The dry air is really good for telescopes, and also, the cloud cover is below the summit of these mountains so that the telescopes have about 300 days of clear skies.
干燥的空气对望远镜的观测是很有好处的， 同时，在高山地区的云层覆盖率也也比较低的。 这样这些望远镜 就有大约300天的晴天来观测了。