Birchas Hachama

when: April 8, on a Wednesday (it’s always this date & this day because the english calendar goes according to the sun)

there are dozens of s’forim out, even a small english one called “Once every 28 Years”

aussieboy-

A solar year is approximately 365.25 days, so every fourth year the fraction will add up to an extra day (which is why we have leap years). Therefore in the beginning of the fifth year the sun will be in the same location as it was in the beginning of the first year.

(Let’s assume that the beginning of the first year was exactly at sunrise, the beginning of the second year will be at midday, the beginning of the third year will be at sunset, the beginning of the fourth year will be at midnight and the beginning of the fifth year will be at sunrise…)

Since there are 7 days in a week and the LCM of 4 and 7 is 28, it will take 28 years until the sun is in the exact same place in the sky on the same day of the week at the beginning of the year.

After 2100 Birchas Hachama will no longer be on April 8th (it will still be on a Wednesday though (the first one being April 9th, 2121)) because 2100 is not a leap year as far as the Gregorian Calendar is concerned but is according to Halacha. (From 1800 to 1900 it was always on April 7th.)

It stays a constant date on the Julian calendar, because both make the same assumption that the year is 365.25 days long, its not exactly. The civil calendar assumes that the year is 365 97/400 days long, which is still not exactly right but close enough to only drift 1 day in about 3200 years.

ZachKessin-

That’s correct, on the Julian Calendar the date is constant (April 5th), but the vast majority of the world switched to the Gregorian Calendar in 1582.

Dr Pepper, I know that, I’m a bit of an astronomy geek, and with that comes a fair bit of calendar knowledge. The catholic countries switched in 1582, England (and the Americas) not till 1750 something. Russia not until like 1905.

ZachKessin-

Once the Julian Calendar was dropped the date for Birchas Hachama was no longer constant. (It is constant from 1900 – 2100 but will be on April 9th begining 2100 as April 8th 2121 will be a Tuesday.)

Does anyone know what time birchas hacham falls out on that wednesday?

according to myZmanim the time of Hanetz Hachama where I live is 6:27:40

I watched the birchas hachama presentation oorah put out on their shmorg disc and it really gave me a good understanding of what birchas hachama is and how the whole solar system works, in a very well done graphical presentation with excellent narration. It is worth to take the time to watch so you can get a full appreciation of this mitzvah.