Four thousand years ago, a volcano erupted in a remote and isolated region of the Pacific Ocean. Today, that now-dormant volcano is the world's highest island mountain. It is also one of the best places anywhere to study the heavens, because the air is clear, dry and relatively free from atmospheric pollutants. Astronomers from around the globe come to the observatory based here to explore the universe. Others come during the day for a look around.

Astronomers must compete for observation time on Mauna Kea. Tourists are welcome anytime to hike up the 4,205-meter summit or to join a guided caravan tour that departs from the Mauna Kea Visitors Center, about two-thirds of the way up the peak. This is where guide Erik West hands out some basic advice: "You do need a 4-wheel drive vehicle and there are some health and safety issues," he says. "You cannot have any heart or respiratory problems, be under 16 years of age, or have scuba dived in the last 24 hours."

Erik West readies drivers for the trek up telling them to put their 4-wheel drive vehicles in low. One behind the other, the cars follow a steep gravel road that switches back and forth during the 45-minute drive. The sedges gradually give way to a barren moonscape of lava rock and cinder cones.

As we reach the summit and park our vehicles, the complex of domed observatories suddenly loom like a garden of giant mushrooms.

The air up here is cool as we walk toward the buildings, but our guide warns us that the air can also make you sick because it has 40% less oxygen than at sea level. "It has varying effects on people," he says. "If you start to feel dizzy, nausea, let someone know. We do carry oxygen with us." But he, adds, "If you do need to have oxygen, you do have to go down. That is the rule."

The first large telescope was built on Mauna Kea in 1970. Since then, others followed. Today there are a total of 13 groups of observatories. "One of them - SMA (Submillimeter Array) - is actually (comprised of) eight different telescopes that operate together," Eric West says. "There are 11 different countries that are involved with the telescopes up here and various universities." The 10-meter Keck telescopes are the biggest. "The reason that they keep getting bigger and bigger," Eric West explains, "is that we want to be able to collect as much light as possible up here. So, the bigger you are, the more light you can see."

The twin Keck I and Keck II are the world's largest optical and infrared telescopes. Their mirrors are divided into 36 hexagonal segments, which work together as a single piece of reflective glass. During the day Keck I is a sleeping giant of steel beams and silent gears closed inside a protective shell.

"The dome weighs about 700 tons protecting this thing. It's ?about 10 stories to the top of the dome and the whole mirror structure is about 8 stories (tall)," Erik West says, explaining the real action begins at sundown. "The dome will open up and start rotating to where they need it and the mirror rotating to where they are going to be observing. And, throughout the night, if it is following an object, it will be moving very slightly to follow it as it moves across the sky. But there won't be anyone in here generally. They will be in the control rooms staying warm."

This is where Rolf Kudritzki works. He is the director of the Institute for Astronomy, which manages Mauna Kea. Over the years, astronomers have discovered new moons around Jupiter, taken pictures that help measure the expansion of the universe and have observed hundreds of small objects orbiting the Sun past the orbit of the planet Neptune.

He says astronomers also look for signs of life in the universe beyond our solar system. "We believe that the existence of planetary systems orbiting stars is a necessary ingredient for the development of life," Mr. Kudritzki says, adding that some of the planets recently discovered orbiting distant stars were spotted with Mauna Kea telescopes.

Each movement, each gear, each wheel guiding these massive telescopes is remotely controlled. Astronomers review the data - not from an eyepiece - but from a desktop computer.

Rolf Kudritzki says - despite such sophisticated equipment - not every astronomer at Mauna Kea finds what they are looking for. "Because in modern astronomy," he says, "we look at things that are barely detectable, faint at the margin of feasibility all the time because we are just pushing the frontier of our detections further and further away. So it is not always clear that such an observation will be successful."

While space telescopes like the Hubble work outside the earth's atmosphere to capture undistorted, finely detailed views of the cosmos, their relatively small size limits their light collecting power. Rolf Kudritzki says land-based observatories can often provide more details about the physical properties of celestial objects. "You could determine, for instance a chemical composition out of the spectrum, the distance, the size, the mass, etcetera."

Rolf Kudritzki says that compared to space telescopes, land-based observatories like those atop Hawaii's Mauna Kea provide astronomers with less expensive observing time and a more diverse array of tools for observing the heavens. Mr. Kudritzki predicts confidently that the Mauna Kea observatories will continue to complement earth orbiting telescopes for many decades to come.