Altitudes of the Sites of Optical Observatories

The selection of the best sites for future optical telescopes in China is under consideration and some discussions on the altitude of a site are presented in this paper. The old observatories which had been funded before 1950s, as a general rule, are located at the altitudes not over 2000m. Most of the new observatories with large telescpes, which have been bult up in recent 30 years, are located at the places of 2000m or 3000m above sea level. The heights of most of the places for site testing in 1980s are also within the range from 2000m to 3000m. Mauna Kea, with an elevation of 4200m, is the highest observatory site in the world, where the population density is only seven per square kilometer. This site is near the equator and the weather at the summit is remarkably mild. In Yunnan Province, China, the hopeful altitude of thesite for a future optical telescope may be between 2500m and 4000m.