1978: Vera Rubin and Kent Ford Discover Dark Matter

Vera Rubin. Image courtesy of the Observatories of the Carnegie Institution for Science.

Sometimes discoveries happen when scientists set out to measure something routine and are completely surprised by the result.  Such was the case when astronomers Vera Rubin and Kent Ford at the Carnegie Institution's Department of Terrestrial Magnetism, began a series of observations to measure the mass of spiral galaxies.  As they collected and analyzed data from several galaxies, they were astonished to find that the mass of a galaxy was much greater than would be expected based on the visible mass of bright stars and glowing gases.  In some cases the mass of a galaxy was found to be ten times greater than expected.  The obvious conclusion, since confirmed by many other astronomers, was that the galaxies contained “dark matter” that could not be seen.  Discovering the nature of this dark matter continues to be a major area of investigation in astronomy today.