Lawrence Berkeley National Lab's Saul Perlmutter with a view of the supernova 1987a in the background. The Supernova Cosmology Project, based at Berkeley Lab and headed by Saul Perlmutter of the Physics Division, shares the citation with the High-Z Supernova Search Team led by Brian Schmidt of Australia's Mount Stromlo and Siding Spring Observatories. Both teams are international collaborations, with researchers in England, France, Germany, and Sweden among the members of the Supernova Cosmology Project. Thus how bright they appear reveals their distance. By comparing the distance of these exploding stars with the redshifts of their home galaxies, researchers can calculate how fast the Universe was expanding at different times in its history.
Good results depend upon observing many type Ia supernovae, both near and far.
Before the Supernova Cosmology Project employed search techniques developed during the first five years of its existence, finding supernovae was a haphazard proposition, which made it difficult to secure telescope time to observe them. To get telescope time, you had to guarantee you were going to find a supernova. Each contains roughly a thousand distant galaxies. Three weeks later the same patches are imaged again. In these three weeks, the supernovae typically have not yet reached their brightest moments.