Panagia, Gilmozzi, Macchetto, Adorf, and Kirshner determine the distance to SN 1987A via a purely geometric method: they compare the angular size of the circumstellar ring (measured with HST) to its absolute size (derived from the light-travel-time delay in the UV emission light curves measured by the IUE). They obtain a distance of 51.2 ± 3.1 kpc to the supernova and, by extension, to the Large Magellanic Cloud. This direct measurement, independent of standard candles, became a fundamental anchor point for calibrating the Cepheid distance scale and, by extension, the Hubble constant.