with the Roman method. For centuries, the various churches squabbled about the correct time for celebrating the Pasch.
A concord was finally established at the Council of Nicaea in 325 A.D. The Council of Nicaea is best known for establishing and affirming the doctrine of the Trinity. Other proclamations were made, including the method of calculating the date of Easter. The synodical letter of the Nicene council reported, "We further proclaim to you the good news of the agreement concerning the holy Easter.... all our brethren in the east who formerly followed the custom of the Jews are henceforth to celebrate the said most sacred feast of Easter at the same time as the Romans...."
The council emphasized that Easter should never occur during the Passover, due to antagonisms toward the Jewish people and some apparent inconsistencies in the Jewish calendar.
In this way, the Council of Nicaea established a common celebration of the Pasch. In the centuries following Nicaea, the church became increasingly uniform in other doctrines and practices, and centralized in authority. Nevertheless, the issue of Easter had come up again and again throughout church history, and there remain differences to this day.
A Slight Problem
As established by Julius Caesar, the solar year was reckoned as 365 days with an extra day added during a "leap year" every four years. In this way, the natural period of the seasonal year was understood to be 365 1/4 days in length. As explained by the Venerable Bede, "The Sun's year is complete when it returns to the same place with respect to the fixed stars after 365 days and 6 hours, that is a quarter of a whole day."
By this reckoning, the time from one Vernal Equinox to the next should have been 365 days, 6 hours. However, it was not known to either Julius Caesar or the Venerable Bede that in fact the solar year was precisely 365 days, 5 hours, 48 minutes and 42 seconds. As a result, the time from one Vernal Equinox to the next was overestimated by 11 minutes and 18 seconds.
We might be tempted to say that this is a tiny amount, what difference can 11 minutes make over the span of a year? Very little difference, but over a century of time, it can add up. This minor annual discrepancy amounts up to about three extra days every 400 years. And over many centuries, the accumulated days became considerable.
In the time of Caesar, the Vernal Equinox occurred on March 24. By the time of the Council of Nicaea, the Equinox was arriving on March 21. Throughout the Medieval period, the Equinox was arriving earlier and earlier. Consequently, the date of Easter was arriving earlier and earlier. Given enough centuries, Easter would regress backward through the calendar and begin to approach Christmas!
By the 1500s the Julian calendar had slipped 10 days from the Council of Nicaea, and the Equinox was arriving on March 11. Calendar reform became a topic for discussion among church authorities, in part because the nature of the problem was poorly understood. The revolutionary work of Mikolaj Kopernik (a.k.a. "Copernicus") was inspired by the effort to reform the calendar.
In 1543 he wrote, "When the Lateran Council was considering the question of reforming the Ecclesiastical Calendar, no decision was reached, for the sole reason that the magnitude of the year and the months and the movements of Sun and Moon had not yet been measured with sufficient accuracy."
(Of course, Kopernik's solution included the novel idea of placing the Earth in orbit around the Sun, but that's another story.)
The final solution was adopted 40 years later, in 1582. Upon consulting with the learned astronomers of the time, Pope Gregory XIII issued a proclamation that restored the calendar: "So thus that the Vernal Equinox, which was fixed by the fathers of the Nicene Council at March 21, is replaced on this date, we prescribe and order that there is removed, from October of the year 1582, the ten days which go from the 5th through the 14th inclusively. The day which follows the 4th, when one traditionally celebrates St. Francis of Assisi, shall be the 15th."
In this way, the Equinox once again arrived on March 21, as it had in 325 A.D. To accommodate future drift in the calendar, Gregory made the following provision, "Then, lest the Equinox recede from March 21 in the future, we establish that a bissextile (a.k.a. "leap year") shall be inserted every four years (as with the present custom), except in centennial years.... Thus, the years 1700, 1800 and 1900 will not be bissextile, and then, as with the habit with which we are accustomed, the year 2000 will have a bissextile intercalation day, as the day February 29, and that the same order of intermittent intercalations in each 400 year period will be preserved in perpetuity."
And so Gregory established that three out of four centennial years would not be leap years, so as to drop three days from every 400 years, and thus maintain the predictable order of Easter and the seasons. Remarkably, Gregory looked ahead from the Middle Ages to our lifetimes to establish that the year 2000 would be the first centennial leap year in 400 years. Sadly, our generation is so ignorant of classical astronomy that February 29, 2000 came and went with little or no notice, in the media or otherwise.
Gradual Acceptance
The reformed Gregorian Calendar was immediately adopted in October, 1582 throughout the Roman Catholic nations of Europe. But the Protestant and Eastern Orthodox nations resisted this "popish innovation."
One early Protestant proponent of the new calendar was the astronomer Johannes Kepler. In 1597, he argued with his superiors that it was "small-minded to demonstrate Protestant independence of thought by protesting against a most useful reform introduced by the Catholic Church."
For a century and a half thereafter, the nations of Europe maintained an awkward system of keeping two dates for every notable event, one in the "Old Style" of the Julian Calendar, and another in the "New Style" of the Gregorian Calendar. For example, one might notice that George Washington's birthday is sometimes given as "February 11, 1732 O.S., February 22, 1732 N.S."
Over time, the Protestant nations gradually accepted the Gregorian Calendar. In 1752, England finally adopted the New Style, and its American colonies followed at the same time. Here's how it was reported in "Poor Richard's Almanack" by "Richard Saunders," a.k.a. Benjamin Franklin: "...the King and Parliament have thought fit to alter our Year, by taking 11 days out of September, 1752, and directing us to begin our Account for the future on the first of January.... wishing withal, according to ancient Custom, that this New Year (which is indeed a New Year, such an one as we never saw before, and shall never see again) may be a happy Year to all my kind Readers."
Nowadays, the Gregorian Calendar has become the civil calendar that regulates the affairs of the entire secular world, including nations far and wide that have no historical Christian roots.
The Eastern Orthodox Church still retains the Julian Calendar for regulating its church calendar. By the 21st century, the seasons have slipped 13 days from the time of Nicaea. So the Vernal Equinox is now arriving on March 8, O.S. The Eastern Church celebrates Christmas on December 25 as reckoned by the Julian Calendar, which is January 7 on the Gregorian Calendar.
One principle objection of the Eastern Orthodox Church is that the Gregorian Calendar did not reiterate the Nicene prohibition against celebrating Easter after the Jewish Passover. As a matter of fact, we can witness this now in the year 2003. This month, Passover is on April 17, and the Gregorian Easter is on April 20. However, the Orthodox Easter is one week later, on April 27, in accordance with the decree of Nicaea.
So ironically, 1700 years after the Council of Nicaea established a common celebration of Easter, there is still disagreement over this very issue.
Jay Ryan is a former Contributing Editor to Sky & Telescope magazine. Now he applies all his efforts to the glory of God, especially for the benefit of Christian homeschoolers and other Christian kids. You can drop Jay an email at moonfinder@mangobay.com
Photo Credit: © Unsplash/Prottoy Hassan
This article is part of our larger Holy Week and Easter resource library centered around the events leading up to the death and resurrection of Jesus Christ. We hope these articles help you understand the meaning and story behind important Christian holidays and dates and encourage you as you take time to reflect on all that God has done for us through his son Jesus Christ!
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