The Explorer 33 satellite was launched July 1, 1966 and was injected into a highly elliptical earth orbit. The Goddard Space Flight Center magnetic field experiment onboard the spacecraft consists of a triaxial fluxgate sensor with a maximum dynamic range of ±64 gammas and a sensitivity of ±0.25 gammas along each axis. Because of the initial apogee-earth-sun angle of 118° west of the sun, the first 8 orbits of Explorer 33 (July-November 11, 1966) mapped the earth's magnetosheath and magnetic tail from the western flank of the bow shock to the eastern flank. This mapping of the geomagnetic tail out to 80 earth radii established that the tail extends beyond the lunar orbital distance. Explorer 33 has also found that the earth's bow shock is still a detectable boundary between the interplanetary magnetic field and the downstream magnetosheath at a geocentric distance of 75.7 earth radii. This spacecraft has further revealed that the cross-section of the geomagnetic tail is probably not cylindrical, and that the magnetic field magnitude in the tail decreases with distance down the tail from the earth. This magnitude decrease can be due both to a gradual expansion of the tail with distance and to a reconnection of magnetic field lines across the tail neutral sheet. / M.S.