Why the space is cold?

     Before we knowing the reason why the space is cold?  We should know, is it cold?  Yes, we get cold in space.  For example, you can see in Iron man 2 (Iron man mark 2 test fight), the more he fly higher, the more he get cold and freeze.

     Some questions may rise in our mind.  More than billions of stars are present in the space, why the space is not hot?  

       Just think of our solar system.  The heat from the sun is more for nearest planets while comparing to the farthest planets. So, heat get reduce when the distance get more.  

       From the Earth, we can see the stars are close to each other.  Actually it isn't.  The distance between the one star from another is some billion light years. A Light year is nothing but the distance traveled by the light in one year(9,460,730,437,000,000 metres).  Then think of that, how much distance the stars will be. Now we can understand that the space is vacuum, so the space won't get hot by the stars. 

     Actually the space is not cold.  There is no temperature in the space.  Then how comes cold?

     Before that, we should know about the heat transfer.  There are three types of heat transfer, they are

     1. Conduction  (transfer via solid materials)

     2. Convection  (liquid and gas)

     3. Radiation    (electromagnetic radiation or waves)

Focus on radiation.  For example, the Sun(it radiates energy).

     Let us make more simple.  Consider, you are a rich man.  You spending your property continuously without gaining anything.  What will happen?  You will get into poverty state.  Even though you spending continuously, without gaining.  Now, what will happen?  You will still attain more poverty.

     Now come to the question.  You are in the space.  Your body start to loss heat by radiation and there is no more heat gain in the space.  So, you automatically get cold and freeze in the space.  Actually the space is not cold, we getting cold due to heat transfer.