303 | AMA | February 2025

6663.899 - 6689.586 Sean Carroll

The angular distance you just measure by taking a picture of the galaxies on the sky. So you have accurate measure of where the galaxies are in the sky and a distorted measure of where they are along your line of sight. So you take what should be a relatively spherical blob of galaxies in a cluster, and when you plot it in what you think is position in space, it is elongated in the direction of u.