This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
It is due to scattering of light waves. 

(1)  Suppose you focus a torch light in your hand towards some distant object through air.   You will see some tiny particles moving rapidly in air.  We are able to see those particles because they scatter the light waves in all possible directions.  Those scattered waves fall on our eyes.

    If there is no scattering then we will not be able to see in the night, when all lights are switched off.   But we always can see faintly due to scattering. 

    When there is a laser beam in air during a laser show, we are able to see those due to scattering.  The light waves do not fall directly in our eyes. It is only scattered light we sense.

(2)  Every point on an electromagnetic wave (and light) acts as a source of the disturbance and can send the wave in all directions.  So the tiny particles in air or space act as sources of light and so we are able to see light even though the light beam of the original source is not directed towards our eyes.