Hubble Constant H0
is needed to estimate the size and age of the Universe.
v = H0d
v = recessional velocity of a galaxy
from spectroscopic observations of the galaxy's redshift, indicating its radial velocity. The recessional velocity, v, is related to the galaxy's redshift, z, via the formula v = c z, where c is the speed of light, 3 × 105 km/s.)
d =the galaxy's precise distance from earth
The units of the Hubble Constant are kilometers per second per megaparsec.
Source: "Lifting the Veil on Hubble's Constant"http://science.nasa.gov/newhome/headlines/ast25may99_2.htm May 25, 1999 Author: John Horack [Date accessed 5 Jun 2000]
The Hubble Constant describes how fast objects appear to be moving away from our galaxy as a function of distance. If you plot apparent recessional velocity against distance, as in the figure left, the Hubble Constant is simply the slope of a straight line through the data.
Estimates vary of H0 from =55+/-6 km s-1 Mpc-1 to 70 km s-1 Mpc-1. http://www.hubbleconstant.comAn estimate of H is =71+/-6 km s-1 Mpc-1.