The spatial distribution of auroral emissions on a global scale. This falsecolor image of the northern auroral oval at vacuum-ultraviolet wavelengths is overlaid with a coastline map to show how the nearly instantaneous auroral oval maps onto the polar regions. The noncircular distribution of luminosities arises in large part from the non-dipolar components of the magnetic field, and is observed to rotate diurnally. Indeed, a trained observer can estimate Universal Time by studying the instantaneous spatial distribution of auroral emissions. The noncircular nature of this distribution is less prominent in the southern polar region. In magnetic coordinates these spatial distributions are nearly circular in both hemispheres. This image was obtained with The University of Iowa's auroral imaging instrumentation during the 12minute period beginning at 0229 UT on 8 November 1981, about seventy minutes after the arrival at Earth of a shock in the interplanetary medium. The sensitivity passband of the ultraviolet wavelength photometer for this image extends from 123 to 155 nm. Auroral emissions at these wavelengths arise predominantly from the emission lines of atomic oxygen at about 130.4 and 135.6 nm and from the Lyman-Birge-Hopfield bands of molecular nitrogen. These emissions rival in intensities the emissions from the sunlit hemisphere at large solar zenith angles as seen here in the upper left portion of the image. The auroral oval approaches the terminator at local noon.