The Black Sky & White Sun

  Doesn’t this title seem pretty strange with slight twist..? I'm sure that you would have repeated at least twice this title, same happened with me when I glance over this statement in an article recently. Dark sky-white sun! But you & I have seen normally is yellow sun on earth. I just couldn’t control my curiosity and started pitching my Guruji for the same (I haven’t made a move with such questions in my school days to be frank;  referring Guruji to Google here) and finally understood that…

    Out in space, the sky looks dark and black, instead of blue. This is because there is no atmosphere. There is no scattered light to reach your eyes. 

Why is sky blue on earth?

    Light from the sun or a light bulb may appear as white, but it is actually a combination of 7 colors.Way back to school days, we all have experienced the same with piece of glass- PRISM.

Light travels through space in a straight line as long as nothing disturbs it. As light moves through the atmosphere, it continues to go straight until it bumps into a bit of dust or a gas molecule. Then what happens to the light depends on its wave length and the size of the thing it hits.

     Dust particles and water droplets are much larger than the wavelength of visible light. So while hitting these large particles, it gets bounced off in different directions. The reflected light appears white because it still contains all of the same colors. 

     As gas molecules are smaller than the wavelength of visible light, some of it may get absorbed & radiates (gives off) the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. Though all of the colors can be absorbed, but the higher frequencies (blues) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering (It is named after Lord John Rayleigh, an English physicist, who first described it in the 1870's.) When absorbed high frequencies (blues) radiated in different directions, it gets scattered all around the sky. And hence whichever direction you see, the sky looks blue!

Why sunset RED?

      As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes.