The largest optical telescope in the world

When building astronomical telescopes bigger is often better. And this means that there's often a race to build the next big telescope that will push our view of the Universe further and deeper. But before we obsess about the next big thing, lets take a moment to consider the current holder of the World's Largest Optical Telescope crown, the Gran Telescopio Canarias, which has a mirror stretching 10.4 m from side to side!

The Gran Telescopio Canarias on the summit of La Palma
(Credit: GTC)

The GTC, as its usually known, is the largest optical telescope in the world. It's based at the Roque de Los Muchachos Observatory at the summit of the island of La Palma, an excellent site for astronomy as it is both high up (above the clouds) and also very dry. It's owned and operated by several astronomical institutions in Mexico, the United States, and primarily Spain.

The 10.4 m mirror of the Gran Telescopio Canarias,
made up of 36 hexagonal, smaller mirrors
(Credit: GTC)

The telescope's mirror isn't a single mirror but 36 hexagonal mirrors that fit together to produce a telescope with an equivalent diameter of 10.4 m. Thanks to their extremely precise alignment all the segments reflect light as if they were a single mirror. This is a common technique in astronomy for making really big telescopes, as it is a lot easier to make multiple medium-sized mirrors than one very large mirror. As you'd imagine for a telescope of this size, the GTC took over 6 years to build!

The telescope was completed in 2008 and saw its first scientific observations in 2009. Since then the telescope has done some amazing work in all areas of astrophysics using a selection of instruments, including both imaging cameras and spectrographs, that can operate throughout the optical, the near-infrared and the mid-infrared.

The telescope sits close to the summit of La Palma at a site well known for its dry weather and good observing conditions. There are many telescopes clustered together at the observatory here, owned and operated by astronomical institutions across Europe.

I've had the pleasure of visiting this observatory many times for work and it is a beautiful place, well worth visiting if you get a chance, and particularly if you can stay for sunset (or get up early enough for sunrise!).

Sunset view from the summit of La Palma showing the Gran Telescopio Canarias (right) and the
Italian Telescopio Nazionale Galileo (left) above the clouds (Credit: Nick Wright)