The race to build a super-large ground telescope is likely down to two competitors

I have been writing about the Giant Magellan Telescope for a long time. Nearly two decades ago, for example, I wrote that time was "running out" in the race to build the next great optical telescope on the ground.

At the time the proposed telescope was one of three contenders to make a giant leap in mirror size from the roughly 10-meter diameter instruments that existed then, to approximately 30 meters. This represented a huge increase in light-gathering potential, allowing astronomers...