Slipher's work on spectra enabled this quantity's first measurement, which was very large since clusters were assumed to be (*) bright stars.
This quantity names a void that attempts to solve the SandageÂ–de Vaucouleurs paradox. Baryon acoustic oscillations constrain this quantity, which is the first rung of the inverse distance ladder. Sandage wrote about a search for two numbers: the deceleration parameter and this one. Slipher's work on spectra enabled this quantity's first measurement, which was very large since clusters were assumed to be (*) bright stars. This quantity was the slope of a line through the origin on a plot of 24 "nebulae" whose values were obtained from Cepheid variables. This parameter is defined as aÂ­dot over a, where a is the scale factor. Its reciprocal is an estimate of the Universe's age, and its current value is around 67 km per second per megaparsec. This constant relates distance to redshift, or velocity, in a "law" for galaxies far, far away. For 10 points, identify this "constant" that describes the Universe's expansion and is named for an American astronomer.
This quantity names a void that attempts to solve the SandageÂ–de Vaucouleurs paradox.
Hubble constant [or Hubble parameter; accept Hubble bubble; prompt on "the rate the Universe's expansion" or equivalents until read]