South Pole Telescope detector. Full South Pole Telescope (SPT) detector at the Silicon Detector Facility (SiDet) at Fermi National Accelerator Laboratory (Fermilab), Illinois, USA. One of the goals of the SPT is to determine the masses of the universe's neutrinos. Though nearly massless, they contribute to the total mass of the universe and affect its expansion. By mapping out the mass density of the universe through measurements of Cosmic Microwave Background (CMB) lensing, astrophysicists are trying to determine the masses of these elusive particles. Photographed on 22 May 2015.