John Pazmino
 NYSkies Astronomy Inc
 2009 May 9 initial
 2009 August 22 current
    On Monday and Tuesday, April 6 and 7, 2009, several Jewish friends 
called my attention to a ritual that occurs only once each 28 years. 
The ceremony is Birkat Hachama (BEER-kaht hah-chah-MAH), Blessing the 
Sun. They asked if I knew about it and could explain the astronomy 
behind it. Because it comes around once per generation, many folk 
never heard of it before now. Other Jewish friends elaborated about 
the ritual and pointed out interesting tradition and astronomy in it. 
    In 2009 it occurred at sunrise on Wednesday 8 April. The previous 
instance was on 1981 April 8. I can not recall anything of the 1981 
round. The next instance is 2037 April 8. Thus, a given person can 
enjoy three, likely at most, Birkat Hachama events. 
    There was extra attention and awareness in 2009 because Birkat 
Hachama occurred on the eve of Passover, an annual holiday of major 
importance for Jews. Thus, in this specific year of 2009, Jews got a 
double treat of astronomy within the same calendar day. 
    Birkat Hachama has various spelling in the Latin alphabet, much 
like other Hebrew words, because there is no uniform scheme of 
translitterating the Hebrew sounds into Latin characters. A similar 
situation applies to other languages that do not employ the Latin 
alphabet like Chinese, Arabic, Russian. Descriptions of Birkat Hachama 
commonly cross-reference other spellings. 
    Birkat Hachama thanks the Sun for its benefit for humankind, as 
part of the works of Creation. The ceremony technicly is conducted 
when the Sun is at the place and time he occupied when he was formed 
during the Creation. This is when the vernal equinox occurs at sunset 
on a Tuesday. 
    The Sun is not visible then for having just set. The ceremony is 
held on the first occasion that the new-born Sun comes into view, the 
very next sunrise on Wednesday. 
    The coincidence of time and place comes at intervals of 28 years. 
In the other years, the Sun comes to the same place, the vernal 
equinox, but not the time, sunset on Tuesday, or to the same time but 
not place. 
    The ritual is a gathering of Jews at or shortly after sunrise on 
the special Wednesday to recite certain Psalms and other odes. They 
offer gratitude to the works of Creation, specially to the Sun. 
    Some Jews explain that it is not proper to praise the Sun at other 
times, like at every sunrise, because it looks like idolatry and 
object worship. The intent of Birkat Haxhama is to thank the creation 
of the Sun at special instances. 
    Practice, at least in New York, varies among congregations. In the 
usual scene, the group meets at a synagogue or temple and stands in the 
shine of the Sun. It does not necessarily gaze at him but lets his 
rays fall on it. 
    If the sky is cloudy, as it was in New York on April 8th near 
sunrise, the group stands in open air where a Sun in the clear would 
shine on it. In a couple cases on Manhattan, due to high skyline, the 
group went to a nearby street corner for a sight line to the Sun. 
     Only under extremely adverse weather, a storm, may be ceremony be 
performed indoors. Some groups require in this case that they look out 
a window facing the Sun. 
    Some groups require that the ceremony complete within a stated 
period after sunrise. Others allow the ritual to procede at its own 
pace. SInce the odes are short and can be recited quickly, there seems 
to be problem to complete the celebration within a reasonable time. 
    The odes my be recited in either Hebrew or the native language. 
for New York, Hebrew is a common tongue among Jews, but it is good 
enough to sound out the Hebrew words from an phonetic script in the 
native language. 
    The groups disbanded after the ritual, not to convene again until 
the next round. The elder Jews welcomed the younger ones into the 
ritual and reminded these young ones to carry the tradition forward. 
It is possible that the current elders will no longer be around on the 
next celebration, 28 years later in 2037.  
    Birkat Hachama comes from the traditional story of Creation. For 
most Jews it is merely a cultural event, without implying the reality 
of the Creation story. Some Jews, however, sincerely believe that the 
Biblical story is a genuine history. 
    In the beginning there was Nothing. Then, at sunset on day #1 
there sprang forth Light. This moment is the first hour of the first 
day of the first month of the first year in the Jewish calendar. In 
modern notation, this was sunset (the first hour of the Jewish day) on 
Sunday 1 Nisan, year 1. Like just about all ancient cultures, the 
counting starts at '1', not '0'. 
    Jews still maintain this calendar, along side the civil calendar, 
so that the year count by 2009 is up to 5769. That is, the cosmos was 
born 5,768 years ago. We were in the 5,769th year of the world when 
this year's Birkat Hachama took place. 
    In modern chronology, the Creation began on -3760 April 13 on the  
Julian calendar. For dates before Caesar back into the indefinite past 
the Julian calendar is applied. This method gives a consistent, if 
artificial, dating to historical events that can be manipulated by 
calendar maths regardless of the era. 
    The cosmos developed day by day until day #4. At the sunset that 
initiated day #4 the Sun, Moon, stars, and planets were born. The Sun 
at this moment was placed at the vernal equinox point. He stood over 
the Earth's equator passing from south to north. This moment is the 
beginning of day #4, in hour #1, and also the beginning of the spring 
season on Earth.
    I here use the modern names for the weekdays. Many Jews go by day 
number. The week starts with Sunday, the first day of the world and 
ends on Saturday, the Sabbath, when all the Creation was finished.  
Day #4 is Wednesday. 
    Birkat Hachama takes place when the Sun is again at BOTH the 
vernal equinox AND the start of day #4. This aspect simulates the 
conditions during the week of Creation. That is, the Sun must be at 
the vernal equinox point and also set on Tuesday, which is when Jewish 
day #4 starts. 
    Since the Sun wasn't born yet for days 1 thru 3, the clock hours 
and day counts for events in these days are proleptic. Until the Sun 
and stars came along, the world was black with no way to count days 
or hours in any conventional manner. Jewish scholars speak of a 
virtual clock, somewhat the way cosmologists today work with a cosmic 
time keeping scheme. 
    Creation continued for several more days, culminating in the 
placement of humans on Earth in the sixth day. The seventh day, the 
Sabbath, was when the world had its first rest from the tasks and 
chores of being created. There after, the rest is history.
    The concept of a day of rest was almost a unique feature among 
jews. Just about all other peoples worked every day without setting a 
definite time for rest. Such a practice of suspending work on the 
Sabbath, every seventh day, was often deemed an act of laziness or 
slothfulness by outsiders. 
Vernal equinox 
    When the Sun and other celestial bodies were born, they were in 
animation in their paths thru the stars. At the moment of his  
creation the Sun was over the equator of Earth on his way from the 
southern hemisphere to the northern. This moment and place in the 
stars is the vernal equinox and is for the northern peoples the first 
day of the spring season. 
    The Sun's path is essentially a fixed great circle across the 
heavens, inclined 23-1/2 degree to the Earth equator. In terms of the 
day, the fundamental unit of time from antiquity all the way to the 
mid 20th century, the Sun takes about 365-1/4 days to do one lap of 
the heavens and return to the vernal equinox point. This is the year.
    For peoples in the mid northern latitudes, the cycle of the Sun 
from vernal equinox and return matched the cycle of the seasons, the 
flow and ebb of the bioculture that sustained them. Spring, occurring 
near the vernal equinox, started a new round of life and growth after 
the cold and inertia of winter. This correlation of solar motion and 
seasonal cycle caused most early cultures to start a new year at or 
near the vernal equinox. 
    The early Jews and the Babylonians from whom they borrowed much of 
their astronomy, knew quite well that the year is actually a trifle 
less than 365-1/4 day. he Jews settled on the rounded number for 
simplicity of calculation. By and by, they linked their chronology to 
the Julian calendar. On this calendar the vernal equinox occurred on 
March 25. 
    This is a few days later than the current date of March 20, due to 
accumulated discrepancies between the Julian and Jewish year of 365-
1/4 day and the true year length. Altho the small discrepancy builds 
up over the ages, sliding the vernal equinox to March 18 Julian, the 
Jews keep the March 25 historical date to calculate Birkat Hachama. 
    Jewish scholars explain that Birkat Hachama is a cultural, not an 
astronomy, celebration. In addition, there is nothing special about 
the arrangement of the other planets, stars, Moon. The Moon, the body 
that governs the Jewish calendar, is disregarded for Birkat Hachama. 
    The vernal equinox occurs at an instant that varies year to year. 
For Jewish calendar purposes the vernal equinox is set at only one of 
four hours. These are 00:00 (in civil time), 06:00, 12:00, and 18:00. 
These steps correspond to the 1/4 day extra each year over the 365 
full days. 
    These hours correspond about to midnight, sunrise, noon, and 
sunset. Because the Jewish day begins at sunset, these hours are the 
6th, 12th, 18th and 0th hour of a Jewish day. Except for critical 
situations, in the mid northern latitudes sunset is schematized to 
occur at 18:00 all year round. 
    Thus, the equinox may be at 06:00 in the first year, but must then 
occur at 12:00 in the next, 18:00 in the third, and 00:00 in the 
fourth. But by then the 1/4 days build to a full day, calling for the 
leapday in the Julian calendar. In this way the equinox is preserved 
with the same calendar day and the seasons stay lined up with the 
other months of the year. 
    In spite of the tiny but continual accumulation of discrepancy of 
the rounded and true length of the year, the Jews keep March 25, 
Julian, as the date of the vernal equinox. Jewish scholars know that 
this does not agree with the astronomy date of the equinox, nearer to 
Julian April 4 in the 21st century. 
Julian Calendar 
    The Julian calendar is arranged into twelve months of 30 or 31 
days, as developed by Julius Caesarand amended by Augustus Caesar. The 
year then began with March and ran thru february. This history is 
reflected in the 'number' months like October. October is no longer 
the 8th month, its original standing in the year. 
    The Julian year has 365-1/4 days. The 30/31 day arrangement of the 
months left a fractional month at the end. This, February, had only 28 
days. To honor his work, Julius renamed the fifth month after himself, 
our July. 
    Julius accounted for the extra quarter day by adding a full day 
every four years, He tacked this leapday to the end of the year, 
making 29 days for February. When the custom deve[oped of starting the 
year in January, the leapday stayed with February, now an interior 
month of the year. 
    Augustus Caesar amended the calendar to remove some mistakes in 
counting and took the sixth month to honor him, August. This is how 
the months are arranged thru today. 
    Since Augustus's time, the early years of the first century, the 
revamped Julian calendar remained on track. Some cultures still use it 
today parallel to the civil calendar.
    The mechancial addition of leapdays every fourth year, in the 
years evenly divisibe by 4, inserted too many extra days. The vernal 
equinox slided back in date by one day every 128 yers. The vernal 
equinox, on March 23 in Augustus's time, by now is on March 8 Julian. 
    The rule-of-four for Julian leap year is an absolute quirk of 
history. Augustus and later emprorers use various counts of years, none
related to the way leap year was announced. When the present AD scheme 
of year count was adopted, it was discovered that leap year was in the
years whose number was divided evenly by four. It sure didn't have to
happen this way!
    For years BC the algebraic count is empluted: 0, -1, -2, ^c. This
simplfies calendar calculations and also preserves the rule-of-four into
the infinite past. (Year 0 divided by 4 is 0 with no remainder.)
Jewish calendar
    The Jewish calendar is a lunisolar system of twelve months based 
on the cycle of lunar phases and adjusted periodicly to realign with 
the solar year. However, no actual year has 365 or 366 days. The year 
averages out to this length over a cycle of 19 years by the addition 
of leap months and jiggering the days within certain months. 
    Before the 4th century the Jewish calendar was managed locally by 
each community, resulting in erratic dating of events. Conversions to 
and from Jewush dates are now done with the modern scheme. For earlier 
epochs, this system is prolonged back in time, like the retrolongation 
of the Julian calendar to eras before Julius Caesar. 
    In primitive times the month began when a dedicated skywatcher 
declared that he saw the firstn cescent after New Moon. This is First
Moon and is still the official way some peoples today initiate a new 
month. It didn't take long to systematize the month start to a standard
rule without relying on weather and eyesight to catch the first glimpse
of the nww cycle of phases. The modern Jewish calendar has months of 
fixed or regulated number of days. 
    The Jewish year starts with the month of Nisan near the vernal 
equinox. In the Creation the cosmos came into being on 1 Nisan at 18h 
civil time of Saturday 13 April -3760. This was also the zeroth hour 
of Sunday. 
    The twelve lunar months total 354 days, 11-1/4 days short of the 
solar year. After a few years an extra, leap, month Adar II is added 
at the end of the year. With Adar II the Jewish year has 384 days.  
There are some other adjustments from year to year such that the 
length varies a day or two from these values. 
    The insersion of Adar II and other adjustments are strictly 
regulated such that the sequence of changes repeats every 19 years. In 
this span, there are 6939-3/4 days and 235 lunar phase cycles of 29.53 
days. The latter is built from appropriate mix of 29 and 30 day 
    This is why on the civil calendar the Jewish holidays seem to 
slide around year to year. Within the Jewish calendar the holidays are 
spaced at stated intervals downrange from 1 Nisan. In the last month 
or two of the Jewish year the dates get irregular but there are no 
significant holidays then. 
    The Jews celebrate two New Years. One is on 1 Nisan. The other, 
more common in modern times, is on 1 Tishri, the xeventh month. It is 
also the practice to index the year at this second New Year, on Rosh 
Hashanah. In this sense, Tishri can be the first month and Nisan, in 
the middle of the year, is the 7th (8th with Adat II) month, The year 
ends with Elul just before the next Tishri. It is at i Tishri, not 1 
Nisan, that the year count changes. A date in Elul is in one year and 
one in Tishri is in the next year. 
Day count 
    The Jews count days from sunset, not midnight. The date and day 
changes then so the afternoon is in one and the twilight and night are 
in the next. This is why the Jews start celebrating a holiday on the 
evening before the civil date. In 2009, as example, Passover begins on 
Thursday 9 April. The actual start of 'April 9' in the Jewish 
reckoning was at sunset of April 8th. That's when the first events of 
Passover took place. 
    Practice varies to count from the actual sunset, according to the 
season, or to schematize the sunset at 18:00 (civil time) all year 
round. In places that block view of the Sun or got persistently cloudy 
skies the 18:00 schematic sunset seems the better option. It is also 
the option where Jews interact strongly with the civil society. 
    In spite of counting days from sunset to sunset, I'm not aware of 
a Jewish clock ticking on this system. The clock hour in all Jewish 
writings I ever saw follows the civil clock. A certain meeting is 
booked for '21:30 on April 8th'. This means NOT 21:30 after sunset 
(which is when the instant day began), but 21:30 from the preceding 
midnight, or about 03:30 after sunset. 
    On the other hand, I do see that the number of the day sometimes 
is changed at sunset, so the hours before then are in one day number, 
like April 7th, and those after are in the next day number, April 8th. 
Absolutely ridiculous mixups can happen if the method is not carefully 
stated. It's like the confusion of when '12 AM' or '12 PM' occur. 
    When the Sun was born on the 4th day of Creation, so were the 
planets, Moon, and other objects in the heavens. To honor the 
formation of the planets, the first hour of the fourth day was given 
to the Moon, the first planet visible in twilight, before the sky 
darkened enough to reveal the others. This means a virtual sighting of 
the Moon, there not yet being humans on Earth to physicly witness her. 
    The second hour (19h civil) was given to the highest, farthest, 
planet to take care of. This was Saturn. The third hour (20h civil) 
was Jupiter's watch. Then Mars, Sun, Venus, Mercury, and Moon. The 
rank of planets inward toward earth was based on the apparent angular 
speeds thru the stars. Saturn moved the slowest; Moon, fastest. 
    After the Moon, the round of planets repeated. like the at-bat 
lineup of a baseball game. After three complete rounds of planets, 
there were three more hours left to start the fourth round. The The 
last hour, 23h civil, was looked over by Venus, and the very next 
hour, the zeroth hour of the next civil day, went to Mercuty. 
    After seven days of 24 hours each, the zeroth hour of the next day 
was again assigned to Saturn and the whole cycle began again for the 
next seven days. This is how the 7-day week was created. 
    The name of the weekday is that of the planet watching over its 
first, zeroth, civil hour. At the midnight of the civil day on which 
the Sun was born, Mercury took over the zeroth hour. That day was 
Mercury's day, Mercurii Dies in Latin, our Wednesday. 
    Jupiter handled the zeroth hour of the next day, Jovis Dies, 
Thursday. The last day of the week was ushered in by Saturn's care of 
its zeroth hour. This was Saturday, Saturni Dies, the Sabbath or Day 
oF Rest. 
    This scheme is tabulated here. The planets are given their Latin 
     hr | Sat | Sun | Mon | Tue | Wed | Thu | Fri | Sat | Jewish 
     00 | Sat | Sol | Lun | Mar | Mer | Jup | Ven | Sat | 06    | 
     01 | Jup | Ven | Sat | Sol | Lun | Mar | Mer | Jup | 07    | 
     02 | Mar | Mer | Jup | Ven | Sat | Sun | Lun | Mar | 08    | 
     03 | Sol | Lun | Mar | Mer | Jup | Ven | Sat | Sol | 09    | 
     04 | Ven | Sat | Sol | Lun | Mar | Mer | Jup | Ven | 10    | 
     05 | Mer | Jup | Ven | Sat | Sun | Lun | Mar | Mer | 11    | 
     06 | Lun | Mar | Mer | Jup | Ven | Sat | Sol | Lun | 12   THIS 
     07 | Sat | Sol | Lun | Mar | Mer | Jup | Ven | Sat | 13   day 
     08 | Jup | Ven | Sat | Sol | Lun | Mar | Mer | Jup | 14    | 
     09 | Mar | Mer | Jup | Ven | Sat | Sun | Lun | Mar | 15    | 
     10 | Sol | Lun | Mar | Mer | Jup | Ven | Sat | Sol | 16    | 
     11 | Ven | Sat | Sol | Lun | Mar | Mer | Jup | Ven | 17    | 
     12 | Mer | Jup | Ven | Sat | Sun | Lun | Mar | Mer | 18    | 
     13 | Lun | Mar | Mer | Jup | Ven | Sat | Sol | Lun | 19    | 
     14 | Sat | Sol | Lun | Mar | Mer | Jup | Ven | Sat | 20    | 
     15 | Jup | Ven | Sat | Sol | Lun | Mar | Mer | Jup | 21    | 
     16 | Mar | Mer | Jup | Ven | Sat | Sun | Lun | Mar | 22    | 
     17 | Sol | Lun | Mar | Mer | Jup | Ven | Sat | Sol | 23   \|/    
     18 | Ven | Sat | Sol | Lun | Mar | Mer | Jup | Ven | 00   /|\  
     19 | Mer | Jup | Ven | Sat | Sun | Lun | Mar | Mer | 01    | 
     20 | Lun | Mar | Mer | Jup | Ven | Sat | Sol | Lun | 02   NEXT 
     21 | Sat | Sol | Lun | Mar | Mer | Jup | Ven | Sat | 06   day 
     22 | Jup | Ven | Sat | Sol | Lun | Mar | Mer | Jup | 04    | 
     23 | Mar | Mer | Jup | Ven | Sat | Sun | Lun | Mar | 05    | 
    Over the ages various calendars were promulgated by various 
cultures. Months, day count, dates, year count were adjusted and 
altered. Such mutations of chronology is one of the massive problems 
historians and archaeologists face to map the history of peoples. 
    The circuit of weekdays remained stable since the beginning of the 
world. There never was any serious effort to add, remove, alter, 
shuffle the weekdays. They march on and on, planet after planet, day 
after day, across the ages. 
    By the sequence of the Creation, the Sun was born at sunset, the 
18th civil hour of Tuesday, the zeroth hour of Wednesday as the fourth 
day, and was placed in his vernal equinox position. On the Jewish 
calendar the Sun ws formed at the start of 4 Nisan, while the universe 
itself came about on 1 Nisan. This inaugurated year #1 in Jewish 
history, with this year of 2009 being the 5,769th since then. 
    Birkat Hachama is performed when these two factors next occur. I 
didn't discover the first documented celebration of Birkat Hachama, 
but it was likely conducted at least since the Roman era. I did find a 
news account of the first recorded (but not necessarily first observed 
or practiced) instance on Manhattan. On 1897 April 8 a group of Jews 
celebrating in Tompkins Square was disbanded by police for lacking an 
assembly permit. The police didn't understand the event, accepted that 
it was a peaceful one, yet noted that it still needed a permit. 
    Recall that the Jewish year has exactly 365-1/4 day and that the 
vernal equinox is schenatized to occur only at 00:00 (civil time), 
06:00, 12:00, 18:00. Each year, because of the extra quarter day, the 
vernal equinox notches six hours later on the calendar. When these 
amount to one full day, the Julian scheme adds a laepday, keeping the 
vernal equinox within the same calendar day. 
    If the vernal equinox fell at sunset on Tuesday in one year, when 
will it again do that? The table here gives the sequence of the two 
events from 1981 thru 2037, covering two Birkat Hachana intervals. 
     hour  | Tue  | Wed  | Thu  | Fri  | Sat  | Sun  | Mon 
     18:00 |*1981*|  --  |  --  |  --  |  --  |  --  |  -- 
     00:00 | 1986 | 1998 | 1982 | 1994 | 2006 | 1990 | 2002 
     06:00 | 2003 | 1987 | 1999 | 1983 | 1995 | 2007 | 1991 
     12:00 | 1992+| 2004+| 1988+| 2000+| 1984+| 1996*| 2008+ 
     18:00 |*2009*| 1993 | 2005 | 1989 | 2001 | 1985 | 1997 
     00:00 | 2014 | 2026 | 2010 | 2022 | 2034 | 2018 | 2030 
     06:00 | 2031 | 2015 | 2027 | 2011 | 2023 | 2035 | 2019 
     12:00 | 2020+| 2032+| 2016+| 2028+| 2012+| 2024+| 2036+ 
     18:00 |*2037*| 2021 | 2033 | 2017 | 2029 | 2013 | 2025 
    The leap years are marked with a '+'. Note carefully that year 
2000 was a leap year because it was an even multiple of 400. This is
a feature of the Gregorian calendar, that supplanted the Julian
calendar for just about all civil purposes.
    The vernal equinox occurs every year, but on different days and 
hours. It occurs at sunset (18:00 civil time) on Tuesday (civil day, 
start of Jewish day #4) only at intervals of 28 years. 
    For most Jews, there are three, possibly four, occurrences within 
a lifetime. A 1-year-old person in 1981 would be 57 years old for the 
2037 celebration and 85 for the one in 2065. 
    This year's Birkat Hachama is the 206th since Creation. There 
apparently was no Birkat Hachama on the very day the Sun was born 
because there was no human on Earth yet to celebrate it. 
    Passover is set for the first full Moon after the vernal equinox. 
The vernal equinox is still the schematic March 25 Julian, but the 
full Moon can occur any number of days there after from the very day 
of the equinox to almost a full lunation later. This latter happens if
there was a full Moon on the day before the equinox. 
    It is revoltingly tough to tell just when the Moon is exactly full 
with no optical assistance. The Moon looks pretty nice and round a day 
or two around the geometric Full Moon moment. Besides that, the full 
Moon could happen in an other timezone, out of sight of the local 
Jews. They see it either too early on the previous night or too late 
on the next night. 
    To get around these difficulties, the Jews put the full Moon to be 
on 15 Nisan, regardless of her actual aspect. Since 1 Nisan begins 
when at First Moon is sighted, usually one day after New Moon, this is
a reasonable work around. Full Moon does occur about 15 days after New 
Moon, or 14 after the first sighting. 
    For calculating Passover a floating vernal equinox is used, not a 
fixed one like the March 25th for Birkat Hachama. Passover by Jewish 
tradition must always come after the equinox, but with a short year of 
twelve lunar months, 15 Nisan could in some years fall before then.
    The addition of a thirteenth month, Adar II, from time to time by 
a strict schedule ensures that the vernal equinox occurs late in the 
instant year or early in the next, within one lunation. Then 1 Nisan 
can be safely observed as the First Moon after the equinox and 
Passover comes on the 15th of Nisan, well after the equinox.
    It is only chance that in this year of 2009 Passover comes on the 
same civil day, Wednesday 8 April, as Birkat Hachama. Coincidences are 
very irrgularly spaced, the last being in 1925. Some scholars noted 
that this was perhaps the closest interval between coincidences, the 
usual spacing is many, many centuries. The last instance before 1925
was in 1309 and then two in the 600s. 
    There is no special significance to the joint events in 2009, 
except for the better attention steered to Birkat Hachama by the 
adjacent Passover. 
    The table here gives the civil dates of equinox, First Moon (Nisan 
1) and Passover (Nisan 15) for 2000-2020. Remember that the Jewish day 
starts at 18h civil on the previous date. Passover on 2009 started on 
Apr 8. Note that the equinox is starting to slide on the Gregorian 
calendar from March 20 to March 19. This is a long tern trend with 
more frequent March 19 dates later in the 21st century. 
     year | equinx | Nis  1 | Nis 15 | Jewish equinox 
     2000 | Mar 20 | Apr  6 | Apr 20 | Apr 7 Fri 12h  leap year 
     2001 | Mar 20 | Mar 25 | Apr  8 | Apr 7 Sat 18h 
     2002 | Mar 20 | Mar 14 | Mar 28 | Apr 7 Mon 00h 
     2003 | Mar 20 | Apr  3 | Apr 17 | Apr 7 Tue 06h 
     2004 | Mar 20 | Mar 23 | Apr  6 | Apr 7 Wed 12h  leap year 
     2005 | Mar 20 | Apr 10 | Apr 24 | Apr 7 Thu 18h 
     2006 | Mar 20 | Mar 30 | Apr 13 | Apr 7 Sat 00h 
     2007 | Mar 20 | Mar 20 | Apr  3 | Apr 7 Sun 06h 
     2008 | Mar 20 | Apr  6 | Apr 20 | Apr 7 Mon 12h  leap year 
     2009 | Mar 20 | Mar 26 | Apr  9 | Apr 7 Tue 18h  BH event  
     2010 | Mar 20 | Mar 16 | Mar 30 | Apr 7 Thu 00h 
     2011 | Mar 20 | Apr  5 | Apr 15 | Apr 7 Fri 06h 
     2012 | Mar 20 | Mar 24 | Apr  7 | Apr 7 Sat 12h  leap year 
     2013 | Mar 20 | Mar 12 | Mar 26 | Apr 7 Sun 18h 
     2014 | Mar 20 | Apr  1 | apr 15 | Apr 7 Tue 00h 
     2015 | Mar 20 | Mar 21 | Apr  4 | Apr 7 Wed 06h 
     2016 | Mar 19 | Apr  9 | Apr 23 | Apr 7 Thu 12h  leap year 
     2017 | Mar 20 | Mar 28 | Apr 11 | Apr 7 Fri 18h 
     2018 | Mar 20 | Mar 17 | Mar 31 | Apr 7 Sun 00h 
     2019 | Mar 20 | Apr  6 | Apr 20 | Apr 7 Mon 06h   
     2020 | Mar 19 | Mar 26 | Apr  9 | Apr 7 Tue 12h  leap year 
    The April 7 date of the Jewish equinox comes from the declared 
March 25 Julian plus 13 days lag behind Gregorian. (25 March) + (13) = 
(38 March) = (7 April). This date is 18 days after the astronomy 
equinox of March 20. 
Gregorian calendar 
    In the Gregorian calendar the vernal equinox in 2009 fell on March 
20th. This is 18 days earlier than Birkat Hachama, occurring on April 
8th. The error is one of using a schematic calculation rather than one 
answering to the real motions of the Sun. Altho in early years, the 
equinox was on March 25 Julian (there being no Gregorian calendar 
yet). the Julian calendar used the 365-1/4 day length for the solar 
year. The fractional day excess over the true year length gradually 
shoved the equinox to March 11th by the 1500s. 
    The Gregorian calendar of 1582 modified the Julian system by first 
removing the extra ten days to get the equinox back to March 21. This 
is where it was when the rules for Easter were worked out in the mid 
300s. The day after 1582 October 4 is 1582 October 15. There are no 
valid dates between these limits. 
    The Gregorian calendar also fixed the leapdays by omitting them 
from century years that are not even multiples of 400. 1600 and 2000 
were leapyears, but 1700, 1800, 1900 were years of 365 days. Julian 
reckoning inserted leapdays in these years with the rule-of-four. 
These extra leapdays slided Julian three more days behind Gregorian 
since 1600 so that the total offset is now 13 days. 
    Most of the Catholic countries made the change immediately. Many 
others took decades and centuries to change over. In astronomy it is 
usually assumed that the conversion took place all over the world at 
once, which can lead to erroneous results if the astronomer's site was
still running the Julian system after 1582. 
    Based on the astronomy vernal equinox, Birkat Hachama is 
celebrated way too late in the year. The Sun on April 8 at sunrise is 
about 19 degrees east of the vernal equinox and about 7 degrees north 
of the equator. 
Rosh Hashanah 
    In other parts of Jewish culture the world was created in the 
autumn, not spring. Rosh Hashanah celebrates this event as one of the 
major Jewish holidays. It occurs on 1 Tishri, the 7th Jewish month 
or the first counting from this New Year. 
    Rosh Hashanah in 2009 is on 19 September. The year changes at Rosh 
Hashanah, not at 1 Nisan. In 2009 the year steps from 5769 to 5770. 
Like for all Jewish days, the observance starts on the previous 
evening at 18h civil. 
    Some Jews treat Rosh Hashanah as the date the universe was planned 
'on paper'. The creation in 'brick and mortar' came a half year later 
at the next 1 Nisan. 
    The use of alternative New Years is not all that strange. 
hydrologists work with a water year from April to the following March
in synch with the flow of rivers, at least in the mid north latitudes. 
Eclipse computations are based on a Bessel year, from when the Sun's 
longitude is 280 degrees to the next instance. This occurs near 
December 31. 
    Schools start their year on September 1 to gear up for the actual 
start of classes a week or so later. Governments keep records in a 
payroll year of exactly 52 weeks, i day shorter than a calendar year. 
Two extra weeks are added every five or so years to get back in step. 
    Businesses use a fiscal year that starts on April 1, July 1, or 
October 1. Club memberships commonly start on February 1 or March 1 to 
give time to process renewals that were due on January 1st. 
    There seems to be no great debate among rank-&-file Jews about 
this dual New Year situation. Jewish scholars do have discussions but 
on the whole the status quo is accepted and left alone. 
    It'll be a while, until 2037, before we have the next Birkat 
Hachama. That is comes only once in a generation and only three, or 
possibly four, times in a lifetime, makes it a special event to look 
forward to. It added an extra element to this year's Passover, adding
a positive enhancement to the Jewish experience. 
    The loose astronomy, like the fixed ediurnate date for the equinox 
throws the aspect of the Sun in the sky away from what it was during 
the Creation. On the other hand, Jewish scholars recognize this defect 
and treat Birkat Hachama as a cultural ritual, not an astronomy event. 
    No one I spoke with about Kirbat Hachama seemed to know of other 
astronomy-related or Creation-related celebrations with such a long 
interval between occurrences.