The *Tusi couple* is a mathematical device in which a small circle rotates inside a larger circle twice the diameter of the smaller circle. With this relationship of diameters, each point on the circumference of the smaller circle actually follows a linear path as the rotation occurs. Here’s a link to a video so you can see it in motion.

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I learned something new by delving into the new textbook Professor Megan Raby selected for her UTeach Perspectives Class Spring Semester.

That week we would be focused on the Copernicanism and the Scientific Revolution, so anything with a math connection to astronomy would fit well. The new textbook I’m using, James Poskett’sHorizons: The Global Origins of Modern Science, integrates a lot about how Arabic astronomical observation influenced the Sci Rev.

I like to look at the pictures as well as read the text and the featured image in this chapter was similar to (not exactly) this one:

Poskett then shows and discusses Copernicus’ seminal work. This image is from another source, which makes the same conjecture – that Copernicus knew Tusi’s work and that it was important to his theory of motion of planets and stars.