celestia是一个免费的开放源代码天文类软件，通过它你不仅可以鸟瞰地球，还可以畅游太阳系，以及其它多达10万颗星，甚至是银河系以外的星座。-celestia is a free open source software astronomy class, through which you can not only overlooking the earth, you can tour the solar system, and other up to 10 million stars, or