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"There are two colures or tropics on the sphere that go by the names solstitial and equinoctial. They are called colures from the Greek word colon, and the word for wild oxen… They are called this because just as the tail of the wild oxen inscribes a semicircle when it begins to move, so the line of the colure is only half-visible and even though it is a great circle it appears to us as incomplete." (Cosmographiae introductio, chap. III - Hessler 2008)