Earlier quoted context omitted.
The starting principle is simple, then the scientists build a lot of clever stuff, the telescopes on Earth, the telescopes on the satellites and the remote controlled radio telescopes... Parallax. Telescopes. https://medium.com/starts-with-a-bang/how-do-we-know-the-dis... "the same math that enables you to hold your thumb at arm’s length, close one eye and then switch eyes and watch your thumb appear to shift, allowe…
>"math that enables you to hold your thumb at arm’s length" This person seems to be using a non-standard definition of "math".
The clearer formulation would probably be: the same effect that we see by closing one then another eye is seen from the Earth when we look at the stars months apart, and the formulas that could be derived using the distance of your eyes and your arm can also be applied to the cosmic distances.