Distance to the Cygnus Loop from Hubble Space Telescope imaging of the primary shock front

We present a Hubble Space Telescope (HST) Wide Field Planetary Camera 2 nar rowband Ha image of a region on the northeastern limb of the Cygnus Loop su pernova remnant. This location provides a detailed example of where the pri mary blast wave first encounters the surrounding interstellar medium. The f ilament structure is seen in exquisite detail in this image, which was obta ined primarily as an EARLY ACQuisition image for a follow-up spectroscopic program. We compare the HST image with a digitized version of the POSS-I re d plate to measure the proper motion of this filament. By combining this va lue for the proper motion with previous measurements of the shock velocity at this position we find that the distance to the Cygnus Loop is 440(-100)( +130) pc, considerably smaller than the canonical value of 770 pc. We brief ly discuss the ramifications of this new distance estimate for our understa nding of this prototypical supernova remnant.