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Showing posts from September, 2017

### A Thirty-Year Search for just Two Numbers

Allan Sandage "the Father of Modern Astronomy" at the Carnegie Institution of Science, 2010

In 1926 the astronomer Victor Slipher measured the spectra of light from distant galaxies, in his soon-to-be, revolutionizing work he found that they were almost all shifted to longer wavelength by some amount, $\lambda$. What Slipher had in fact discovered would send tremors across the scientific community, what he noticed was the red shift of galaxies $\Delta \lambda /\lambda =v/c$ but he didn't appreciate yet, what this meant.

Eighteen years earlier, the Harvard astronomer Henrietta Swan Leavitt discovered a relationship between the period of Cephid variable stars and their luminosity which allowed astronomers (like Hubble) to calculate their distance from earth, provided one first knew what period of their evolution they were in.

Edwin Hubble was able to use the relation discovered by Leavitt to calculate the distances of various spiral nebulae (galaxies) which contained Cephi…