And, lastly, there is a certain region lying to the south of us which is said to be under the equator, where the poles fall on the horizon, and the sphere of the universe stands straight up, as it were (sphaera recta).
1987, Ernst Ettisch, The Hebrew Vowels and Consonants as Symbols of Ancient Astronomic Concepts, page 25
This sphaera recta, incidentally, is not just theoretically imaginable. An observer standing on the earthly equator can perceive this: when the sun is on the celestial equator during one of the two equinoxes, it rises, as everywhere, exactly in the East, vertically to the zenith, and in the evening it again declines vertically toward the West. At all other times it is positioned to the left or to the right of the equator and reaches its highest point to the north or to the south of the zenith.
2007, Shlomo Sela, in Abraham ben Meïr Ibn Ezra [aut.] and Shlomo Sela [ed., tr.], The Book of Reasons: A Parallel Hebrew–English Critical Edition of the Two Versions of the Text (BRILL, ISSN 0169815X, →ISBN, part four: “Notes to the Second Version of the Book of Reasons”, page 265
The term sphaera recta, lit. “right sphere,” refers to the phenomena that occur when the celestial equator is perpendicular to the local horizon. The celestial sphere is then said to be right, in the sense of upright or perpendicular, because the paths of the stars are perpendicular to the horizon.
