Hubble's Law of Red Shift and Expansion of Universe

The Hubble's Law is the only accepted principle of measuring the distance of far away galaxies. It uses the known rate of Red Shift change and telescopic observation to calculate the distance and recession speed of galaxies from us. The diagram on the left is the recession velocity in km/sec of extragalactic nebulae plotted against their distances in parsecs as originally observed by Edwin Hubble in 1929.   

The recent observations is as follows:-

The left diagram is a more recent velocity-distance diagram showing the expansion of the universe. The lower-left corner is the region of universe originally surveyed by Hubble in 1929 using much lower power telescopes. The recent graph clearly shows that the recession velocity (vertical scale in thousands of km/sec) is directly proportional to the distance (horizontal scale in billions of light years) of observed Constellations.  

In this graph, a = Virgo, b = Perseus, c = Ursa Major, d = Corona Borealis, e = Boötes, and f = Hydra.

The Hubble Sphere is the graphic theme of the expansion of universe.

The left figure is symbolic graph of the expansion of universe called Hubble Sphere. In this graph, the circle represents the Observable Universe; Where 

"A" =  the recession speed of galaxies is less than the speed of light (in vacuum).

"C" = the speed of recession is equal to the speed of light, and 

"B" = the recession speed of galaxies is faster that the speed of light.  

When the speed of galactic recession becomes faster than the speed of light, it also becomes impossible to observe what goes on beyond the limit of this Hubble Sphere, as no signal or information can reach us. Thus the term the "Observable Universe".

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