Why sky and ocean appear blue while clouds appear white or gray? On a clear day whenever we look upwards we see the clear blue sky and sometimes white clouds as well. From the beach when we look at the ocean the ocean also appears blue. Let’s analyze why sky and ocean appear blue and clouds appear white or gray.

To understand the color of sky, ocean, or clouds we have to understand the light itself. The visible light coming from the sun is not actually white. It consists of all the rainbow colors ranging from red to violet. When this light with complete color spectrum hits the atmosphere of the earth the air molecules scatter blue part of the light spectrum more than the red part of the spectrum. Therefore when this blue scattered light reaches our eyes it gives the sky blue appearance. The appearance of clear blue sky depends on the atmosphere clarity. If the atmosphere is clear, not dusty then only air molecules consisting of oxygen and nitrogen atoms scatter blue light. If the atmosphere contains more dust particles then sky does not appear clear blue. Instead it appears hazy or foggy.

Why does sky appear orange or reddish at sunrise and sunset? This is also due to the scattering of light. At sunrise and sunset light has to travel longer distance which does not allow the short wavelength blue part of the light spectrum to reach our eyes as it has been already scattered out, outside our line of vision. Instead the red part of the spectrum with longer wavelength hit our eyes which gives the sky orange or reddish appearance at sunrise and sunset.

Why are clouds white or gray? Clouds contain water molecules which are bigger than the air molecules. These molecules do not scatter any part of light’s color spectrum more, instead they scatter all of color spectrum equally, therefore when light coming from these clouds hit our eyes it consist of full color spectrum. The complete color spectrum of light is white, therefore the clouds appear white. If the clouds become thick enough or high enough and the light cannot penetrate or make it through the cloud then they appear gray. The thick clouds have more water molecules in them which scatter light even more. This doesn’t allow the light to penetrate which can give dark gray appearance.

Ocean appears blue because water absorbs longer wavelengths of light which is red part of the light spectrum. The water molecules absorb infrared, red and ultraviolet light first, and then yellow, green and violet. This leaves only blue light to reach our eyes. This is how ocean appears blue from the beach.

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