Why is the Sky Blue?

The sky is blue because the ocean is blue. The sky reflects the color of the ocean.

The sky is reflective just like your windows at night. You can try this at home. Tonight, if it gets dark where you are, turn on all the lights in a room and try to look out the window. All you can see is your own reflection (unless you are a vampire, they you will just see the reflection of the room). This is because the reflected fraction of the light from inside the room prevents you from discerning the light from outside.

During daylight hours the sun lights up the earth (think the room in your house) brighter than space, and so all we see when we look at the sky is the reflection of the oceans, which cover 2/3 of the surface of the earth. At night, when the sun is not shining earth becomes dark, space appears brighter, we get no reflection off the sky, and we can see right through the sky and see the stars.

An interesting thing happens on overcast days. The sun can not shine on the earth bright enough to get full reflection, as a result we are able to see some of the blackness of space, leaving a blueish-gray appearance to the sky.