What is "Hubble's Constant"?

Hamlet.

Hubble's law is the statement in astronomy that galaxies move away from each other, and that the velocity with which they recede is proportional to their distance. It leads to the picture of an expanding universe and, by extrapolating back in time, to the Big Bang theory. The law was first formulated by Edwin Hubble in 1929. Hubble compared the distances to nearby galaxies to their redshift, found a linear relationship, and interpreted the redshift as caused by the receding velocity. His estimate of the proportionality constant, now known as Hubble's constant, was however off by a factor of about 10. Furthermore, if one takes Hubble's original observations and then use the most accurate distances and velocities currently known, one ends up with a random scatter plot with no discernable relationship between redshift and velocity. Nevertheless the relationship was confirmed by observations after Hubble. The law can be stated as follows: v = H0 D where v is the receding velocity of a galaxy due to the expansion of the universe (typically measured in km/sec), H0 is Hubble's constant, and D is the current distance to the galaxy (measured in mega parsec Mpc). http://www.nationmaster.com/encyclopedia/Hubbles-law This time I didn't use my Physics Answer book... Feb 04 04, 6:36 PM