The top of a mountain is about to make way for the base of what will become the world's largest telescope.

An artist's impression of the E-ELT. Image: ESO/L. Calçada.

Between 5:30pm and 7:30pm British Summer Time (UTC +1), a million tonnes of rock will come off the top of Cerro Armazones, a three kilometre tall mountain in the Chilean Andes, in order to allow the European Southern Observatory to begin work on the European Extremely Large Telescope (E-ELT). Once fully constructed, the E-ELT will sport a 39.3-metre segmented mirror enclosed in a giant dome 74 metres tall and 86 metres wide. Huge doors will split apart to expose the telescope to the night sky, while the dome itself will be able to rotate at the rate of two degrees per second. The E-ELT will dwarf today's generation of observatories – by way of comparison the largest telescope in the world today is the 10.4-metre Gran Telescopio Canarias in the Canary Islands.

"The E-ELT will allow astronomers to reach deeper into space, further back in time and more intimately into the workings of the Universe than any other visible to infrared telescope ever built", says Dr Aprajita Verma, Deputy Project Scientist for the UK E-ELT project at Oxford University. "From probing the first galaxies that formed in the Universe, to studying extra-solar planets and looking for signs of life, we can expect break through advances and new discoveries with the E-ELT."

Looking up at the summit of Cerro Armazones, which is about to become 40 metres shorter. Image: ESO/S Brunier.

The E-ELT is being funded by 15 countries around the world, including an #88 million investment by the United Kingdom towards the total £843 million (1.055 billion euros) cost.

You can watch the top 40 metres being explosively removed from Cerro Armazones, signalling the beginning of construction work, via http://new.livestream.com/ESOastronomy. Work is expected to continue for nine years, with the E-ELT scheduled to become operational in 2023.