Answer to Question #51739 in Optics for sahil raza khan

Question

Explain in brief why color of sky and sea or ocean appears to be blue.

Answer 1

Both the sky and the ocean are blue, but for two very different reasons.

The sky is blue because of something called Rayleigh scattering. For very small particles such as individual molecules, the wavelength of light that is reflected is a function of the particle size and type of molecular bonds between atoms. The atmosphere tends to scatter shorter wavelength (blue) light to a greater extent than longer wavelength (red) light. Blue light from the sun is scattered every which way, much more so than the other colors, so when you look up at the daytime sky you see blue no matter where you look.

The ocean is not blue because of scattering. Instead, the ocean is blue (as is pure water) because of selective absorption. Liquid water absorbs preferentially both short wavelength light (UV) and longer wavelength visible and infrared light. Of the visible light, the longest visible wavelengths are absorbed most (red-orange, 600-700nm), then the medium-length visible wavelengths (yellow-green, 500-600nm) and last the short visible wavelengths (blue-violet, 400-500nm). The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets. This is the main reason why ocean color is blue.