Construction began in Chile on Friday on the European Extremely Large Telescope, which when completed will be the world's largest optical telescope, some five times larger than the top observing instruments in use today.
The size of the ELT has the potential to transform our understanding of the universe, say its backers, with its main mirror that will measure some 39 meters (43 yards) across.
Located on a 3,000 meter-high mountain in the middle of the Atacama desert, it is due to begin operating in 2024.
Among other capabilities, it will add to and refine astronomers' burgeoning discoveries of planets orbiting other stars, with the ability to find more smaller planets, image larger ones, and possibly characterize their atmospheres, a key step in understanding if life is present.
"What is being raised here is more than a telescope. Here we see one of the greatest examples of the possibilities of science," said Chilean President Michelle Bachelet in a speech to mark the beginning of construction at the site.
The dry atmosphere of the Atacama provides as near perfect observing conditions as it is possible to find on Earth, with some 70 percent of the world's astronomical infrastructure slated to be located in the region by the 2020s.
The ELT is being funded by the European Southern Observatory, an organization consisting of European and southern hemisphere nations. Construction costs were not available but the ESO has said previously that the ELT would cost around 1 billion euros ($1.12 billion) at 2012 prices.