With Rosh Hashanah (Jewish New Year) around the corner, I thought it would be a good time to look at the Jewish calendar. You see, there’s really only one thing that I find bewildering about Judaism—the calendar. Growing up in the U.S. we’re steeped in the Gregorian calendar. It’s a stable thing for the most part. Every day the sunsets and a new day begins. Most of us are pretty much on the same page here. If I say fall starts on Monday, September 23 this year in 2019 we all know to which day I’m referring. The calendar seemed a simple thing until I after being introduced to the Jewish calendar.
First, let’s talk about the calendar we use here in the U.S. While I’m sure sometime in school I learned about the history of how we keep track of the days, in the back of my mind I thought we used the same calendar as the Roman’s did. We don’t, but it’s the basis of our modern adaption.
The Roman calendar has undergone many iterations and was originally based on the phases of the moon. Romulus, the first king of Rome, was allegedly the first person to revamp the Roman calendar. Under Romulus, there were 10 months, with 61 days unaccounted for in winter and the year began in March. The high priest determined the length of the months to keep the calendar in sync with the seasons, equinoxes, and solstices. Of course, politics got in the way of keeping this determination scientific because the length of the months determined how long an elected official stayed in office.
The next king, Numa Pompilius added two months: January and February to account for those extra days. September, which means the 7th month now became the 9th month. Julius Ceasar was the last major reformer of the calendar. He replaced the complicated lunar calendar with a solar calendar based on the sun’s revolutions. This led to some difficulties with leap years, which caused important holidays to no longer coincide with their associated astronomical events (like Easter with the spring equinox, a throwback to the pagan goddess Eostre—but’s that’s for a different post).
In 1582 the Gregorian calendar was introduced by Pope Gregory whose reformed the calendar to more accurately align our days and months with the Earth’s orbit around the sun. Really, this meant doing a better job of calculating when to add in a leap year. Some nations quickly adopted the new calendar while others took a little longer. For example, Greece didn’t adopt the Gregorian calendar until 1923.
The biggest controversy I remember surrounding the calendar is the designation for years before the birth of Christ—should we use BC (before Christ) and AD (after death or anno Domini, “In the year of the Lord”) or BCE (before the common era) and CE (common era). I was surprised to learn CE first appeared in 1708 and originated from the term, Vulgar Era.
In the early 1600s, Johannes Kepler (remember him, he proved we live in a sun-centered solar system) used Vulgaris aerae because he questioned the accuracy of Jesus’s birthday and therefore the use of AD. “Vulgaris” means common or a thing from the common people. Thus Vulgaris aerae translates to VE (Vulgar Era) meaning a common era. Jews started using VE in the 1800s to designate the western calendar since the Jewish one was by then quite different.
Simply put, the Jewish calendar is where the Gregorian started from long ago. It is based on the moon’s rotation around the Earth and the Earth’s rotation around the sun and it lopsided axis. When a thin crescent of the moon appeared this meant the start of a new month. Because this occurred every 28-31 days, the calendar was always in flux. The Great Sanhedrin, an assembly of 71 rabbis similar to a court (lesser Sanhedrin’s of 21 or 23 rabbis was appointed in each city), would determine how many days in the month depending on when the new moon was first visible. This made planning for holidays and bar mitzvahs difficult because the dates were always in flux.
In the fourth century under Hillel II, the Great Sanhedrin’s last official act was to adopt a perpetual mathematically fixed calendar. Under the new calendar, every month has a set number of days except for three. A big problem with fixing the calendar is there are 12.4 lunar months in a solar year. To solve this, the Jewish calendar operates under a 19-year cycle with 235 lunar months (6939, 6940, or 6941 days) in total.
| Month | Number | Length | Approx Gregorian Equivalent | Special Dates |
| Nissan | 1 | 30 days | March-April | Passover |
| Iyar | 2 | 29 days | April-May | Lag B’Omer |
| Sivan | 3 | 30 days | May-June | Shavuot |
| Tammuz | 4 | 29 days | June-July | |
| Av | 5 | 30 days | July-August | Tisha B’Av |
| Elul | 6 | 29 days | August-September | |
| Tishri | 7 | 30 days | September-October | High Holidays: Rosh Hashanah & Yom Kippur, Sukkot, Shmini Atzeret, and Simchat Torah |
| Cheshvan | 8 | 29 or 30 days | October-November | |
| Kislev | 9 | 30 or 29 days | November-December | Chanukah |
| Tevet | 10 | 29 days | December-January | |
| Shevat | 11 | 30 days | January-February | Tu B-Shvat |
| Adar (Adar I in leap years) | 12 (13 in leap years) | 29 days 30 days | February-March | Purim |
To realign the lunar and solar years, an extra month, Adar I, is added to the Jewish calendar every 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years in the 19-year cycle. This is akin to the Gregorian calendar’s leap year and is referred to as “Shanah Me’ubret” meaning “a pregnant year.” Also, the first month of the year (Nissan) is in spring, but the Jewish new year, Rosh Hashanah, is in the seventh month (Tishri).
Confused yet? One easy thing to remember is the Jewish days of the week. They’re referred to as the first day beginning with Sunday, second day, etc. Easy.
| Day of Week | Translation | Gregorian Equivalent |
| Yom Rishon | First Day | Sunday |
| Yom Sheini | Second Day | Monday |
| Yom Shlishi | Third Day | Tuesday |
| Yom R’vi’i | Fourth Day | Wednesday |
| Yom Chamishi | Fifth Day | Thursday |
| Yom Shishi | Six Day | Friday |
| Yom Shabbat | Sabbath Day | Saturday |
Finally, the numbering of the years. Currently, it is the year is 5779. This is the number of years since the beginning (many point out that while Creation took 7 days, these were not 24 hours days). Rosh Hashanah, the Jewish New Year, begins this year on Sunday, 29 Sept and ends after on Tuesday, 1 October. Welcome 5780. More on Rosh Hashanah next post.
I was born in January 1974. This means my Jewish date of birth is Shevat 5734 (look up your Jewish birth date). On the same day each year, generally the same portion of Torah is read. For my date of birth, this is Parshat Beshalach (Exodus 13:17-17:16). This reading covers the day Moses parted the Red Sea, brings forth water from a rock, and causes manna (food) to rain down. Not a bad day to be born.
