Why Is the Sky Blue?
The vast regions of outer space are shrouded in darkness. What we call sky is the atmosphere that surrounds the earth, the region of space that is visible to the human eye. Looking up into this large expanse, the sky, many have wondered, ‘Why is the sky blue?’ Why not violet, green, yellow, orange, or red—the other basic colors of the visible spectrum?
Sunlight consists of light of various wavelengths, which are seen as the different colors of the visible spectrum. The longest of these light waves are red, and the shortest are blue or violet. The gas molecules of our atmosphere scatter far more light of the shorter wavelengths, the blue, than of the longer wavelengths, the red. As a result, clear sky has a blue color. The air surrounding the earth, with its innumerable particles of solid materials, such as dust, scatters light to give the appearance of visibility, as though reflected from a mirror.
On the other hand, when the sun is near the horizon, sunlight travels through a greater amount of atmosphere to reach the eye, and the longer waves penetrate better than the shorter waves, causing the sky to take on a deep orange and red appearance. Solid particles in the air accentuate the reddening. Similarly, when smoke or dense clouds fill the sky, light waves of all colors are scattered. This causes the sky to appear gray.
This awesome display of God’s use of light in the atmospheric heavens reminds us of the words of the psalmist: “The heavens are declaring the glory of God; and of the work of his hands the expanse is telling.”—Psalm 19:1.