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.

But increasingly, the mountain’s fair skies are clouded with controversy. Native Hawaiians dispute the right of outsiders to build large telescopes on their sacred mountain, and a proposal to build a much larger instrument, the Thirty Meter Telescope (TMT), on Mauna Kea has galvanized the activists as never before.

Healy speaks with a Northeasterner's accent. An improbable path led him from a career in the US Marines to “retirement,” to becoming a middle school teacher in Hawaii, and to, finally, landing a job two decades ago as a caretaker for the telescopes. He has difficulty squaring his love for this facility, the mountain, and the groundbreaking science they enable with the antagonism bubbling up from the valley below.

“Up until a few years ago, all of the telescopes up here pretty much operated under the radar,” he explained during a tour of the facility. “People either didn’t care or they really didn’t know what was going on. But because of all the attention from the TMT, it’s kind of painted us all with the same brush. Where you normally would be happy to wear your Keck crew t-shirt while shopping at Costco, you may not do that today.”

For some natives, the majestic domes that house huge telescopes on top of the mountain seem more like pimples, best popped. As tolerance has turned to tension, legal actions have begun moving through the Hawaiian court system. No longer is it inconceivable that the magnificent telescope Healy and I are admiring, which has in no small way remade almost the entire field of astronomy, might one day be gone.

The site

Gerard Kuiper, who counted Carl Sagan among his students, is probably the greatest modern planetary scientist. He correctly predicted the composition of Saturn’s rings (ice) and that planets in our Solar System formed when a large cloud of gas condensed. He also proposed the existence of a now-eponymous belt of minor planets outside the orbit of Neptune, and he “discovered” Mauna Kea for astronomers.

After the University of Hawaii dedicated the Haleakala Observatory on Maui to study the Sun in 1964, Kuiper—then at the Lunar and Planetary Laboratory at the University of Arizona—visited. He wanted to determine whether the Maui mountain, topping out at 10,000 feet, might also be suitable for planetary observations. It turned out not to be high enough to remain consistently above the regional inversion layer, so many nights were too cloudy for observations.

However, as Kuiper looked across the Maui Channel to the Big Island, he could see Mauna Kea looming 4,000 feet higher, above the clouds. Soon, Kuiper had persuaded the governor of Hawaii, John Burns, to provide funds to bulldoze a road and construct a small telescope for testing. The site was superb. By 1970, the University of Hawaii had built a 2.2-meter telescope on Mauna Kea. More would soon follow.

Eastern trade winds blow across the islands and, with no other mountains downwind, there is little turbulence. At the peak, water vapor levels are very low relative to most observatories. The inversion layer, too, is a boon at 14,000 feet. During the nighttime hours, clouds sink as the air temperature cools. Even though lights from towns along Hawaii’s coast don’t present that much of a problem, any light pollution from Hilo, Kona, and Waikoloa is often shrouded by these clouds.