Our calendar is known as the Gregorian calendar, named for Pope Gregory VIII who established it in 1582. The Gregorian is a solar calendar since it is based on the earth’s rotation around the sun. The four seasons we enjoy result from the position change of the earth during it’s solar orbit. The Biblical or Jewish calendar is a moon or lunar calendar based on the movement of the moon around the earth. There are scientific and Scriptural foundations to the Jewish (Hebrew) calendar. Although considered to be a lunar calendar, it is actually luni-solar calendar operating on the motions of the moon with corrections to keep it in-sync with the sun which, in turn, determines the seasons. The luni-solar calendar is ancient, yet not unique to the Jewish people. Many Mesopotamian cultures (e.g., Muslims, Babylonians, Sumerians, etc.) used some variation of it. The way the Hebrew luni-solar calendar works; however, is unique.
Astronomers define a day as ‘the time taken for the earth to complete one revolution on it’s axis which equals 24 hours.’ Sunset is the start of the day on the Hebrew calendar according to Genesis 1:5. Six times in Genesis Chapter 1, the Lord spoke of the day consisting of ‘the evening and the morning’ (Genesis 1:5, 8, 13, 19, 23, 31). The day starting at sunset indicates that in God’s economy, the day is starting in the dark but is always heading towards the light. The Western world day begins at midnight and ends at midnight…we start and end in the dark. This is quite fitting with how human nature is…always in the dark, needing the light. The order of the day is consistent (evening then morning) so Jewish holidays always begin at sundown when the new day begins. This does pose a challenge. Sundown continually changes due to the tilting of the earth’s axis.
A quick gear shift to the number 7 which is pivotal to both Gregorian and Hebrew calendars. There are 7 days in the week. The Hebrew word for week (shavua) is derived from the word seven (sheva). Shavuot is plural for weeks and is used in reference to one of the feasts or appointed times given by God, the Feast of Shavuot (aka, Pentecost) which requires counting 7 weeks after the Feast of Firstfruits. The days of the Hebrew week are numbered, with Yom Rishon (Yom means day) being Sunday or the first day. The chart below provides all seven days. The only day that is not preceded by Yom, is the 7th day, Saturday, which is called Shabbat.
Shabbat was sanctified or set aside from the others as a special day (Genesis 2:3). God rested on the 7th day. He wasn’t exhausted; just finished with His work of creation. God has not created since then; however, He did put into place laws of conservation and preservation, known today as the laws of thermodynamics. God has been working since creation in His plan for redemption, but He has not been creating.
In a luni-solar calendar, the months are lunar based. The first day of the lunar month, Rosh Chodesh (means ‘head of the month’), always occurs on the New Moon. The New Moon cannot be seen at all because that is when the moon is behind the sun. The 15th day of the lunar month is always the Full Moon. The months and modern names of the Hebrew calendar (along with its Gregorian equivalents) are in the table below, listed in Biblical order.
The moon-based orbital month (called a ‘synodic’ month) is the period of time from the New Moon to New Moon and comes to approximately 29.5 days. Since a half day causes problems, 6 months have 29 days and 6 months have 30 days. Calculating the year is where this gets interesting. A true lunar calendar is a measure of the moon’s rotation around the earth which takes 354 days (12 orbital months X 29.5 days is approximately 354 days). Many Christian commentaries round the Hebrew year to 360 days; however, calculations based on 360 will be incorrect.
Each year the lunar calendar drifts away from the solar calendar. The Solar year (the time for the earth to revolve around the sun) is 365.25 days. The difference between the Solar and Lunar years is approximately 11 days (365.25-354 = 11.25). Since it is difficult to operate on ¼ of a day, every 4 years on the solar (Gregorian) calendar, we have a leap year, where 1 day is added to February (February 29th). This helps to keep the seasons in sync with the calendar.
The seasons are always determined by the sun. The moon has nothing to do with the seasons. Since the Hebrew calendar loses 11 days each year as compared to the solar calendar, every 3 years the Hebrew calendar loses over a month (33 days) against the solar calendar. In 9 years, the Hebrew calendar loses over 3 months (99 days), or a whole season. To stay in sync, the Hebrew calendar must compensate for the lunar drift away from the solar calendar (meaning a drift of the seasons as well). If adjustments were not made, after a few years, the feast days (appointed days by God) would be observed/celebrated in the wrong season of the year.
Moses ben Maimon (also known as Maimonides or Rambam) was a Jewish philosopher, Rabbi, Torah scholar, physician and astronomer in the Middle Ages. Maimonides developed the formula to synchronize the Hebrew calendar with the solar calendar in the 12th century (1178 AD) by adding a month (Adar II). This is referred to as the “leap year” on the Hebrew calendar, differing from the Gregorian ‘leap year’ which adds only 1 day (Feb 29th). To calculate where the leap year will occur, Rambam divided the Hebrew year by 19 and if the remainder was 0, 3, 5, 7, 11, 14 or 17…the year was a leap year. So what just what exactly is the Hebrew year?
The modern Hebrew calendar is dated from the time of creation with Rosh HaShanah (the ‘head of the new year’) as the first day. The Latin phrase ‘Anno Mundi’ stands for the “year of the world” and is abbreviated as AM. I started this post on the 25th of Tamuz, 5783 AM (Gregorian equivalent: July 14th, 2023). At sunset on Rosh HaShanah, Friday September 15th, it will be Hebrew year 5784 AM. Remember that on the Gregorian calendar, AD is Anno Domini (“In the year of our Lord”) and BC is “Before Christ” in the English phrase.
Continuing with the importance of the number 7 in the Hebrew calendar, every 7 years there is a shmita year – a sabbath year where the Jewish people are required to rest the land from sowing and harvesting (Leviticus 25:3-4). Every 7th years of shmita years is a Jubilee year. Seven shmita years is 49 lunar years and there was to be a Jubilee in the 50th year (Leviticus 25:8). In the year of Jubilee, all the land that had been purchased was to be returned to the original tribe that it came from, all debts were to be cancelled, and anyone who had sold themselves as an indentured servant was to be freed unless the individual decided to be a permeant indentured servant. Sadly, ancient Israel never observed the shmita year to let the land rest which resulted in many problems for them.
Another interesting fact about the Jewish calendar is that the Jewish people keep two calendars: the sacred calendar and the civil calendar. The sacred calendar was established by God when He delivered them out of Egypt. God told them that the day of deliverance was to be the beginning of the sacred calendar and that Nisan would be the first month of the year. This month was originally called Aviv (or Abib) but later was changed to Nisan during the Babylonian captivity (one of the ramifications of not honoring the shmita). Each month on the lunar calendar may come in one or two Gregorian months (refer back to the chart that lists the months of the year) because of the 11.25 days difference between the two. The civil calendar is based on the Jewish agricultural season and begins with the month of Tishri (September or October for us) which is the beginning of their agricultural season.
You may be wondering why our understanding of this information is relevant. Knowledge of the calendars helps us to understand God’s plan of redemption and salvation for all humankind through the person and work of Jesus Christ. This redemptive plan has a definite beginning, process and conclusion that is revealed in His prophetic seasons or feasts. These feasts are frequently referred as Jewish Feasts; however, they are Appointed Feasts set by God (Feasts of the Lord) for the Jewish people to celebrate at a certain time in a certain sequence as detailed in the Book of Leviticus . Understanding the Jewish calendar lays the groundwork for our future study of these Feasts and how they fit in God’s prophetic timetable. I can’t wait to dig into these Feasts and other Jewish holidays with you. Lord willing, we will start this journey in the next post.
Until then…keep your eyes on the skies for the times and the seasons. Shalom, haverot (peace, friends).
Love this ! Thanks for breaking it all down
I can’t wait to go through the feast
😁