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October 1, 2020


All about GTC

How will it work?

The mirrors

Secondary mirror

Essentially, a telescope is an optical system that can gather light photons and direct them on to a plane called the ‘focal plane’ or ‘focus’.

The secondary mirror receives light from the primary mirror and deflects it to the Cassegrain focus or the tertiary mirror, from where it is deflected on to the Nasmyth and folded Cassegrain foci.

In some telescopes the secondary mirror has to be changed whenever work alternates between visible and infrared light. This changeover is not only very expensive but also loses observing time because it can take more than a day.

The GTC’s secondary mirror will be able to work with both types of light. It will be made of beryllium substrate, which is much lighter and tougher than ceramics, coated with a layer of nickel. Quasi-hexagonal in shape (adapted to the shape of the primary mirror) and with a convex hyperboloidal surface, the secondary mirror will weigh just 55 kg, have an area no greater than 1.2 m and will feature state-of-the-art technology.

The secondary mirror’s complex movement and control mechanisms will compensate for vibration and, most importantly, will measure variations in the thermal infrared range (the longer wavelengths in the infrared spectrum). To perform this technique, called ‘chopping,’ the secondary mirror will oscillate rapidly, as though forever dancing to the music of the spheres.