We tend to think of the Sun as an image of its disk. Recent years have broughtincreasingly sophisticated images of that disk in the light of single spectral lines andimages of active emissions from its surface and its corona with higher and higherspatial resolution. However, we have no such images of solar energetic particles(SEPs). In a photon-dominated discipline, SEPs are stealthy and obscure; they areinvisible in the solar sky. While photons travel line-of-sight, SEPs are guided out tous along open magneticfield lines. We must measure, identify, and count SEPsdirectly one by one. Only in recent years have we overcome the limitations so ourobservations now begin to bear richer fruit. This is the story of that development.Solar energetic particles (SEPs) come as bursts of high-energy particles from thedirection of the Sun lasting for hours or sometimes days. The particle energies rangefrom about 10 keV (kilo electron volts) to relativistic energies of several GeV,particle speeds 90% of the speed of light. In addition to the dominant protons andelectrons, all of the other chemical elements from He through Au and Pb have nowbeen measured. The relative abundances of these elements and their isotopes havebeen a powerful new resource in our quest for understanding the physical processesof acceleration and interplanetary transport of SEPs which alter those abundances indistinctive ways.