The Observatories at Mauna KeaEleven research stations sit atop Mauna Kea. This is the best place to look at stars in the world. Mauna Kea means "white mountain" in Hawaiian. This mountain is a dormant volcano on the island of Hawaii. It is the highest point in the Pacific Basin. It is also the highest island-mountain in the world. Mauna Kea rises 9,750m from the ocean floor. It reaches an altitude of 4,205m above sea level. Its summit is above 40% of the Earth's atmosphere.The atmosphere above Mauna Kea is extremely dry and clear. This is due to a cloud layer that floats below the summit. These clouds isolate the upper atmosphere from the lower moist maritime air. This ensures that the summit skies are pure and dry. The clouds keep the air around the summit free from pollutants.This clarity makes Mauna Kea an ideal place for studying the stars. The number of clear nights is the highest in the world. The seeing factor is also very high here. Another factor that makes the stars so clear is the mountain's distance from city lights. A strong island-wide lighting law ensures an extremely dark sky.The Astronomy Precinct on Mauna Kea was established in 1967. The Astronomy Precinct is located on protected land. This land is protected because of its sacred place in Hawaiian culture. This precinct was built to be an international center for astronomers to come and study stars.The dorms for scientists are located below the summit. They are at about 3,000m above sea level. A visitor information station is located a hundred meters further below. Scientists and other visitors are told to stay at the lower level for 30 minutes. They do this to acclimate themselves before reaching the summit. This prevents altitude sickness.Twelve telescopes are located at the summit. They are funded by companies and agencies of various nations. The University of Hawaii controls two telescopes. Two twin telescopes are run by the Keck Observatory. Subaru owns and administers another telescope. The United Kingdom has an infrared telescope while Canada and France have a joint-effort telescope.  Another is owned and operated by California Technical University. The groups that make up this effort help mankind better understand outer space.Based on the passage, which of the following most accurately explains why visitors must pause at the lower level before reaching the summit...