- noun the number linking the rate of recession of the galaxies with their distance from earth
- The number linking the rate of recession of the galaxies with their distance from us, now thought to be between 50 and 100km/sec of recession velocity per megaparsec of distance. The actual value of the constant has been the subject of strong disagreement, and Hubble himself thought that it must be far larger than the figure now accepted. There is also speculation among cosmologists that it may vary with time. Deep space analysis with the Hubble Space Telescope seemed in 1996 to support a figure of about 80km/sec per megaparsec, but this figure is still debated.