Astronomers planning on building the world's biggest telescope high in the Andes Mountains in Chile say they've secured official go-ahead for its construction.

The official green light by the project's executive council means the giant instrument is on track to begin observing the heavens sometime in 2024, officials of the European Southern Observatory said.

The European Extremely Large Telescope (E-ELT), to be built on the summit of Cerro Armazones in Chile's Atacama Desert, will possess a giant light-collecting surface 128 feet across.

The E-ELT received initial approval in 2012, with the proviso that initial construction contracts worth almost $2.5 million would be awarded only when 90 percent of the estimated $1.3 billion funding needed to construct the giant facility had been secured.

That threshold was reached in October as Poland agreed to join the European Southern Telescope and joined in funding the project.

That led the ESO Council, the organization's governing body, to approve Phase 1, the awarding of the first contracts, which will occur in late 2015.

That phase will see the construction of the observatory structure and its dome, expected to take 10 years.

Although the telescope itself will not be complete by then, most of its giant mirror will be in place, allowing astronomers to begin some preliminary observations as the rest of the main mirror and optics system are being finished as part of Phase 2, ESO officials said.

"The decision taken by Council means that the telescope can now be built, and that major industrial construction work for the E-ELT is now funded and can proceed according to plan," said Tim de Zeeuw, ESO's director general. "There is already a lot of progress in Chile on the summit of Armazones, and the next few years will be very exciting."

The E-ELT is just one of three giant telescopes in the planning stages.

The Giant Magellan Telescope, set to be built at the Carnegie Institution's Las Campanas Observatory on another Chilean mountain top, will combine seven mirrors into an 80-foot light-collecting surface with an intended "first light" date of 2012.

And the Thirty Meter Telescope will turn its own 98-foot light gathering surface toward the heavens from atop Hawaii's Mauna Kea volcano sometime in 2022.

However, by dint of its size, the E-ELT is "the most powerful of all the extremely large telescope projects currently planned," de Zeeuw says, capable of searching for Earth-sized exoplanets and the delving deep into nearby galaxies.

 "The next few years," he says, "will be very exciting."