In Oorah's 2009 Shmorg video, one of the tracks is about Birchat Hachama, and at around the 10 minute mark, the narrator states the following (I'm paraphrasing):

The Sforno writes that before the flood, the Earth's equator was coplanar with the celestial equator. Due to the sins of mankind, Hashem tilted the Earth to its current position of 23.5 degrees from the celestial equator.

Where does the Sforno say this? What can we learn from his commentary?

Background information:

  1. In this context, the celestial equator is the plane extending from the equator of the sun.
  2. Birchat Hachama is a blessing recited once every 28 years upon seeing the sun in the spot it was created in.
  3. For those unfamiliar with Oorah, it is a kiruv organization. Every year, they hold a fundraiser that sometimes involves mailing out a Jewish-themed DVD called the Shmorg.
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    Consider asking "What else does rabbinic literature say about the tilt of the Earth?" as a separate question. – mevaqesh Mar 15 '17 at 3:28
  • @mevaqesh That was my main concern, but I suspect that rabbinic literature says comparatively little about the tilt of the Earth. – user13937 Mar 15 '17 at 23:46
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    The Malbim makes a similar point and mentions the precise tilt angle of the Earth. Stating that (post flood) the seasons came into being by the Earths tilt. This caused people/animals to be sick due to changing weather. He even says that archaeologists find "elephants frozen in ice" because of changing climate post flood......... – bondonk Mar 28 '17 at 18:53

The Seforno (c.1500) writes this in is commentary to Genesis (8:22):

עוד כל ימי הארץ זרע וקציר וקור וחום וקיץ וחורף ויום ולילה לא ישבותו. "לא ישבותו" מלהתמיד על אותו האופן בלתי טבעי שהגבלתי להם אחר המבול, וזה שילך השמש על גלגל נוטה מקו משוה היום, ובנטיתו תהיה סבת השתנות כל אלה הזמנים, כי קודם המבול היה מהלך השמש תמיד בקו משוה היום, ובזה היה אז תמיד עת האביב... כי אז ישיב מהלך השמש אל קו משוה היום כמאז

They [the seasons] will not cease to function consistently with the system I set after the deluge. The sun will orbit predictably, its orbit will be subject to calculation and its divergence will cause all of the seasons, for before the deluge the sun had remained at a fixed distance relative to the earth all year round, its orbit being circular, resulting in eternal spring ... [In the future] the sun will once more orbit like a circle instead of like an ellipsis.

This translator understands שילך השמש על גלגל נוטה מקו משוה היום as a circular orbit vs. an elliptical one. (The Seforno speaks of the sun's motion, not the earth's but that seems immaterial to the discussion at hand). Before the deluge the orbit was circular and only afterwards did the orbit become elliptical causing seasons.

However, it should be noted that in reality, the elliptical orbit and resultant variable distance to the sun has little to do with the seasons. In fact, Earth is closest to the Sun, around the Northern Hemisphere's winter solstice, while it is farthest away from the Sun, around the north's summer solstice.

However, the seasons are caused by the Earth's tilt. If this is what וזה שילך השמש על גלגל נוטה מקו משוה היום means, then the Seforno would be more correct. Were the earth not tilted, then indeed (IIUC) the Earth's equator would have been coplanar with the celestial equator.

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    Thank you very much. I really do not mean to be pushy, but a translation would be greatly appreciated. – user13937 Mar 15 '17 at 2:50
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    Very normal request. Not pushy at all. The link to Sefaria ought to take you to a translation. I am working on modifying the translation a little...16th century Hebrew astronomical terms are a little difficult... I am largely depending on the Sefaria translator... – mevaqesh Mar 15 '17 at 3:28
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    So in summary, the Sforno did not speak specifically about the tilt of the Earth, but rather that the seasons changed after the flood? (E.g. he says "תמיד עת האביב"). – user13937 Mar 15 '17 at 23:54
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    No. He he refers to שילך השמש על גלגל נוטה מקו משוה היום which I am uncertain how to translate. I suspect, however, that that refers to the path that the sun travels through the sky, which does indeed correspond to both the earth's tilt and to the seasons. @HaLailahHaZeh – mevaqesh Mar 15 '17 at 23:56
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    I would translate it as sent the sun on [its] wheel (i.e. apparent orbit), tilted from the path (i.e. orbital plane) [which causes] equalizing of the day[s], so I understand this as causing seasons by tilting Earth's axis from its orbital plane. – Adám Mar 28 '17 at 5:44

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