Mauna Kea is an enormous, exinct volcano on Hawaii’s Big Island, and one of the best places on Earth to do astronomy (if you ask them, the best one). In fact, the summit of the mountain hosts one of the world’s most renowned observatories. What makes it so special, other than that it looks like this?

Three of the telescopes on Mauna Kea’s summit. In the background, beyond the clouds is Maui (more than 100km away). CC-BY-NC-SA Carmen Romano

For one, it’s fairly close to the equator (20-ish degrees north), so you can see a whole lot of northern and southern sky from there. Like, you can see the North Star and the Southern Cross at the same time.

That’s not so special, so it’s not all: the telescopes atop Mauna Kea are very isolated, so basically zero light pollution. The closest town (Hilo, a few miles away) has a population of just above 40,000. Plus, local regulations further reduce light pollution.

That somewhat restricts the field. Still, there’s a bunch of isolated places around the Equator.

What’s really special about the telescopes atop Mauna Kea? That they are… well, atop Mauna Kea.

The mountain stands more than 4000 meters above sea level. 4000 fewer meters that light from the stars has to travel through increasingly thick air, which bends and distorts it. Even the little air light has to traverse is bone-dry, so even less distortions.

The light gets blurrier, fainter, and more distorted the more air it has to pass through: better to build observatories high up.

Clouds are not an issue, as they usually lay lower than the summit, which has just 30 rainy days each year (about as many as LA and, you know, it never rains in Southern California).

That’s a tall order to match. There’s only one other place so close to the Equator, isolated, high, and in a desert: the Chilean Atacama desert.

One big drawback of Chile: no hour-and-a-half drive from the observatory can take you to this:

Carlsmith beach in Hilo. CC-BY-NC-SA Karl Wienand

If you want more
  • This is the second installment of cool things I learnt in Hawaii. The first was about lava hair.
  • Putting telescopes on Mauna Kea is actually pretty controversial, since the mountain is sacred in Hawaiian tradition, as this series of podcasts from a local radio tells
  • SciShow Space made a nice video with detailed explanations of how the atmosphere disturbs telescopes (they mispronounce Mauna Kea, though)


Cover photo: mauna kea telescopes at dawn, CC-BY-NC-ND Punchup/flickr


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