is needed to estimate the size and age of the Universe.

v = H_{0}d

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 × 10^{5} 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 |
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 H |

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