bird glide flying over blue sky

>For other uses, see Sky (disambiguation). The sky is (roughly) that part of the atmosphere or of outer space visible from the surface of the earth (or any other planet; see Skies of other planets).). Birds, airplanes, and kites are often considered to fly in the sky. It is difficult to define precisely for several reasons. During daylight the sky has the appearance of an opaque blue surface, but this is the result of the air refracting sunlight. There is no "blue object" above the earth in any normal sense, so it is hard to say what object the sky is. The sky is thus sometimes defined as the denser gaseous zone of a planet's atmosphere. At night the sky has the appearance of a black surface or region scattered with stars. But if we then say that the sky is the entire visible universe, it would not be the same thing we see during the day. See more at Wikipedia.org...

>This article is about the insect. For other meanings, see Fly (disambiguation) As defined by entomologists, a fly (plural flies) is any species of insect of the order Diptera, some of which can land on food and transmit bacteria to humans. A few, like Ormia ochracea, have very advanced hearing organs. Flies are common amongst humans and have caused many diseases to spread in the past. The house-fly (Musca domestica) and mosquito are particularly common amongst humans. Other flies, such as the horse-fly (Family Tabanidae), can inflict painful bites. The larva of a fly is commonly called a maggot. See more at Wikipedia.org...