Almost all primary cosmic rays are charged particles—mostly protons. But the one primary in a thousand that's a gamma has special value for astrophysicists. The arrival direction of a charged particle of energy less than1018 eVreveals nothing about where it came from. That's because the random microgauss magnetic field pervading the galaxy thoroughly scrambles the trajectories of all but the most ultrahigh‐energy charged particles (which are presumed to originate somewhere beyond the galaxy). But gammas, being impervious to magnetic fields, are superb astrophysical pointers.