The Extremely Large Telescope (ELT) will be the world's largest optical telescope. The telescope is being built by the European Southern Observatory (ESO). The ESO is made up of 16 countries which includes the UK and Ireland. The ELT is due to be complete at the end of 2027. 

The ELT will observe visible and infra-red wavelengths of light. The 40-metre main mirror will collect 100 million times more light than the human eye. Its total mass will be 3000 tonnes!

The ELT is in the Atacama Desert in Chile. It is over 3000 metres above sea level. This dry and high spot provides the best conditions for an optical telescope. The air will be as still as possible which stops images looking blurry.

The ELT is being built to study exoplanets, galaxies, black holes, and star formation. It will be able to make detailed images of the first galaxies, and to follow their evolution through time. Scientists may also be able to use the ELT to measure the rate of the Universe's expansion. This would be a huge step in our understanding of cosmology.

The ELT will have 5 mirrors. Three of these mirrors are curved, the other 2 are flat. The curved mirrors will provide excellent images over a wide angle of sky. The flat mirrors will provide adaptive optics and image stabilisation tools. These tools will let the ELT take really clear images of stars from Earth. Despite being a ground-based telescope, it will be able to make images 16 times sharper than the Hubble Space Telescope.