Have you ever wondered why Easter is scheduled on a different date every year unlike, for example, Christmas? The calculation of the date of Easter is based on astronomy.
With this activity, your students will explore the cycles that dictate the dating of Easter. Comparisons are made between Easter and other religious holidays such as Rosh Hashanah and Ramadan. The students will also explore the different types of calendars used for these holidays, calendars based on the moon, sun, or both. The basis for the counting of years for the three faiths are also presented. For example, the BC/AD counting system is based upon the birth of Jesus. The Jewish calendar is based on the Genesis account of creation occurring approximately 6000 years ago, and the Islamic calendar is based upon the Hegira, an event in the life of the prophet Mohammed.
The students will be able to create a chart of the dates of Easter, Rosh Hashanah, and Ramadan for a twenty year span of time. The influences of the yearly cycle of earth's revolution, and the monthly cycle of the moon's revolution around the earth, create the patterns seen in the chart.
The lab includes a detailed introduction (see below) and questions to accompany the graphing activity. Your students will create their graphs using colored pencils and the lab packet. An Excel sheet with the lab data and a graph is provided, which can be used as a demonstration.
If you are interested in teaching some of the history behind our calendars, and the specifics of differing faiths, then this lab will be a practical exercise to share with your students.
The Zip file download contains the lab handout and a key. An MS Excel sheet of the data is also provided, which can serve as a teaching demo. Files are included in both MS Word and PDF formats.
Calendar Graphs Lab Introduction
Have you ever wondered why the date of Easter is different every year? It is interesting to examine how the followers of the three large monotheistic religions measure time.
Nature provides two significant natural cycles that have been used to measure time: The year, based on earth’s revolution around the sun, and the month, based on the moon’s phases as it orbits around the earth. The holidays of the three faiths adhere to one or both of these cycles. The calculation of the dates of major religious observances such as Easter, Rosh Hashanah, and Ramadan are based on astronomy.
In Christianity, the calculation of the date of Easter was an early dilemma. In the Biblical account, the resurrection of Jesus took place just after the Jewish Passover, so the dating of Easter mimics the rule for the Passover (Table 01). The date of Easter also establishes the dates of other celebrations such as Ash Wednesday and Good Friday. Generally, the date of Easter is the “first Sunday after the first full moon after the Spring* equinox” (the Passover is the first full moon after the equinox). This rule was determined in the first few centuries of the Christian faith at the Council of Nicea in 325 CE. In this manner, Easter becomes a springtime festival, and it became linked to pagan European celebrations. The name of Easter itself was likely derived from the name of the Germanic fertility goddess Eostre. Rabbits and eggs are other remnants of these ancient traditions. In some years, Easter can occur just after the March equinox. The earliest possible date for Easter is March 22, which last occurred in 1818, and will next occur in 2285. The latest possible date for Easter is April 25, which occurred in 1943 and will occur again in 2038.
The Christian religious calendar was the sun-based Julian calendar of the Roman empire. One year is the same as one revolution of the earth around the sun, about 365.25 days. This calendar was reformed in 1582 by Pope Gregory XIII of the Roman Catholic Church, and this Gregorian calendar is our modern calendar and is still in use. The older Julian calendar had drifted away from the true seasons, and the new calendar was much improved.
The reckoning of years in the Christian calendar is based on the birth of Jesus. Years before the birth of Jesus are labeled BC, “before Christ”. Years after the birth of Jesus are labeled AD, which refers to the Latin phase “anno domini” or, “in the year of our Lord”. In recent years, references to Jesus have been removed from this system in order to make it more appealing to followers of other faiths. In the new reckoning, BC is replaced by BCE, “before the common era”, and AD is replaced by CE, “common era.” Despite these changes, the counting of years is still the same. I am writing this lab in the year 2017 AD, or 2017 CE. Socrates was put to death in 399 BC, or 399 BCE.
In contrast to Easter, the date of Christmas is fixed to December 25, which represented the date of the winter* solstice in the older Julian calendar. Today, the solstice usually occurs on December 21 in the Gregorian calendar. The link between Christmas and the seasons is much more direct than Easter. The solstice was the basis of important celebrations in the Roman empire, and these later became associated with the Christian holiday. Christmas assimilated many of the earlier pagan traditions of the solstice such as mistletoe, trees, and revelry and gift giving.
The Jewish religious calendar is mainly based on the phases of the moon. It features 12-13 months in a year. One month is the time needed for the moon to perform one orbit around the earth. Every 2-3 years, an extra “intercalary” month (intercalation) is added to keep the Jewish festivals in line with the seasons. Just like Easter, which is linked to spring, Rosh Hashanah, the Jewish New Year, occurs close to the autumn* Equinox and is an autumn* celebration. The date of Rosh Hashanah dictates the dates of other Jewish holidays such as Yom Kippur.
Years in the Jewish calendar are counted from year 1, the creation of the universe by God (Yahweh) as described in the Bible. In this system, October 2, 2016 to September 20, 2017 is the year 5777, which represents the age of the universe in Jewish religious thought. The belief in an approximately 6000-year-old universe is still held by some Jews and Christians. A young universe is not supported by scientific evidence, which indicates that the universe is 13.8 billion years old and had an origin termed the Big Bang.
The Islamic religious calendar is also based on the moon’s phases, yet it does not employ intercalation. It considers 354 or 355 days to equal one year, so Islamic celebrations tend to drift backward through the Gregorian calendar years. For example, Ramadan, the month of fasting, begins earlier each year, eventually cycling through the twelve Gregorian calendar months. Mohammed, the founder of the Islamic religion, forbade adding extra years to the calendar claiming that it violated the wishes of God (Allah).
During Ramadan, observant Muslims fast from sunrise to sunset. In the northern hemisphere, the length of day changes dramatically with the seasons. For example, from 40-degrees north latitude, winter days provide only about 9 hours of daylight, whereas summer days last about 15 hours. As a result, Muslims living in the temperate latitudes experience dramatic differences in the length of fasting as Ramadan cycles through the calendar year and seasons. A summer Ramadan fast is quite a bit longer than a winter fast.
The Islamic religious calendar counts years from the Hijra, the migration of Muhammad and his followers from Mecca to Medina. In this system, October 3, 2016 to September 21, 2017 is year 1438 AH, or “Anno Hegirae” in Latin.
In the activity that follows, you will examine the dates associated with each major celebration of the three religious faiths discussed above. You will prepare a graph that compares the dates of Easter, Rosh Hashanah, and Ramadan in order to discern the lunar and seasonal cycles that each is celebration is based upon.