What initial value for the proportionality factor did Hubble publish in his 1929 compilation of distance and velocity data?

Answer

$500 ext{ km/s/Mpc}$

When Edwin Hubble compiled distance estimates for numerous galaxies along with the corresponding radial velocity measurements obtained by Vesto Slipher in 1929, he calculated a proportionality constant, $H_0$, based on the data available at that time. This initial measurement resulted in a value of $500 ext{ km/s/Mpc}$. It is important to recognize that this figure was significantly larger than contemporary values, which are estimated to be around $67-74 ext{ km/s/Mpc}$. The discrepancy stems from calibration errors inherent in the early use of Cepheid variables as standard candles. Despite the numerical inaccuracy, the fundamental principle derived—that velocity scales linearly with distance—was revolutionary and sound.

What initial value for the proportionality factor did Hubble publish in his 1929 compilation of distance and velocity data?

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