Hebrew/Jewish Calendar
- Current definition of Hebrew calendar set by Sanhedrin president Hillel II approx. AD 359
- combined solar/lunar calendar
- approximated tropical year=365.2468 days, approximated synodic month=29.530588 days
- one day on error in relation to solar year every 216 years
- Ordinary/common year: 353, 354, 355 days (12 months)
- Leap/embolismic year: 383, 384, or 385 (13 months)
- Three lengths termed “deficient”, “regular”, and “complete” respectively
- Every month starts approximately on the day of a new moon and their lengths are:
Name |
Length in Deficient Year |
Length in Regular Year |
Length in Complete year |
Tishri |
30 |
30 |
30 |
Heshvan |
29 |
29 |
30 |
Kislev |
29 |
30 |
30 |
Tevet |
29 |
29 |
29 |
Shevat |
30 |
30 |
30 |
Adar I |
30 |
30 |
30 |
Adar II |
29 |
29 |
29 |
Nisan |
30 |
30 |
30 |
Iyar |
29 |
29 |
29 |
Sivan |
30 |
30 |
30 |
Tammuz |
29 |
29 |
29 |
Av |
30 |
30 |
30 |
Elul |
29 |
29 |
29 |
Total: |
353 or 383 |
354 or 384 |
355 or 385 |
- Month Adar I is only present in leap years, in non-leap years, Adar II is called Adar I
- complete year created by adding day to Heshvan, deficient year created by removing day from Kislev
- years counted since creation of the world, assumed to be autumn 3760 BC
- after less than a week belonging to AM (Anno Mundi=year of world) 1, AM 2 started
- Hebrew year AM 5777 will begin 3 October 2016
- Several different days to choose from, most important:
- 1 Tishri: Rosh HaShanah (celebrates creation of world)
- 1 Nisan: New Year for Kings (start of religious year)
- Starts at either sunset or when three medium-sized stars should be visible
- Sunset marks start of the 12 night hours, sunrise marks start of 12 day hours
- Night hours may be longer or shorter than day hours, depending on season
- New year starts on day of new moon that occurs about 354 days (or 384 days if the previous year was a leap year) after 1 Tishri of previous year
- If new moon occurs after noon on that day, delay the new year by one day. (Because in that case the new crescent moon will not be visible until the next day.)
- If this would cause the new year to start on a Sunday, Wednesday, or Friday, delay it by one day. (Because we want to avoid that Yom Kippur (10 Tishri) falls on a Friday or Sunday, and that Hoshanah Rabba (21 Tishri) falls on a Sabbath (Saturday)).
- If two consecutive years start 356 days apart (an illegal year length), delay the start of the first year by two days.
- If two consecutive years start 382 days apart (an illegal year length), delay the start of the second year by one day.