A Klein bottle can't hold any liquid because it doesn't have an inside. How do you construct this strange thing and why would you want to?

How to write a sum that's infinitely long.

What is 1-1+1-1+1-1+...? How infinite sums challenge our notion of arithmetic.

Here's an easy game that leads you straight to an unsolved question in maths.

How to write down unimaginably large numbers using just a few symbols.

A little trig helps to find the relative distance to the Sun and Moon.