כַּדּוּר הָאָרֶץ (kadur ha-aretz) — the globe / the spherical Earth

Etymology

The Bible contains the word כַּדּוּר (ball, Isaiah 22:18) and of course אֶרֶץ (earth), but never the compound כַּדּוּר הָאָרֶץ. This is unsurprising: the ancient Israelites, like the Babylonians, believed the world was a flat disk surrounded by a ring of water under a solid dome called the raqia (firmament). The idea that the Earth is spherical originated in Greece, where it is attested by the 5th century BCE and attributed to Pythagoras (6th century BCE); it was standard knowledge among educated Romans.

The Talmudic sages were aware of the Greek model. The Jerusalem Talmud (Avodah Zarah 3:1) states that "the world is shaped like a ball," but immediately qualifies this with a description of Alexander the Great ascending until he saw the world "as a ball and the sea as a bowl" — suggesting that the rabbis continued to hold a modified flat-earth model with the other side of the disk submerged in water. Only in the Geonic period, when Babylonian rabbis absorbed the broader Arabic-Greek scientific synthesis, did Jewish scholars fully accept Earth's sphericity. Rabbi Saadia Gaon (10th century) writes plainly in his commentary on Sefer Yetzirah: "Even though the view accepted by us is that the heavens and the earth each are like a ball, and the earth is inside the heavens like a point…" Not everyone agreed: Rabbi Hananel bar Hushiel in the early 11th century warned readers of his Talmud commentary to disregard astronomical claims that contradicted the biblical model.

The compound כַּדּוּר הָאָרֶץ as a technical term for the spherical Earth first appears in Solomon ibn Gabirol's philosophical poem Keter Malkhut ("Crown of Kingship," c. 1050–1070 CE): "Who can recount Your might, in making the globe (כַּדּוּר הָאָרֶץ) divided in two — half land and half water?" It is a calque of the Arabic al-kura al-ardiyya. The major works of Jewish philosophy of the period — Bahya ibn Paquda's Duties of the Heart (1080), Judah Halevi's Kuzari (1139), Maimonides' Guide of the Perplexed (1190) — all assert Earth's sphericity, but they were written in Arabic.

The decisive expansion of Hebrew astronomical-geographical vocabulary came with Rabbi Abraham bar Hiyya (Savasorda), who emigrated from Catalonia to Provence in the early 12th century. He found that the Jews of Provence could not read Arabic and were scientifically ignorant, and so (as he explains in the introduction to his Yesodei ha-Tevunah) he set out to translate the Arabic scientific corpus into Hebrew at the request of the community's leaders. In doing so he coined or standardized many mathematical and astronomical terms still in use: קֹטֶר (diameter, from Arabic qutr) — "the diagonal of the circle is a line dividing it in two, called in Arabic qutr" (Hibbur ha-Meshiha); קֹטֶב (pole, from Arabic qutb) — "the heavens rest on two points, one at the northern end called in Arabic qutb north and one at the southern end" (Sefer ha-Ibbur). Not all of Bar Hiyya's coinages survived: the equator he called אוֹפַן הַמִּישׁוֹר ("wheel of the level"), but modern Hebrew uses קַו הַמַּשְׁוֶה, which traces to Baruch Linda's Reshit Limmudim (1788) and was then the standard in Haskalah writings.

Key Quotes

"מִי יְמַלֵּל גְּבוּרוֹתֶיךָ בַעֲשׂוֹתְךָ כַּדּוּר הָאָרֶץ נֶחֱלַק לִשׁנַיִם, חֶצְיוֹ יַבָּשָׁה וְחֶצְיוֹ מָיִם?" — Solomon ibn Gabirol, Keter Malkhut, c. 1050–1070 CE

"ואף על פי שהדעה המקובלת אצלנו היא שהרקיע והארץ כל אחד מהם כמו כדור, ושהארץ בתוך השמים כמו נקודה" — Rabbi Saadia Gaon, commentary on Sefer Yetzirah, 10th century

"ואף על פי שהחוזים בכוכבים שבזמן הזה מדברים דברים המכחישים [את המודל המקראי], לא משגיחינן להו" — Rabbi Hananel bar Hushiel, Talmud commentary (Pesahim 94a), early 11th century

Timeline

• 6th–5th c. BCE: Greek philosophers establish Earth's sphericity; Pythagoras credited
• 3rd c. BCE: Eratosthenes calculates Earth's circumference with remarkable accuracy
• c. 2nd–5th c. CE: Talmudic rabbis aware of spherical model but retain modified flat-earth cosmology
• 10th c.: Saadia Gaon fully accepts Earth's sphericity
• c. 1050–1070: Solomon ibn Gabirol uses כַּדּוּר הָאָרֶץ in Keter Malkhut — earliest attested use
• 1080: Bahya ibn Paquda, Duties of the Heart (in Arabic); asserts sphericity
• Early 12th c.: Abraham bar Hiyya coins קֹטֶר and קֹטֶב; uses כַּדּוּר הָאָרֶץ in his Hebrew works
• 1139: Judah Halevi, Kuzari (in Arabic); asserts sphericity
• 1190: Maimonides, Guide of the Perplexed (in Arabic); asserts sphericity
• 1788: Baruch Linda's Reshit Limmudim uses קַו הַמַּשְׁוֶה for equator

Related Words

• כַּדּוּר — ball; biblical (Isaiah 22:18)
• קֹטֶר — diameter; coined by Abraham bar Hiyya from Arabic qutr
• קֹטֶב — pole; coined by Abraham bar Hiyya from Arabic qutb
• קַו הַמַּשְׁוֶה — equator; from Haskalah usage, not Bar Hiyya's אוֹפַן הַמִּישׁוֹר
• רָקִיעַ — firmament; the biblical dome over the flat earth
• כַּדּוּר הָרֶגֶל — football/soccer ball; modern use of the same compound