Sen—A new telescope that will be the world's largest optical instrument has come a step closer after being given the green light by European member states.

Full approval for the European Extremely Large Telescope was given after votes by ten nations in favour were confirmed at a meeting of the European Southern Observatory's ruling Council.

However, ESO still awaits commitments from all the countries to fund this giant eye on the sky. So far 60 per cent of funding, or 615 million euros, has been committed to the project. ESO says construction will begin in Chile once 90 per cent of funding is pledged.

The site for the instrument has already long been chosen. It will stand on the 3,060-metre high Cerro Armazones mountain peak in the Atacama Desert. I visited the site last year following a thrilling ride along tracks and rough, boulder strewn terrain that looked more like Mars.

The E-ELT will have a mirror 39.3 metres wide (43 yards) and be far more powerful than any other ground-based instrument. The dome housing it will be nearly as tall as London's Big Ben and cover an area the size of a football stadium. Engineers will have to blast the top off the mountain to build it.

The telescope's sensitivity to visible and infrared light will be tens of times greater than any present telescope and will allow astronomers to peer back billions of years in time to the first galaxies to form in the early universe nearly 14 billions years ago.

It could also help solve the mysteries of two little understood forces in astronomy, dark matter and dark energy, and so help explain how the Universe evolved and is expanding.

A cutaway illustration shows a preliminary design for the E-ELT. Credit: ESO

Astronomers say the telescope, which should be operating by 2020, could also help to tell us if we are alone in the Universe. It will be powerful enough to image planets around nearby stars and help identify Earth-like rocky worlds that might be home to life.

One early target could be Alpha Centauri, the closest star system to us, which was found by ESO to have a planet earlier this year. Astronomer Professor Isabelle Baraffe, of the UK's University of Exeter, said that the discovery of one planet there meant there were likely to be more.

She added: "Because the star is so close and so bright, it will be possible to make follow up observations, for example with the E-ELT, to characterise the atmosphere of this planet and possibly others to be discovered around Alpha Centauri. The next step we will be looking for biosignatures - signs of life - in other planets around the star."

The E-ELT will have a revolutionary design. The primary mirror which collects the incoming light from space consists of almost 800 segments, each 1.4 metres wide, but only 50mm thick. The light will be reflected to a huge secondary mirror 4.2 metres in diameter, bigger than the primary mirrors of any of ESO's telescopes at its first Chilean site La Silla.

Sen writer Paul Sutherland at the E-ELT site in Chile with the VLT on the horizon. Credit: Emily Baldwin

Adaptive mirrors are incorporated into the optics of the telescope to compensate for the fuzziness in the stellar images introduced by atmospheric turbulence. One of these mirrors is supported by more than 6000 actuators that can distort its shape a thousand times per second.

The E-ELT will be the latest major astronomical tool to join a number of observatories operated in Chile by Europe. The Atacama is a favoured location because the dryness and clarity of the air provide exceptional observing conditions.

Apart from those at La Silla, instruments include the Very Large Telescope (VLT) at Paranal, about 20 km away from the E-ELT site, which is actually four giant telescopes, each with an 8.2-metre wide main mirror, that can work separately or together.

Another, called ALMA, short for the Atacama Large Millimeter Array, is an array of dishes, still being added to, that form the highest observatory in the world at 5,000 metres (16,000 ft) on the Chajnantor plateau. They observe the sky together at very short wavelengths which are invisible to the eye.

Astronomers will not need to travel to the E-ELT itself to use it. It will be operated from the same control room at Paranal as the present VLT instruments.