A new European telescope destined to become the world's biggest eye on the sky has been given the green light.
Plans to build the £900m European Extremely Large Telescope (E-ELT) were approved in principle at a meeting in Garching, Germany.
Due for completion in 2022, the E-ELT has a main mirror spanning 39 metres, making it the largest optical telescope in the world.
It will have the power to obtain direct images of planets in orbit around distant stars - perhaps even Earth-like worlds.
The telescope will also allow astronomers to study the first galaxies that formed after the Big Bang.
The decision was taken by the ruling Council of the European Southern Observatory (ESO), an international collaboration of 15 member states.
It still has to be ratified by four ESO members, including the UK.
Assuming final permission is given, preparation work on the telescope site on top of the Cerro Amazones mountain in northern Chile should begin later this year.
Professor David Southwood, president of the Royal Astronomical Society, said: "We urge the UK Government to approve our involvement in E-ELT as soon as possible, so that British scientists and engineers can take a full role in what is set to be one of the most exciting scientific projects of the 21st century.
"The decision is good news not only for the UK but for astronomers across Europe. It is good to see Europe boldly going where others have yet to venture. E-ELT will help us answer some of the fundamental questions about the universe, from the nature of planets around other stars to the early history of the cosmos.
"World-leading projects of this kind inspire us all and are hugely effective in bringing young people into careers in science and technology."
To approve the start of the programme, at least 10 ESO member states had to vote in favour.
At the council meeting, Austria, the Czech Republic, Germany, the Netherlands, Sweden and Switzerland all said yes to the plans.
Representatives of four other states, the UK, Belgium, Finland and Italy, pledged provisional support subject to confirmation by their governments.
Major funding for the E-ELT has to be committed within the next year, and early contracts for the project have already been placed.
Shortly before the meeting, a contract was signed for a detailed design study of the telescope's state-of-the-art adaptive mirror.
ESO director general Tim de Zeeuw said: "This is an excellent outcome and a great day for ESO. We can now move forward on schedule with this giant project."