Illustration: NASA/Sonoma State University/Aurore Simonnet
The Fermi Gamma-Ray Space telescope (formerly known as GLAST). The Large Area Telescope measures high-energy photons via detection of electron-positron pairs produced in tungsten sheets inside the direction-sensitive tracker towers. The energy of the pairs is measured in the calorimeter unit under the tracker. In this work the telescope is used to measure primary electrons and positrons.