Here is the passage of Talmud Bavli:
תנו רבנן: הרואה חמה בתקופתה לבנה בגבורתה וכוכבים במסילותם ומזלות כסדרן, אומר ברוך עושה בראשית. ואימת הוי? - אמר אביי: כל עשרים ושמונה שנין, והדר מחזור ונפלה תקופת ניסן בשבתאי באורתא דתלת נגהי ארבע
Rav Bar-Hayim refers to the following Talmud Yerushalmi:
הרואה את החמה בתקופתה ואת הלבנה בתקופתה ואת הרקיע בטיהרו אומר ברוך עושה בראשית אמ' רבי חונה הדא דתימר בימות הגשמים בלבד לאחר שלשה ימים הה"ד ועתה לא ראו אור וגו' הרואה את הלבנה בחידושה אומר ברוך מחדש חדשים
The statement of Abaye in Talmud Bavli comes to explain a Beraita, which says, among other things, that the Beracha "Baruch Oseh Bereshit" should be said when the Sun is seen in its Tekufa. The Yerushalmi has basically the same Beraita, but does not explain anything similar to what Abaye says. Instead, after bringing the Beraita, the Yerushalmi brings the teaching that we should say a blessing when after three days of rain, the sky clears up and we can again see the Sun.
Rav Bar-Hayim brings Rav Saadia HaGaon's interpretation of the Beraita. Rav Saadia suggests that we should say Birkat HaChammah every year at the Summer Solstice. Rav Bar-Hayim interestingly contends: "The statement [of Abaye] is almost certainly based on a sectarian solar calendar, such as that mentioned in the Book of Jubilees. Thus the entire concept contradicts Hazal who worked with a lunar calendar."
I think the Rav says many truths, but misses one insight. It seems to be true that the statement of Abaye was added after the Gaonim. However, this does not make this statement a corruption. The final redaction of the Talmud only occurred at the time of the latest Gaonim. Also, it seems to be true that Birkat HaChammah is the remnant of something apparently (but not really) extraneous: Jewish Astrology.
My view is the following.
The Beraita records a Takana from the beginning of Bayit Sheni. After the Churban, it was written down as a Beraita, intended for those who understood Jewish Astrology. It relates to the Sun, the Moon, and to the planets and the Mazalot (in the Bavli; the Yerushalmi mentions the sky, Rakia, instead of the planets and the Mazalot). The masses never knew Jewish Astrology, and the Sages would not write about it. Therefore, the Talmud could initially not explain the Beraita. We see this in the Yerushalmi, which brings the Beraita, and then in fact does not explain it. The statement about saying a Beracha after three days of rain is not an explanation, but an independent teaching, which naturally connects to the mentions of the Sun and the sky in the Beraita. Talmud Yerushalmi connects the Beraita's mention of the Moon to the Mitzva of Kiddush HaChodesh, which is a primary Mitzva of the Torah and clearly not the subject of the Beraita - Baruch Oseh Bereshit is not the Beracha for Kiddush HaChodesh.
Therefore, neither Talmud Yerushalmi nor Talmud Bavli offer an explanation for the Beraita's reference to the Moon. No explanation is found in the Bavli regarding the planets being in their paths and the Mazalot being in their order. No explanation is found in the Yerushalmi regarding the sky being in its purity (unless Rav Josh Waxman is right). It seems to me that Rav Saadia Gaon agreed that the Yerushalmi does not explain the Sun-part of the Beraita, as it does not explain what is the Tekufa of the Sun. This is why he suggests his own interpretation for what this Tekufa would be.
For many centuries, the proper explanation of the Beraita was left a secret tradition about Hanhagat HaOlam, known only to a select group of Jews. The explanation regarding the Tekufa of the Sun was added to the general Talmud in a very late stage. It is not correct to conclude from this that the Takana itself was late, or Chas V'Shalom a corruption.
I would like to suggest to the Rav that the Takana of Birkat HaChammah is self-dating, because the year of Rav Shmuel is not accurate. As history progresses, Tekufat Nissan, and therefore Birkat HaChammah, shifts towards the Summer, one day for every 128 years. In our days we say Birkat HaChammah on April 8, approximately 18 days after the Spring equinox. Tekufat Nissan coincided with the Spring equinox in the very beginning of Bayit Sheni. The Takana was issued by prophets.
מט
