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 aerial view of the Earth, you can tour the solar system, and other up to 10 million stars, or even outside the Milky Way constellation.