sky wiki:
>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...
night wiki:
>This article describes the time of day. For the work by Elie Wiesel, see Night (book). For the Norse goddess see Nótt. Night is the time when a location is facing away from the Sun, and thus dark. On Earth, it is night on just under half the planet at any time. When it is night on one side of the planet, it is day on the other side. Because of the rotation of Earth about its axis, it is alternately day and night, which together form a 24-hour day. The Earth's tilt also means that the nights are shorter in the seasons of summer and longer in winter.
See more at Wikipedia.org...