Observatories are built on mountains to raise them above the thick, turbulent lower levels of the atmosphere. In principle, the higher the telescope the better. In practice, the expense of building mountain roads and the severity of high-altitude weather inspires a willingness to compromise. Mauna Kea Observatory in Hawaii, which may be the highest observatory that will ever be built on Earth, stands at nearly 14,000 feet, where gale-force winds are common and the air so thin that higher brain functions are impaired by lack of oxygen. Astronomers quartered halfway down the mountain write themselves childishly simple instructions they hope their muddled brains will be able to obey when they go up to the dome to observe.