Simultaneous observaions of auroral emissions and particle precipitation in the 19--24 MLT sector by instruments on the Isis 2 satellite are reported. The optical intensity of the diffuse aurora is found to be produced mainly by a relatively uniform precipitation of low-energy electrons between about 100 eV and 10 KeV aith monotonic energy spectra. Discrete auroras are embedded within but usually in the poleward portion of the diffuse aurora and are caused by highly structured and intense electron precipitation. The corresponding electron energy spectrum consists of a monotonic component similar to that in the diffuse aurora and a peaked component often narrower than a Maxwellian spectrum. Several characteristics of the precipitaion associated with the diffuse aurora support the identification of the diffuse aurora as the optical image of the earthward termination of the plasma sheet at the auroral altitudes. This suggests that the source particles of discrete auroras lie along the geomagnetic field lines within but usually near the poleward boundary of the plasma sheet. The background boundary for energetic electrons (E>40 keV) is frequently observed to extend up to the location of discrete auroras, some cases of clearly discernible pancake type pitch angle anisotropies suggesting that some of the discrete auroras are on closed field lines. Protons precipitate in both the discrete and the diffuse auroral region but do not contribute significantly to the total energy flux, except near the equatorward boundary of the diffuse aurora, where the proton flux can be dominant in some cases.