Post: In this week's haftorah, we encounter the following pasuk:
הַיֹּשֵׁב עַל-חוּג הָאָרֶץ, וְיֹשְׁבֶיהָ כַּחֲגָבִים; הַנּוֹטֶה כַדֹּק שָׁמַיִם, וַיִּמְתָּחֵם כָּאֹהֶל לָשָׁבֶת
|22. It is He Who sits above the circle of the earth, and whose inhabitants are like grasshoppers, who stretches out the heaven like a curtain, and He spread them out like a tent to dwell.|
|the circle: Heb. חוּג, an expression similar to (infra 44:13) “And with a compass (וּבַמְּחוּגָה),” a circle (compas in O.F.).|
|and whose inhabitants: are to Him [lit. before Him] like grasshoppers.|
|like a curtain: Heb. כַדֹּק, a curtain, toile in French.|
What is the chug ha'aretz? Ibn Ezra explains that it means the curvature of the earth. Thus:
He points us to Yeshaya 44, just as did Rashi.
ישעיהו פרק מד
Then he says that this pasuk is ecidence that the earth is round and not square (/flat), despite there not being a requirement for the pasuk to prove this, for the matter is known with complete proofs.
This strikes me as somewhat out of the ordinary. While Chazal certainly take pains to make derashot or bring pesukim to show known things, such as the direction of Bavel or that the sun rises in the East, they had their own reasons for this. But I don't expect Ibn Ezra to be doing such.
Indeed, given that he mentions the competing theory (of רבועה), I would guess that he is trying to convince contemporaries. There are two methods of proof. There is scientific proof, and there is textual proof from Tanach. And different groups would respond differently to these different types of proof. (Rationalists vs. non-rationalists?) And so he brings the pasuk as evidence, while noting the extreme obviousness of this even without the pasuk.
(See the midrash cited by Rashi, and Mizrachi on that Rashi, for the view that the earth is not round but rather flat.)
While I am convinced by the scientific proofs, I am not convinced by the textual proof from this pasuk in Yeshaya. Radak on the pasuk writes:
היושב - כאלו אמר על השמים כי הם חוג הארץ כמו שיעשה אדם במחוגה העגולה, כי למחוגה יש שתי אצבעות האחת יעמוד ובשנית יקיף העגולה והנה הנקודה בתוך העגולה והארץ כמו הנקודה, כי היא התחתון שבעגולה והשמים סביב הארץ כמו העגולה.
ואמר: היושב –
דרך משל, כי אין לו מקום יתעלה מכל דמיון אלא כאדם היושב על מקום גבוה מאד ומביט במקום השפל ידמה לו הדבר הגדול קטן, לפיכך אמר ויושביה כחגבים, כמו שאמר: ונהי בעינינו כחגבים וכן היינו בעיניהם.
The circle of the earth refers to the heavens. And because of this distance, the inhabitants are like grasshoppers. And even according to flat-earthers such as Mizrachi, the rakia is curved, over the earth.
I don't know about the flat-earth / round-earth beliefs of Radak, but regardless, there is much to recommend this interpretation of the pasuk as it referring to the rakia, on its own merits provided by context.
Update: To counter claims that he was talking of a flat disk, besides what I wrote in the comment about this not being contemporary Muslim astronomy, see also this, from Ibn Ezra's Sefer haTeamim:
He discusses Ptolemy, who works with a spherical Earth, and refers to the earth as a galgal. He clearly knows the Earth is a sphere.