It has been said that "behind every great computer there is a great memory". As with most sayings, of course, this is not the whole story.
Early in the 17th century, Johannes Kepler established, from actual observations of the positions of the planets in the sky, three laws of planetary motion.
This is an account of some elementary aspects of the subject known as "algebraic topology". It investigates the placing of nets on surfaces and Euler characteristics.