Aluminising a Telescope's Mirror

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 the Australian Astronomical Observatory (AAO) remove the 16 tonne mirror from the telescope’s support structure and prepare the mirror for aluminising.  First, they strip off the old reflective coating, then prepare and polish the glass surface, and finally secure the mirror inside the large vacuum chamber metal tank for aluminising. 

The smooth glass surface is covered with a few grams of aluminium, spread out in a layer only 100 atoms thick.  

To see the SHORT (3 minute) preview of this film, watch the TRAILER version of Aluminising here:


Making of the Film

The footage for this film was shot on location at the Anglo-Australian Telescope using a Canon 5D Mark III and 6D by Andy Green. The aerial footage of the Anglo-Australian Telescope building was filmed by Peter Poulos of iTelescope. Some additional archive footage of the telescope was filmed by Fred Kamphues  and night sky sequences were obtained by AAO/MQ Astronomer Angel Lopez-Sanchez. The music was performed by the Czech National Symphony Orchestra. The pieces are “Peer Gynt Suite No. 1, Op. 46 - IV. In the Hall Of The Mountain King” composed by Edvard Grieg and “In The Steppes of Central Asia” composed by Alexander Borodin. The teaser version also includes “The Planets, Op. 32 - IV. Jupiter, the Bringer of Jollity” composed by Gustav Holst and performed by the Skidmore College Orchestra. All music is public domain, courtesy of Musopen.


The “ritual” at other observatories

See how other telescopes aluminise their mirrors:

ESO’s Very Large Telescopes :

Palomar Observatory’s Hale Telescope:

The Canada-France-Hawaii Telescope: