We report on measurements of the cosmic-ray induced \gamma -ray emission of Earth ’ s atmosphere by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope .
The LAT has observed the Earth during its commissioning phase and with a dedicated Earth-limb following observation in September 2008 .
These measurements yielded \sim 6.4 \times 10 ^ { 6 } photons with energies > 100 MeV and \sim 250 hours total livetime for the highest quality data selection .
This allows the study of the spatial and spectral distributions of these photons with unprecedented detail .
The spectrum of the emission – often referred to as Earth albedo gamma-ray emission – has a power-law shape up to 500 GeV with spectral index \Gamma = 2.79 \pm 0.06 .