We just started building the largest and most powerful optical telescope ever

Construction began Wednesday, Nov. 11 on what could become the world's largest optical telescope.

The 22-story Giant Magellan Telescope (GMT), now being built in a desert atop a mountain in Chile, could peer deeper into the universe than anything humans have ever built and capture images 10 times sharper than the Hubble Space Telescope.

Astronomers will use GMT to observe planets outside our solar system, watch the birth of new galaxies and stars, study black holes up close, and hopefully unravel some of the mysteries of dark matter and dark energy, which together make up 95% of the universe.

GMT is part of the Carnegie Institute of Science Las Campanas Observatory in the Atacama Desert in Chile. The area's thin, dry air makes it one of the most pristine star-gazing spots on Earth.

The mirror of the telescope will span 85 feet across, but since it's physically impossible to build a mirror that large, engineers are making seven smaller mirror segments and arrange them in a circle.

The finished product will look something like this:

Each mirror segment spans 27 feet and weighs 17 tons - about the weight of three killer whales - according to the GMT Organization.

The mirrors must be absolutely flawless, or the telescope will return fuzzy and distorted images. It takes a full year to cast and cool one of the segments, plus three more years of meticulous smoothing and polishing at the Richard F. Caris Mirror Lab in Arizona to get the finish just right:

Here's one of the mirrors shortly after it was cast and cooled - it's enormous next to the team that worked on it:

If all goes according to plan, GMT will switch on in 2021 and be fully operational by 2024. Then astronomers can start observing parts of space that we've never seen before.

"We don't know what discoveries await us," astronomer Wendy Freedman said in a video about GMT. "That's part of the excitement of building this new telescope."