predates Hillel the Nasi. In the sixth century BCE,
during their captivity in Babylonia,
the Jews adopted the Babylonian names of months.
Before this, their months were numbered, not named.
The Babylonian calendar, like the Hebrew calendar,
was lunisolar.
Gradually, over hundreds of years,
teachers switched from direct observation
of agricultural events
to determine when to add an extra month to the year,
and, to determine the start of each month,
from direct observation of the first crescent moon
to adding synodic months
from the first year of the world,
Anno Mundi 1, thought to have occurred
on the sixth of September 3761 BCE
just before midnight, Jerusalem time.
In 1178, Maimonides codified rules
for calculating the points and periods.
Interesting aspects
It’s good that holidays and rituals
are kept in synch with the revolutions
of the earth, moon, and sun,
but there are many interesting
aspects to this calendar
such as counting years from Anno Mundi 1,
that is, from 3761 BCE in the Proleptic Gregorian calendar,
having each year start on Rosh Hashanah,
near the solstice, the time of year
when God created Adam and Eve,
counting a year by months and not by days,
having each day start at sunset
and so having no fixed length in minutes
having each month start with a new moon,
having a new moon start when its crescent is first visible,
calculating a synodic month to be 29 days,
12 hours, and 793 eighteenths of a minute,
having any extra month start before the last month,
so that the first month would be in the spring
having sunset occur when three medium-size stars are visible,
having different opinions as to when the date changes,
starting the day either at dawn or at sunrise,
having an hour be one-twelfth of the time
from sunrise to sunset, not a fixed number of minutes,
this being shorter in winter and longer in summer,
dividing the hour into 1080 parts
having a seven-day week,
not coincidentally the number of days
that God took to create the world,
and having Sunday be the first day of the week.
Having a calendar
is having good reasons
for all these decisions,
and then sticking to it.
Inaccuracies
To correct for the fact that twelve lunar months
fall short of the days needed for the earth to orbit the sun,
every two or three years the year gets an extra lunar month
(that is, for seven of every nineteen years comprising the Metonic cycle);
however, this year still falls short one day
(compared to the Gregorian calendar)
every 231 years, so what the heck?
One can get really serious about the synodic month
being about six-tenths of a second too long.
The actual length of the synodic month
varies by about thirteen and a half hours,
but it turns out that the tides
are making the month longer
while also slowing earth’s rotation,
so that no calendar is staying in synch.
That there are twelve signs of the zodiac,
twelve months of the year,
twelve sons of Jacob, and twelve tribes of Israel
should not be lost to the numerologists among us.
Zodiac
Babylonian
Hebrew
Aries
Nisanu
Nisan
Taurus
Ayaru
Iyar
Gemini
Simanu
Sivan
Cancer
Dumuzu
Tammuz
Leo
Abu
Av
Virgo
Ululu
Elul
Libra
Tashritu
Tishrei
Scorpio
Arakhsamna
Marcheshvan or Cheshvan
Sagittarius
Kislimu
Kislev
Capricorn
Tebetu
Tevet
Aquarius
Shabatu
Shevat
Pisces
Adaru
Adar
OK, well . . . we need a few years with thirteen months to
keep our months in synch with our years.
That there are twelve signs of the zodiac, twelve months of the year, twelve sons of Jacob, and twelve tribes of Israel should not be lost to the numerologists among us.
OK, well . . . we need a few years with thirteen months to keep our months in synch with our years.
See also in The book of science:
Readings in wikipedia:
Other readings: