Hubble's Law

Hubblesinglequotes Law:

Hubblesinglequotes Law founded by American astronomer Edwin Powell Hubble in 1929. This discovery by Hubble changed the understanding of the universe by the mankind forever. His law proved that there are other galaxies beyond milky way and the universe is expanding.
 Hubblesinglequotes law states that the universe is expanding and the galaxies are receding away from each other. And the speed of recession of any galaxy from us is directly proportional to itsinglequotes distance from us.
    This phenomenon was observed by as a redshift of the galaxysinglequotes spectrum.The redshift indicated that the galaxies are receding away from each other and this redshift had a large value of displacement for faint (hence more distant) galaxies, which meant that the galaxies farther from earth are also receding at a greater speed.( This moving away of galaxies is leading to the expansion of the universe).Mathematically it is given by:

v = H₀d
        where v = velocity of the receding galaxy radially outwards.
                        H₀ = Hubblesinglequotes constant
                         d = distance of the galaxy from earth.

 H0 is denoted with a subscript singlequote0singlequote which means the current value of Hubblesinglequotes constant. (Funny, isnsinglequotet it?) Hubblesinglequotes constant is called a constant though its value changes with time and we always use the current value of the Hubblesinglequotes constant in the equation above. Hubblesinglequotes constant is one of the very important parameters in astronomy (cosmology, to be specific) as it helps in finding the age of the universe.

The SI unit of Hubblesinglequotes constant is second-1 but the one more commonly used is (Km/s)/Mpc which gives the speed of the galaxy in Km/s one Megapersec away. (Note that Megapersec is a unit of distance).So we say that the unit of Hubblesinglequotes constant is "kilometres per second per megapersec".Therefore a value of 100 Km/s/Mps would imply that a galaxy will have a redshift corresponding to a velocity of 1000 Km/s if it is 10 Mpc away.
 The reciprocal of H0 is called Hubble time.

So, the graph between recessional velocity and distance gives a straight line.A majority of galaxies follow this behaviour and are said to follow the course of smooth expansion.Hubblesinglequotes law is also sometimes called Hubblesinglequotes expansion law.

The graph between recession speed and distance is as follows:

Some points fall exactly on the line.They are said to follow the smooth expansion curve while others show slight deviations owing to certain other motions.Each point represents a particular galaxy.