More on Birkat Hachama

A couple of additional points about Birkat HaChama.

Firstly, for those in Modi'in, there will be a public recitation of Birkat HaChama on Wednesday at the Heichal Tarbut ("Cultural Center") on Emek Dotan (near Homes Place). Official announcement is as follows:

עיריית מודיעין- מחלקת הרבנות ומחלקת תרבות ואירועים- תרבות תורנית, מזמינים את הציבור בכל קהילות העיר, לקיים את מצוות ברכת חמה, מצווה נדירה המקיימים פעם ב- 28 שנה.
ביום רביעי, יד' ניסן תשס"ט 8.4.09 ,בשעה 5:45 בבוקר ברחבת היכל התרבות העירוני מודיעין.
במעמד הרבנים הראשיים למודיעין-מכבים-רעות
.בתכנית:
* תפילת שחרית-ותיקין ,
* סיום מסכת לערב פסח ,
* ריקוד מצוה.
תפילת שחרית מרכזית לכל בתי הכנסת בעיר: 5:45 בבוקר

The City of Modi'in - Department of the Rabbanut and Department of Culture and Events - Torani Department
Invite the public from all communities in the city, to fulfil the mitzvah of Birkat HaChama, a rare mitzvah that occurs once in 28 years.
On Wednesday, 14 Nissan 5769, 8.4.09 at 5:45 in the morning in the courtyard of the City Cultural Center (Heichal Hatarbut) in Modi’in.
With the participation of the Chief Rabbis of Modi’in-Maccabim-Reut.
The Program will include:
* Tfillat Shacharit “vatikin”
* Siyum Missechet for Erev Pessach
* Dancing
A Central Shacharit service for all the synagogues ion the city will begin at 5:45

Another thought about the calculation of Birkat HaChama and how it corresponds to the Julian and Gregorian Calendars.

One of the important factors in calculating Birkat HaChama is the length of a solar year (the time that it takes the Earth to rotate around the Sun). Chazal have two different calculations used to measure the length of a solar year.

• Shmuel uses a simple calculation of exactly 365.25 days in a Solar Year. This is the calculation we use for Birkat HaChama (see Eruvin 56a).
  
• Rav Adda bar Ahava makes a more accurate calculation and determines that a Solar year is 365 days, 5 hours, 55 minutes, and 25.44 seconds (or 365.2468 days). This is the calculation that we use for our more familiar 19 year cycle.
  

What I found interesting was that the Julian Calendar which was used by the Christian world from 45 BCE through until at least 1582 (or much later in some countries) is based on a solar year of 365.25 days.
This is identical to the calculation of Shmuel, hence according to Julian Calendar, Birkat HaChama always falls out on March 26.

When the Catholic Church moved to the Gregorian Calendar starting in 1582, the new calendar had a more accurate calculation for the Solar Year (which is accounted for by skipping leap years 3 times every 400 years). According to the Gregorian Calendar, a solar year is 365 days, 5 hours, 49 minutes and 12 seconds (365.2425 days), about 6 minutes shorter than the calculation used by Rav Adda.

The Gregorian Year is pretty close to an accurate solar year (which is calculated at about 365.24219 days), however to me it is amazing that Rav Adda managed to get a prettty good estimate more than a thousand years before Pope Gregory XIII instituted his calendar.