During the period November 10–22, 1967, the earth‐moon system was bathed in an isotropic, homogeneous beam of solar electrons and protons whose intensities were slowly varying functions of time. Detailed angular distribution and intensity observations of these particles and vector magnetometer observations made simultaneously by the lunar orbiting satellite Explorer 35 are combined to examine particle shadowing effects by the moon. During the observing period, the moon and Explorer 35 passed from interplanetary space through the magnetotail. Simultaneous observations were made by the earth orbiting satellite Explorer 33, which was sunward of the earth's shock front and at large radial distance from the earth during most of the observing period. The angular distributions of the intensity of both electrons and protons were accurately isotropic within the magnetotail as well as in interplanetary space. Study of 33 cases of clearelectronshadowing and two cases of less clear shadowing suggests the following principal conclusions: (a) Magnetic lines of force from external sources thread through the moon in a rectilinear manner as though it did not exist. The accuracy of this statement is measured by the maximum departure from rectilinear projection that is permitted by the electron shadowing observations. This is approximately 0.1RM(lunar radius) in 2RMor 3°. (b) Electron shadowing data provide nodirectinformation on the region of access of interplanetary electrons into the magnetotail but do provide an upper limit on the trans‐B diffusion velocity υ⊥of electrons due to all causes. In the central portion of the magnetotail during magnetically quiet conditions and for radial distances ≲ 64 RE(earth radius), υ⊥≲ 100 km sec−1for 50 kev electrons. This upper limit requires, among other possibilities, that the transverse electric field Lunar shadowing of protons (Ep≳ 322 kev) is also described and discussed but is of mu