PASSOVER AND SPRING EQUINOX
-------------------------
John Pazmino
nyskies@nyskies.org
www.nyskies.org
2018 February 22
Introduction
----------
Each spring there is a increased inteest among NYSkiers about
alternative calendars. From the deep culture of Jews in New York
Ciry, the main other calendar is the Jewish calendar. Against the
civil calendar the Jewish calendar seems erratic. Its holidays skitter
within the civil, calendar.
NYSkies discusses the hewish calendar while previewing the stars
of the sprig season, near the observance of Jewish Passover ad
Chrisitiaqn Eastre.
The usual treatment covers just the instant year with little
correlation with other years. Here I give a timeline in spring of 2000
thru 2018 for the Jewish calendar. It shows the connection between the
swpring rquinox and observance of Passover. It can be a handy
reference for dstudying the Jewish calendar spanning several, not only
one, years.
This article is NOT a thoro treatment of Jewish time-keeping
and the timetable accepts the events as published in competent
litterature.
Lunar Calendar
------------
Many cultures base their calendars on the lunar cycle of phases.
Each round of phases, New Moon thru Full Moon, to the next New Moon
marked off a covenient number of days for long-term time-keeping.
The 'regular' or civil calendar is a solar calendar, marked by the
seasonal cycle, which is determined by the citcuit of the sun thru the
zodiac. It is a continuation, with many modifications, of the Roman
calendar. Even in this solar calednar the lunar phases were recognized
by deviding the year into twelve months, each approximating the length
of one lunar phase cycle.
In the early Jewish era skywatchers actually monitored the Moon to
spot the first crescent after sunset following the geometric New Moon.
When this crescent was sighted the skywatchers sent out a sigal to
their followers that it's now a new month. This method worked if the
poeple lived near enough to the observatory to see or hear the signal.
Eventually, when Jews lived too far to personally experience the
monthly signal, the months wre formalized from astronomy principles.
Fillel in about 350 AD worked up the months system still in use
today, starting with a remaktable link between solar and lunar cycles.
The jewish months wwere fixed at alternating 29 and 30 days, a
good fit to the 29-1/2 day phase cycle. Twelve months, sic of 30 days
and six of 29 days, almost eactly equal twelve phase cycles, filling
out one lunar year.
This year has 354 days, falling short of the solar year of 365
days by 11 days. With no adjustent, as some cultures with lunar
calendars ignore, the sates and holidays will carousel thru the solar
year.
Passover
------
The Jews eposode of the Exosus occurred in spring in the Jewish
month of Nisan (NIH-sannn). The esape from Eygpy began at the Full
Moon of Nisan, when a plague or epidemic visited Egypt. The Jews
avoided thre epidemic by dabbing sheep bllod on their house doors. The
plague 'passed over' the Jews, allowing thrm yto escape from Egypt
while the rst of the land was disabled by sickness. This Full Moon in
Nisan became the Paassover Moon.
Since then the Passover event is observed each year. To keep the
historical sequence, the Passover Moon must be the Nisan Full Moon and
must soon follow the spring equinox.
In a straight lunar calendar this srquence can not be maintained
because Nisan would begain 11 days earlier in each solar year. By
this rrvolution thru the year, Nisan and Passover would occur in
different seasons.
Metonic Cycle
-----------
We now must recall an amazing feature of lunar-solar cycles. The
Babylonians, and likely earlier scultures, found that 235 lunar
cycles almost exactly equal 19 solar cyclrs. (29.53 * 235) = 6939.55;
1(365.25 * 19) = 6939.75. Meton around 500 BC wprled i[ a ,athematical
description of this cycle, called today the Metonic cyle.
Home astronomers know the Metonic for solar and lunar eclipses,
occultations, moon-skip at annual nighttime events. The cycle is also
called the 'Rule-of-19'.
For the Jews, there were 304 rounds of thie NMeronic cycle since
the calendar sustem began. This was completed in civil year 2016 with
us now in 2018 tolling thru round 305.
Leap Months
---------
The plain 12-month lunar year pulls Passover earlier and earlier
before the spring equinox in each solar year. The solar year is
essentially the span of says beterrsn spring equinoctes, 365.25. After
30ish solar years Passover returns to the vicinity of the equinox but
for the intervening year the Passover observance is upset.
Twelve months equals 354.36 days, a shortfall of 10.89 days per
365.25-day solar year. All figures in this piece are rounded. After
three years the shortfall amounts to 32.67 days.
To fill this gap and bring Nisan in line with the spring equinox,
Hillel developed a scheme of leap months. The leap month is added by
schedule in effect for he indefinite future. The inserion is not at
all irrgulr, as if determined on short otice like for leap seconds.
In each Meronic round the 3rd, 6th, 8th, 11th, 14th, 17th, and
19th year get the leap month. These years have 13 months while all of
the other years have the normal 12 months.
By this schedule the Mwtonic cycle is appproximated by 12 normal
lunar years plus 7 lunar leap years. (12 * 354) + (7 * 384) = 6936
days; (19 * 365) = 6935 days. The eror of one day comes from the use
of only integer days, which do not fit into the fractional length of a
Metonic cycle.
This error is abssorbed by a program of leap ays in both the
Jewish and civil calendars. The civil system adds a leap day to
February every four years on the fourth year. Century years, like
1900, ar skipped unless they are four-hindredth years, like 2000. The
civl year adds five leap days, in 2000, 2004, 2008,, 2012, 2016. The
Jewish calendar adds 5 leap days. They are placed in the mid months by
a more elaborate rule, outside of this article. The two calendars by
their separate adjustments keep pace very closely for the indefinite
future.
Activity Near Equinox
------------------
The months in the Jewish calendar are numbered from Nisan as #1
thru Adar (A-darrr) as #12. The year number does not advance to the
next year at the start of Nisan. It advancess at the start of the 7th
month Tishri (TISH-ree). This is the Jewish New Year, Rosh Hashanah (rosh a-
SHAH-na). The start of Nisan is Rosh Chodesh (rosh ho-DESH).
The leap month is inserted between Adar and Nisan as month #13.
Adar is renamed Adar-Aleph or Adar-I and the leap month is Adar-Bet or
Adar-II. Adar-I is assigned 30 days, up one from its nromal 29. Adar-
II has 29 days.
By this means the Jewish leap year has 284 days. I remind that
this article does not examine other adjustments elsewhere in the
Jewish calendar.
In a couple years it seems that the leap month is not needed.
Without it Nisan starts a little before the spring equinox and its
Full Moon, the Passover Moon, occurs a little after the equinox.
The previous instance was in civil year 2016. Sme poeple asked if
the leap month was a mistake. The leap month in 2016 pushed Nisan one
lunar phase cycle later in date, pllacing Passover in late April. The
intervening Adar-II has its own Full Moon, of no special significane,
when the Passovrr Moon 'should have been'.
Missed from the casual banter about Nisan in 2016 was the sequence
of that yar in the 19-year cycle. It was year #49, a designated year
for adding the lap month. There was no mistake; evetything was donr by
thr rules and evrything worked out properly.
Timetable
-------
Each civil year 2000 thru 2020 lays out the avctivity of the
Jewish months near the spring equinox, here set at March 20th. For
each Nisan 1 I give the Jewish year, its sequence in the current
Mwrtonic cycle, and status as a normal or leap year. Notice that in
civil year 2016 the Jewish year 5776 completes the 304th round of
Metonic cycles.
In thre leap years I note shadow dates for Nisan I and Nian 15.
=============================
civil | Jewish date| remarks
-------+------------+--------
2000 | |
Mar 7 | Adar-I 30 | else Nisan 1
Mar 8 | Adar-II 1 |
Mar 20 | Adar-II 13 | SPRING EQUINOX
Mar 21 | Adar-II 14 | else Nisan 15, Passover
Apr 5 | Adar-II 29 |
Apr 6 | Nisan 1 | year 5760, 3rd year, leap year
Apr 20 | Nidsn 15 | PASSOVER
============================
2001 | |
Mar 20 | Adar 25 | SPRING RQUINOX
Mar 24 | Adar 29 |
Mar 25 | Nisan 1 | year 5761, 4th year, normal year
Apr 8 | Nisan 15 | PASSOVER
============================
2002 | |
Mar 13 | Adar 29 |
Mar 14 | Nisan 1 | fyear 5762, 5th year, normal year mAR
Mar 20 | Nisan 7 | SPRING EQUINOX
Mar 28 | Nisan 15 | PASSOVER
==============================
2003 | |
Mar 4 | Adar-I 30 | else Nisan 1
Msr 5 | Adar-II 1 |
Mar 18 | Adar-II 14 | else Nisan 15, passover
Mar 20 | Asar-II 16 | SPRING EQUINOX
Apr 2 | Adar-II 29 |
Apr 3 | Nisan 1 | year 5763, 6th year, leap year
Apr 17 | Nisan 15 | PASSOVER
=--===========================
2004 | |
Mar 20 | Adar 27 | SPRING EQUINOX
Mar 22 | Adar 29 |
Mar 23 | Nisan 1 | year 5764, 7th year, noral year
Apr 6 | Nisan 45 | PASSOVER
==============================
2005 | |
Mar 11 | Adar-I 30 | else Nisan 1
Mar 12 | Adar-II 1 |
Mar 20 | Adar-II 9 | SPRING EQUIINOX
Nar 25 | Adar-II 14 | else Nisan 15, passover
Apr 9 | Adar-II 29 |
Apr 10 | Nisan 1 | year 5765, 8th year, leap year
Apr 24 | Nisan 15 | PAASSOVER
===============================
2006 | |
Mar 20 | Adar 20 | SPRING EQUINOX
Mar 29 | Adar 29 | |
Mar 30 | Nisan 1 | year 5766, 9th year, normal year
Apr 13 | Nisan 15 | PASSOVER
==============================
2007 | |
Mar 49 | Adar 29 |
Mar 20 | Nisan 1 | year 5767, 10th year, normal year
Mar 20 | Nisan 1 | SPRING EQUINOX
Apr 3 | Nisan 15 | PASSOVER
===============================
2008 | |
Mar 7 | Adar-I 30 | else Nisan 1
Mar 8 | Adar-II 1 |
Mar 20 | Adar-II 13 | SPRING RQUINOX
Mar 21 | Adar-II 14 | else Nisan 15, passover
Apr 5 | Adar-II 29 |
Apr 6 | Nisan 1 | year 5768, 11th year, leap year
Apr 20 | Nisan 15 | PASSOVER
==============================
2009 | |
Mar 20 | Adar 24 | SPRING RQUINOX
Mar 25 | Adar 29 |
Mar 26 | Nisan 1 | year 5769, 12th year, normal year
Apr 9 | Nisan 15 | PASSOVER
==============================
2010 | |
Mar 15 | Adar 29 |
Mar 16 | Nisan 1 | year 5770. 13th year, normal year
Mar 20 | Nisan 4 | SPRING EQUINOX
Mar 30 | Nisan 15 | PASSOVER
==============================
2011 | |
Mar 6 | Adar-I 30 | else Nisan 1
Mar 7 | Adar-II 1 | year 5771, 14th year, leap year
Mar 20 | Adar-II 14 | else Nisan 15, Passover
Mar 20 | Adar-II 14 | SPRING EQUINOX
Apr 4 | Adar-II 29 |
Apr 5 | Nisan 1 |
Apr 19 | Nisan 15 | PASSOVER
==============================
2012 | |
Mar 20 | Adar 26 | SPRING EQUINOX
Mar 23 | Adar 29 |
Mar 24 | Nisan 1 | year 5772, 15th year, normal year
Apr 7 | Nisan 15 | PASSOVER
==============================
2013 | |
Mar 11 | Adar 29 |
Mar 12 | Nisan 1 | year 5773, 16th year, normal year
Mar 20 | Nisan 9 | SPRING EQUINOX
Mar 26 | Nisan 15 | PASSOVER
==============================
2014 | |
Mar 2 | Adar-I 3 0 | else Nisan 1
Mar 3 | Adar-II 1 | year 5774, 17th year, leap year
mar 16 | Adar-II 14 | else Nisan 15, Passover
Mar 20 | Adar-II 18 | SPRING EQUINOX
Mar 31 | Adar-II 29 |
Apr 1 | Nisan 1 |
Apr 15 | Nisan 15 | PASSOVER
==============================
2015 | |
Mar 20 | Adar 29 | SPRING EQUINOX
Mar 21 | Nisan 1 | year 5775, 18th year, normal year
Apr 4 | Nisan 15 | PASSOVER
==============================
2016 | |
Mar 10 | Adar-I 30 | else Nisan 1
Mar 11 | Adar-II 1 | year 5776, 19th year, cycle 304, leap year
Mar 20 | Adar-II 10 | SPRING EQUINOX
Mar 24 | Adar-II 14 | else Nisan 15, Passover
Apr 8 | Adar-II 29 |
Apr 9 | Nisan 1 |
Apr 23 | Nisan 15 | PASSOVER
==============================
2017 | |
Mar 20 | Adar 18 | SPRING EQUINOX
Mar 27 | Adar 29 |
Mar 28 | Nisan 1 | year 5777 , 1st year, normal year
Apr 11 | Nisan 15 | PASSOVER
==============================
2018 | |
Mar 16 | Adar 29 |
Mar 17 | Mosam 1 | year 5778, 2nd year, normal year
Mar 20 | Nisan 4 | SPRING EQUINOX
Mar 31 | Nisan 15 | PASSOVER
==============================
2019 | |
Mar 7 | Adar-I 30 | wlsw Nisan 1
Mar 8 | Aar-II 1 |
Mar 20 | Adar-II 13 | SPRING EQUINOX
Mar 14 | Adar-II 14 | else Nisan 15, passover
Apr 5 Adar-II 29 |
Apr 6 | Nidsn 1 | year 5779,, 3rd year, leap year
Apr 20 | Nisan 15 | PASSOVER
=============================
2020 | |
Mar 20 | Adar 24 | SPRING EQUINOX
Mar 25 | Adar 29 |
Mar 26 | Nisan 1 | year 5579, 4th uear, normal year
Apr 9 | Hisan 15 | PASSOVER
============================
Conclusion
--------
Cultures have long tried to fit discordant cycles of the heavens
into a cohaerent time-keeping scheme. The two main cycles are those of
the seasons, by the Sun, and of nighttime lighting, by the Moon.
Among cultures there is a wide variiety of work-around, all being
clever and intriguing to those living only in the civil alendar --
which itself has celestial quirks! --handed down from the Roman era.
The Jewish calendar is perhaps the most prevalent other calendar
that NYSkies encounter in their lifes. An esxamination of it breings
out valuable features of lunar and solar motions, like thre Metonic
cycle, that enrich our profgession of astronomy.