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The Jewish Concept of Time


If this were a regular year, then we’d be celebrating Purim in two weeks time!!!! However, this year is a Jewish leap year, so we still have 6 weeks until Purim. 

What’s a Jewish leap year all about? Well, unlike the Christian Calendar (Gregorian) which is a Solar Calendar, and the Muslim Calendar, which is a Lunar Calendar, our calendar is based on both the lunar and the solar cycles making it a “Lunisolar Calendar”. This being the case, we have to balance the difference between both cycles, to keep them in sync with our holidays, so that Pesach will always be in the spring and Sukkot in the fall. 

As you know, months are measured by one revolution of the moon around the earth. According to the Talmud, one complete revolution of the moon around the earth takes 29.53059 days. (This value is very close to the average value measured by NASA: 29.530588.) 

The common year in the Hebrew calendar includes 12 months. But there is a difference of about 11 days between 12 lunar cycles and one solar cycle. One complete rotation of the earth around the sun takes 365.25 days. Within a one-year period, 12 lunar cycles are completed in 12 × 29.53059 = 354.36708 days. Therefore, the difference between 12 lunar cycles and one solar cycle is precisely 365.25 − 354.36708 = 10.88292 days.

To synchronize the lunar counting of days with the solar cycle, leap years are added 7 times over a 19-year cycle (in years: 3, 6, 8, 11, 14, 17, and 19). This results in the month of Adar being doubled - Adar I and Adar II and having a 13-month Hebrew year.

A quick review of our Parsha highlights one major recurring theme throughout its legal code and that is the theme of time: 

  • Even after the Exodus, Jewish slavery exists, but it can only last for a few years.
  • If you hit someone and the court needs to determine the extent of the damages, we wait and see how long recovery takes.
  • There is a mitzvah to loan someone money, but you may never charge interest even if the loan is long term.
  • Collateral can be taken, but blankets and pillows must be returned daily. 
  • First born animals are given to the Kohanim, but they spend 7 days at home first. 
  • 6 years of work lead to shemittah 
  • 6 days of work lead to Shabbat 
  • There is a concept of Aliyah L’Regel (pilgrimage holidays). You would think you should visit G-d often, but Mishpatim says only three visits to the temple every year. Everything must happen like clockwork!

The parsha concludes that even the conquest of Eretz Yisrael will be contingent on time:

I will send a plague ahead of you, and it shall drive out before you the Chivi, the C’naani, and the Chiti. I will not drive them out before you in a single year, lest the land become desolate and the wild beasts multiply to your hurt. I will drive them out before you little by little, until you have increased and possess the land.

Takeaway: The parasha of Yitro, and particularly, the Aseret HaDibrot (10 Commandments), focus on eternal values and mitzvot that apply to our whole lives. Mishpatim introduces laws that come from time to time or are based on time. These time based mitzvot teach us to anticipate the mitzvot that come from time to time and appreciate the concept of time.