An examination of the equatorial boundary of the auroral oval (as defined by quiet-time auroral electron precipitations) reveals a periodic variation of its latitudinal location. The period of oscillation is 24-hours and the amplitude is about 4¿. This diurnal variation seen in the evening and morning sectors of the auroral oval is in phase as is the diurnal variation of the northern and southern hemispheres. The observed latitudinal variation is attributed to UT diurnal variation of the auroral oval size in association with the daily precession of the geomagnetic pole. The auroral oval is smaller when the northern geomagnetic pole is near the local midnight around 0600 UT; it is larger when the northern geomagnetic pole is near the local noon around 1800 UT. The equatorial edges of the eveing sector of the quiet auroral oval (1900--2100 MLT) are located at about 72¿ and 69¿ CGl, respectively, which correspond to the minimum auroral oval.