Mauna Kea ("White Mountain") is a dormant volcano on the island of Hawaii, the largest and southernmost of the Hawaiian Islands. It is located about 300 km (190 miles) from the capital city, Honolulu, on the island of Oahu. The highest point in the Pacific Basin, and the highest island-mountain in the world, Mauna Kea rises 9,750 meters (32,000 ft) from the ocean floor to an altitude of 4,205 meters (13,796 ft) above sea level, which places its summit above 40 percent of the Earth's atmosphere. The broad volcanic landscape of the summit area is made up of cinder cones on a lava plateau. The lower slopes of Mauna Kea are popular for hunting, hiking, sightseeing, and bird watching in an environment that is less hostile than the barren summit area.

The summit of Mauna Kea on the Island of Hawaii hosts the world's largest astronomical observatory, with telescopes operated by astronomers from eleven countries. The combined light-gathering power of the telescopes on Mauna Kea is fifteen times greater than that of the Palomar telescope in California -- for many years the world's largest -- and sixty times greater than that of the Hubble Space Telescope.

Mauna Kea is unique as an astronomical observing site. The atmosphere above the mountain is extremely dry -- which is important in measuring infrared and submillimeter radiation from celestial sources - and cloud-free, so that the proportion of clear nights is among the highest in the world. The exceptional stability of the atmosphere above Mauna Kea permits more detailed studies than are possible elsewhere, while its distance from city lights and a strong island-wide lighting ordinance ensure an extremely dark sky, allowing observation of the faintest galaxies that lie at the very edge of the observable Universe. A tropical inversion cloud layer about 600 meters (2,000 ft) thick, well below the summit, isolates the upper atmosphere from the lower moist maritime air and ensures that the summit skies are pure, dry, and free from atmospheric pollutants.

There are currently thirteen working telescopes near the summit of Mauna Kea. Nine of them are for optical and infrared astronomy, three of them are for submillimeter wavelength astronomy and one is for radio astronomy. They include the largest optical/infrared telescopes in the world (the Keck telescopes) and the largest submillimeter telescope in the world (the JCMT). The Submillimeter Array is currently nearing completion, while the westernmost antenna of the Very Long Baseline Array (VLBA) is situated at a lower altitude two miles from the summit.

Mauna Kea is situated on the Big Island of Hawaii. It can be reached from Route 20--the narrow and winding Saddle Road, so named because it runs between the two major volcanic mountains, Mauna Loa and Mauna Kea, at an elevation of 2,000 m (6,600 ft). A paved road leaves the Saddle Road at Mile 28 and winds its way up to the lower slopes of Mauna Kea to the Visitor Information Station (VIS) at the Onizuka Center for International Astronomy (OCIA), which is the mid-level altitude acclimatization center for scientists and technicians. The distance from Hilo to the OCIA is 34 miles (55 km), with the average travel time being 1 to 1-1/2 hours.

If you would like to visit Mauna Kea Observatory it is recommend that you begin at the Visitor Information Station of the Onizuka Center for International Astronomy at the 10,000-foot level on the Mauna Kea access road. At the center you can learn about the mountain, the telescopes, and the Universe, buy souvenirs and view the stars after dark through the our portable telescopes.

You can also drive to the 14,000-foot summit of Mauna Kea to view the domes of the main observatory itself, but you need to be aware that;

• Ordinary vehicles cannot cope with the steep, unpaved road; you will need to obtain a four-wheel drive vehicle, or take a commercial tour
• There are no opportunities to "look through" the telescopes at the summit, and visitors are not allowed at the summit after dark.
• The road up the mountain can be dangerous, particularly in bad weather.
• The high altitude of the observatory carries serious health risks and routinely impairs physical and mental activity.
• Only one observatory (Keck) has a visitors' gallery from which the telescope may be viewed during the day.

The road above the OCIA to the Mauna Kea Observatories is unpaved, rough, steep, winding, and dangerous. Only four-wheel-drive vehicles are permitted above the OCIA. The road can be traversed in about half an hour in good weather, but extreme caution must be exercised when driving it, particularly on the descent. Use low gear and be on the lookout for slide areas and for loose gravel. Do not drive over 25 mph. Use headlights if it is foggy. The switchback section of the road above OCIA is particularly hazardous during the hour after sunrise and the hour before sunset, because of the low elevation of the Sun - in several sections of the road, you must drive directly towards the Sun, so it is very difficult to see oncoming traffic

Visitors to Mauna Kea should prepare themselves for severe weather, especially during the winter months, when heavy storms commonly deposit several feet of snow. Minimum nighttime winter temperatures at the summit are around -4 degrees Celsius (25 degrees Fahrenheit); maximum daytime temperatures are about +4 degrees Celsius (40 degrees Fahrenheit), but wind chill and the high altitude can make it seem much colder. Between April and November the weather is milder, with daytime temperatures varying from freezing to almost 15 degrees Celsius (60 degrees Fahrenheit).

Altitude sickness

• At the summit elevation of 13,796 feet (4,200 m), the atmospheric pressure is 40 percent less than at sea level. Less oxygen is available to the lungs, and acute mountain sickness is common. Symptoms include: headaches, drowsiness, nausea, shortness of breath, and poor judgment.
• The intensity of these symptoms may be lessened by spending at least a half hour at the Visitor Information Station (altitude 9,200 feet or 3,000 m) before traveling to the summit..
• Children under 16, pregnant women, and people with respiratory, heart, or severe overweight conditions are advised not to go higher than the OCIA Visitors Information Station.
• Scuba divers must wait at least 24 hours after their last dive before traveling to the summit.

High altitudes can also cause the life-threatening conditions pulmonary edema (fluid in the lungs) and cerebral edema (fluid on the brain). Descend immediately if any of these symptoms appears:

• severe headaches,
• vomiting,
• breathing difficulties,
• coughing,
• blue lips or fingernails,
• disorientation,
• extreme drowsiness that may lead to coma.
• Drink Plenty of Water

The summit is usually extremely arid. To prevent dehydration, you should drink plenty of water prior to and during your visit to the summit of Mauna Kea.

Sunburn and Eye Damage

The summit is above much of the atmosphere that blocks the sun's ultraviolet radiation. This presents a risk of serious sunburn and eye damage, particularly when there is snow on the ground.

Impaired Judgment

High altitude causes impaired reasoning and drowsiness. Alcohol will further impair judgment and driving abilities.

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