The value of the Hubble constant, H 0, tells the rate at which the universe is expanding. In 1929, Edwin Hubble determined for the first time this constant to be 500 km/s per million parsecs. Since then, Hubble constant has been actively measured using various methods. In the early days, Hubble, for example, used bright stars and the light of the "nebula" to estimate the redshift and determined the constant. Later, after type Ia supernova was found to be a better " standard candle " of distant galaxies, supernova were used to determine the redshift. These measurements need to determine the distance of the target stars or galaxies first. Uncertainties in the physical assumptions used to determine these distances have caused varying estimates of the Hubble constant.