- NGC 457 is an open cluster within our own Milky Way galaxy. It is over 7,900 light years from Earth, so the photons from it reaching your eye in a telescope left that cluster about the time copper was first being used in the Middle East. The estimated age is about 21 million years, making it one of the younger star clusters in our galaxy. Here is how to locate it.
- Category Theory (plato.standford.edu)
Category theory has come to occupy a central position in contemporary mathematics and theoretical computer science, and is also applied to mathematical physics. Roughly, it is a general mathematical theory of structures and of systems of structures.