This is a collection some of the expository notes that I have written, they range in topic, some closer to my research and some farther away. As opposed to posts in "Mathematical Diversions", posts here are intended to be read by other people. I welcome comments and corrections.

We introduce the Kodama vector field for rotationally symmetric space-times and its relation to gravitational red-shift.

I've just spent much too long puzzling over the geometric formalism of a paper of Lazar and Hehl, so I figure I'll write a little …

We give a proof of the irrationality of π.

We explain how to conformally compactify Lorentzian manifolds.

Lecture notes on a fake derivation of the Kerr metric from the Schwarzschild metric, based on lots of hindsight.