NEAR THE SUMMIT OF MAUNA KEA, Hawaii—Bill Healy stares into the primary mirror of the largest telescope in the world, and, for a second, he pauses. Even now, after nearly two decades of looking after this titanic instrument on top of a mountain, the immensity of the mirror still arrests him. “It sure is a hell of a view,” Healy marvels. “A hell of a view.”

It is. We’ve just ascended the tallest mountain in the Hawaiian islands, Mauna Kea, to see the pair of 10-meter Keck Telescopes, the largest and most powerful optical telescopes in the world. Hawaii lies 4,000km away from the closest continent, North America, making this the most remote archipelago on Earth. With clear skies, therefore, Mauna Kea has arguably the best “seeing” of any telescope site in the world.

The combination of big mirrors and dark skies has proven nothing short of revelatory. Since the first of the two Keck telescopes began observing the heavens in 1993, astronomers have used the instruments to discover dark energy, find outer Solar System objects that led to Pluto’s demotion, and more. On a given night, an astronomer might point a telescope toward volcano eruptions on the Jovian moon Io or study faint galaxies at the edge of the visible universe.