Scientists have known since the 1920s that the universe is expanding. Most of the earth's galactic neighbours are receding, and the farther away they are the higher is their velocity. Edwin P. Hubble who was known the a pioneer of modern astronomy analyzed the red shift of galaxies. He dicovered that the speed at which galaxy is receding is proportional to its relative distance. It means that more distant a galaxy, the faster it is moving away.
The principle was named Hubble's law. It can be represented as:
Speed=H× Distance
Where H is Hubble constant
A generally accepted value of H is 56 km per second per megaparsec( a megaparsec is 3.26 million light year).
