Aluminising the Anglo Australian Telescope

One of the most important secret rituals of an astronomical observatory is the aluminising of the telescopes mirror. The 4metre primary mirror of the AngloAustralian Telescope (AAT) is a huge chunk of finely polished glassceramic 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