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WHY NIGHT SKY IS DARK? DAY SKY IS BLUE AND TWILIGHT SKY IS RED?

 

     Even in open ground, if you erect light bulbs in all the four corners, the ground will be flooded with light.  But universal space has lots and lots of stars (actually suns).  Then, why the night sky is pitch dark?

      To answer this question, we have to go billions of years back.  That is the birth time of the universe.  Long, long back, the matter for the entire universe was contained in a tiny atom.  The tiny dot has zero size, large mass, infinite density.  There was 'big bang', an astronomical explosion.  The entire matter was thrown out.  The universe was born.  The time started to tick.  Explosion temperature begins to cool down.  Galaxies, star systems formed.  They all continue to move and expand like a balloon[due to explosion].  Even today, all celestial bodies continue to move away from us.  The expansion of the universe is the greatest discovery of the century.

      Next, we have to understand 'Doppler effect'.  When a train approaches us, the frequency of whistle sound increases and when it recedes, the frequency decreases.  This is called the Doppler shift. 
      It is applicable to light also.  When a star moves away from us, the frequency of light shifts to the infrared side.  That is, visible light becomes invisible infrared rays.  That is why we loose light from distant stars and space is always dark.

     Why the day-sky is blue?  The air molecules scatter the blue colour (in the sunlight) more than other colours.  It gives the illusion of blue sky.  During sunset and sunrise, the light rays have to travel a long distance in the atmosphere.  Hence all the colours are scattered away.  Mostly red light reaches our eyes.  Hence we see blood-red sunset.

     So the sky is a misnomer.  It is an interplay of colours and just illusion.
     Let poets, painters, photographers enjoy the drama in sky theatre.  Let us join them too.   



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