Astronomers say they are ready to break ground for the construction of the world's largest telescope after its international backers gave it a financial "thumbs up."

The Giant Magellan Telescope, with an 80-foot-wide primary reflecting surface that will make it one of the biggest optical astronomy instruments ever built, will be erected on a mountaintop in Chile's Atacama Desert.

The international Giant Magellan Telescope Organization backing the GMT has approved the $550 million construction phase, clearing the way for contracts to be awarded to suppliers.

"The GMT will herald the beginning of a new era in astronomy," says Wendy Freedman, chair of the GMTO board of directors. "It will reveal the first objects to emit light in the universe, explore the mysteries of dark energy and dark matter, and identify potentially habitable planets in the Earth's galactic neighborhood."

"The decision by the GMTO partner institutions to start construction is a crucial milestone on our journey to making these amazing discoveries using state-of-the-art science, technology and engineering," continues Freedman, who is also a University of Chicago professor of astronomy and astrophysics.

In preparation, a flat area the size of four football fields has been cleared on the summit of a ridge in Chile's Las Campanas Mountains, home to several other world-class telescopes.

The $550 million from GMTO represents roughly half of the predicted $1 billion price tag of the telescope.

The GMT, which will be housed in a giant dome 22 stories high, should see first light in 2021 and become fully operational by 2024.

The telescope's main reflective surface will be made up of seven 28-foot mirrors clustered together.

Three of the mirrors are in various stages of being produced, with construction of the other four to begin very soon, says GMT director Pat McCarthy.

"We expect in late 2021, possibly in early 2022, we will put three or four primary mirrors in the telescope, start doing some engineering, start doing some astronomy, and by that point we will have the largest (optical) telescope on the planet by a good margin," McCarthy says.

All seven mirrors should be in the telescope by 2024, GMTO officials say.

The GMT is a worldwide scientific collaboration, made up of institutional partners from the United States, Australia, Korea, Brazil and the host nation Chile.