In 1981, Robert Kirshner was working with other astronomers at the University of Michigan to calculate the redshifts –a measure of how fast something is moving away from Earth – of a great number of galaxies. Due to the way our Universe is expanding, the farther away a galaxy is the faster it moves, meaning redshift can be used to measure distance. Kirshner and his team were taking advantage of this to create a 3D map of the Universe. As the map became fleshed out, something strange appeared. At 700 million light-years from Earth was a blank void. In a roughly spherical region around 330 million light-years wide –a region the Milky Way could fit into billions of times over – there were barely any galaxies.