Day time sky colour blue.. night time sky colour black.. WHY?...?

light is scattered to make the sky blue at night there is no light

Sunlight, the sizes of the molecules that compose the atmosphere, refraction and reflection - Rayleigh and Mie scattering. That's why the sky can be blue or gray during the day and almost black at night. http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html

The nighttime sky is in fact NOT black. Is is a very dark midnight blue. The sky is a different color at night because at night the sun is on the other side of the earth. The earth is blocking sunlight from reaching the sky that you are seeing, and so it is dark. Think of a piece of paper with a flashlight behind it....and the the flashlight moves. (That's fairly inaccurate, but you understand what I'm saying, right?"

Day time is daytime because of the light from the sun - the earths atmosphere refracts the light from the sun - red is refracted most and is lost to the viewer and blue the least - we see only the blue. The night sky is black due to the absence of light.

Umm... could it be because our light source, little thing called `Sun`, is invisible at the time? You know, the Earth rotating on its axis, so 1/2 is illuminated, while other is in shadow?

Outer space is dark. Our atmosphere has certain elements in it that, when reacting with sunlight, cause the sky appear blue. No sun, no blue.