Aluminising the Anglo-Australian Telescope

One of the most important “secret rituals” of an astronomical observatory is the aluminising of the telescope’s mirror. The 4-metre primary mirror of the Anglo-Australian Telescope (AAT) is a huge chunk of finely polished glass-ceramic that has been coated with a thin layer of aluminium to create the reflective surface. Over time, the surface of the mirror collects dust and dirt from the air, and from birds and bats flying, occasionally leaving a dropping or two! So once a year, the technicians at