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Why the Sky and Ocean is Blue when Universe is Dark?

By Edited May 18, 2016 1 0

Is Anything Actually Colored?

Credit: from pixabay

Why Do Black Colored Materials Get Readily Hot


        White Colored Materials Remain Cool

The color of a material or substance is not its property but is actually what we observe.

Let me explain,

To be more precise the color we observe in material is actually only reflecting that particular color for e.g. when white light consisting of all colors falls on grass then all its colors are absorbed by the grass except green so it reflects green color and we say that grass is green.

Same goes with the rest of the materials. Anything you see blue or red are just the reflections of that material not the actual thing. Now you know why Black colored things get readily hot, because they absorb all of the white light without reflecting any of it and in this way it stores a lot amount of heat. This is the exact opposite of white colored materials which reflects the light completely and stays cool for prolong periods as no heat rays are stored. Which is also the reason the houses are painted white.

Why is Ocean Blue
Credit: Wikipedia commons

 Why Is The Ocean Blue When Water Is Transparent

Science teacher: "Can Anyone tell me the names of the largest and smallest bone in our body and their location?" 

Jack :"The spinal cord is the Largest bone and the bone in my little finger is the smallest."

Science teacher: "Wrong, Anyone else...David you've got the highest grades in my subject why don't you tell me."

David: ''Well, the largest bone is the Femur which is the thigh bone about 1 meter long in average person. The Smallest is the Stirrup located in the ear, it is about 3 millimeters long.''

Science teacher: ''Correct!''

Science teacher: "OK, here's a hard one why the ocean is Blue when we know that the water is transparent."

Jack: After some hard thinking, "You see the water reflects things for example I can see my face in it so it is safe to assume that Ocean reflects sky which is Blue and directly above it so the ocean appears Blue."

Science teacher: "A clever deduction but you're wrong again Jack."

Science teacher: "Anyone else looking towards David."

David: sighs "The behavior of light rays or electromagnetic rays depend on the composition of matter they passes through so when light enters the ocean water then all the light colors of larger wavelengths are absorbed while the lights of shorter wavelengths are reflected as Blue color radiation has about the shortest wavelength so it is reflected and thus we see blue color."

Science teacher: "Correct again, excellent David."




Why Is Sky Blue

Credit: from pixabay

       Why Is Sky Blue While Universe is Dark

Now lets first distribute it into two parts, lets address the former first.

Why Is Sky Blue

As mentioned earlier the behavior of these electromagnetic waves are determined by the

Rayleigh scattering
composition of matter they passes through and as the earth's atmosphere we know that the earth's atmosphere deflects the lights of shorter wavelengths more than longer ones. ( See below the prism deflects the blue lights most and the red light least). Because of this the red light passes through while the blue light scatters all around and we can see it almost everywhere in the sky. This phenomena is known as Rayleigh scattering 


Light being scattered by prism

Its worth mentioning that as the light covers more distance reaching the horizon so the sky looks much paler there, as more of the blue light is scattered and reached our eyes.   

Why Is The Universe So Dark

Credit: from pixabay

Why Is The Universe Dark

It is understandable to say that since the the universe contains billions of stars like the sun even  more larger ones then why in the world is the universe Dark ? If the universe is infinitely old then the light should have lighten the galaxy ?

 This is known as Olbers' paradox.

Olbers' paradox


The answer is simple even though the numbers of stars is so vast the space still is humongous its like searching for a pebble in a huge pool. The Truth is the universe is about 13.7 billion years old and only the light of stars 13 billion light years ( distance traveled by light in one year  which is 3.461 e+12 Km) away can reach us further more the stars are moving away from us the phenomena is called red shifting (more on that some time later) which is similar to Doppler's effect. Another factor that contributes to this is the density of space.

Doppler's effect


Dooppler's effect

According to Chaisson, Eric, & Steve McMillan.Astronomy Today. New York: Prentice Hall, 1993: 418.

"It averages roughly 1 atom per cubic centimeter, but density as great as 1000 atoms/cm3 and as small as 0.1 atom/cm3 have been found."


According to Mitten, Simon & Jacqueline. The Young Oxford Book of Astronomy.1995: 94.

"If you went out in space to a spiral arm of the galaxy, you would find one to two atoms of gas per cubic inch!"



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