IN ARIZONA, where the Vatican Observatory has its main telescope, the months of July to September are noted for the “monsoons”, intense thunderstorms that often arrive around sundown. Obviously the rain and clouds prevent any use of the telescope. The nearby lightning also means that all our electronics have to be carefully shut down and stored. The observatory, after all, is located in a large metal building on the top of a mountain. Instead, during this time the telescope is handed over to the engineers for upgrades and scheduled maintenance.

Our telescope mirror is a six-foot-wide parabolic dish of glass covered with a thin layer of highly reflective aluminium. The light from a distant star hits this primary mirror, is focused upwards to a smaller secondary mirror, and then directed down through a hole in the centre of the primary to our electronic camera. Every summer, a year’s accumulation of dust and dead moths needs to be washed off the primary mirror’s surface; handily, the sloping sides of the mirror direct the dirty water down the hole in the centre.