But did you remember to add the other prayer for rain last week? I apologize; I would have reminded you, but my computer's been in the shop for a week. But the magical Mac is back, and so am I!
This change to the Shemoneh Esrei is actually one of the ones I remember best because it seems so strange that we add it on the night of December 4th (5th in a secular leap year). It's a random date, long after we're already praying for that rain in Israel, and it's measured by the civil calendar instead of the Hebrew one. Weird city, right?
This prayer is linked to the autumn equinox, which we recognize with our English calendars but not the Hebrew one. December 4th is apparently 60 days after the autumnal equinox ("equal night," if that helps you remember!). But which autumnal equinox? There is tekufat Tishrei (halachic autumn) and the one on the secular calendar. The Hebrew date for autumn changes each year, but the secular calendar gives us a steady date every year. However, in the year 2100, we'll move a day forward, to December 5 (and 6th in leap years). You learn something new every day! Chabad has an article with the detailed date calculations historically and today, if that floats your boat.
Why the Date Separation?
Let's get historical! There was a break between praising Hashem for rain and asking for rain in order to let pilgrims travel home safely from the High Holydays in Jerusalem. Rain was pretty inconvenient for traveling in those days. Accordingly, in Israel, the prayer is added according to the Hebrew calendar, the 7th of Cheshvan (sources are in the Talmud tractate Taanit.). I didn't know that, and you can read more about why the diaspora developed a different date on the Chabad website.
It's important to remember that we still measure the rainy season based on Israeli agricultural needs. Despite discussions about adjusting the prayers to the location of the davener, the same schedule of rain prayers are recited even in the high summer of the Southern Hemisphere. If your community/country needs rain, there is a prayer that can be added to the service elsewhere, and you can always add your own request for rain (or anything else) during the personal petition part of the Amidah. (That's during the prayer Shema Koleinu, the prayer for the acceptance of prayer.)
Funnily enough, the Talmud discusses that the prayer for rain should actually be earlier that Shemini Atzeret: at the beginning of Sukkot. But why pray for rain right before you're going to spend a week sleeping and eating outside in your hut? We have an obligation to be in the sukkah, so why pray for something that would prevent us from fulfilling that obligation? Though perhaps we should be thankful if it rains since Israel needs all the rain it can get. (Avoiding a cold and inconvenient sukkah is just a bonus, of course - heresy!)
Why Two Prayers?
But the fact that we pray for rain twice continued to bug me, so I looked into it. Solely for your benefit, of course.
The first prayer for rain is actually a praise for rain: “He causes the wind to blow and the rain to fall.” It's in the second blessing, known as Gevurot (Strengths/Powers), which is about the powers of Gd; not least of which is raising the dead. Apparently Sephardim have a different and longer version of this bracha. Intellectually, I know that the first three brachot of the Amidah are restricted to praises of Gd, not supplications, but when you call something "the prayer for rain," your brain makes assumptions.
The second prayer for rain is in "the Blessing of the Years." This is the actual request for rain. That makes sense since it's a prayer for a bountiful harvest.
Removing the Prayers Each Spring
Thankfully, both prayers end at the same time: erev Pesach (the day before Passover).