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Do You Know
Questions & Answers on General Knowledge.
Why isn't the sky bright blue when the sun is red?
During the day, the sky is blue because the air and dust in the air scatter mainly blue light toward your eyes. They also scatter some red light, but the blue light dominates. But at sunset, things change. The setting sun approaches the earth's atmosphere at a very shallow angle so that it must travel many kilometers through the air before reaching your eyes. During this long trip, most of the blue light is scattered away and the sun appears very red. If the path is long enough, the blue light is scattered away many kilometers to your west so that there isn't much of it left. When this occurs, even the sky around you appears somewhat reddish because there just isn't any more blue to scatter. The missing blue light is visible to people living 50 or 100 kilometers to the west as their blue sky.
Knocking on wood or simply saying knock on wood after making a hopeful statement finds its roots in the idea that youre tempting fate by acknowledging your good fortune. Its believed that the expression comes from an ancient belief that good spirits lived in trees so by knocking on something wooden a person was calling on the spirits for protection. Another reason why we should all be tree hugers.