ME reference ovals defined in this work, overlain on the pixelwise median-average aurora for each hemisphere. The new UVS reference oval is shown as a solid red line. The expanded and contracted HST ME reference ovals from Bonfond et al. (2012), shown as dashed yellow lines, and the northern reference oval from Nichols et al. (2017), shown as a magenta dotted line, are included for comparison. The pseudo-magnetic-coordinate reference point is denoted by a green cross, alongside the sense of pseudo-magnetic angle α. A 15°-by-15° grid in System-III longitude and planetocentric latitude is overlain on the aurora. The System-III longitude of certain gridlines are given in white, and the planetocentric latitudes of certain gridlines in magenta. The brightness scale of the images of the aurora in kR is given at the bottom of (b).