Rubin Observatory and Seeing Monitor

The Rubin Seeing Monitor in the foreground, with the Vera C. Rubin Observatory behind it, on Cerro Pachón in Chile.

There is a little telescope in the Rubin Seeing Monitor's dome on Calibration Hill. It's called a DIMM, or Differential Image Motion Monitor. Looking at bright stars, it tracks the motion of the stellar image due to the Earth's turbulent atmosphere. This gives the team an independent measure of the quality of images arriving at the telescope.