Though not currently engaged in research, while in graduate school at Vanderbilt University I was a member of the Supernova Cosmology Project. The SCP is a multinational collaboration involved in determining the value of cosmological parameters through the observation of distant Type Ia supernovae. In the late 1990s, the SCP was the first to discover evidence for the cosmological constant, the dark energy responsible for the acceleration of the expansion of the universe, the discovery of which won Dr. Saul Perlmutter (the leader of the SCP) the Nobel Prize in Physics in 2011. My own specialty in the group was the identification of Type Ia supernovae through spectral analysis.
The current webpage for the Supernova Cosmology Project can be found here.