Watch How The Massive Mirror Of The Very Large Telescope Is Cleaned


The 8.2m diameter main mirror of Antu, the first Unit Telescope of ESO's Very Large Telescope, is being cleaned using carbon dioxide snow. While the telescope enclosure is maintained extremely clean, the mirrors are exposed to the elements during the observations. Consequently, dust from the desert slowly accumulates over the surface of the mirror, making it less reflective over time. The mirror's surface is so delicate that normal cleaners used for household mirrors are not appropriate for telescopes. Observatories have developed other methods, such as this one using carbon dioxide snow. The tiny CO2 snowflakes in the white plume have a temperature of almost minus 80 degrees Celsius; when they land on the mirror, which is at room temperature, they cause minuscule 'explosions' that detach the dust grains from the surface. The dust then floats away, leaving the mirror clean. The process is nevertheless very delicate: should Alain Gilliotte, the optician performing the cleaning, let the CO2 device touch the mirror, the fragile reflective Aluminium coating would be scratched. Also, hair or cloth lint should stay away from the mirror, which is why the optician is wearing a white suit made of special plastic.  Source: ESO
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Cleaning is not really the loveliest of chores on the planet. It works well for your face or your house but if you have to clean your electronics, it is quite a mess because you can not afford to get a drop of water in there. Washing a car is fine but when the vehicle goes as humungous as an airplane, that too with fragile components, the task is multiplied many folds. Similar efforts go towards cleaning equipment as massive as the Very Large Telescope (VLT) operated by the European Southern Observatory.

Milky Way grazes the tops of the telescopes as it stretches across the sky.
Source: ESO

Located at the Cerro Paranal in the Atacama Desert of northern Chile, the VLT is a combination of four individual telescopes, namely AntuKueyenMelipal, and Yepun. Cleaning the giant mirrors of these telescopes is quite a task, that too in the middle of a desert where there is absolutely no way to avoid dust.

The 8.2m diameter main mirror of Antu, the first Unit Telescope of ESO’s Very Large Telescope, is being cleaned using carbon dioxide snow. 
Source: ESO

ESO officials say, “Every night the huge mirrors are exposed to the atmosphere while uncovered during observing sessions. They gradually accumulate dust and other pollutants that reduce their reflectivity, making them less effective at capturing faint light from the cosmos. So they are regularly removed from the telescope, taken down the mountain to the re-coating facility, cleaned and finally recoated with a thin and highly reflective new aluminium layer.”

The process requires removing the mirror and transferring it to a re-coating plant, and it can take up to eight days. The officials also say that it looks like a simple task, but it actually is quite a tense operation. Pretty cool, isn’t it?

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