  We present observations of the galactic cepheids eta Aql and zeta Gem. Our
observations are able to resolve the diameter changes associated with
pulsation. This allows us to determine the distance to the Cepheids independent
of photometric observations. We determine a distance to eta Aql of 320 +/- 32
pc, and a distance to zeta Gem of 362 +/- 38 pc. These observations allow us to
calibrate surface brightness relations for use in extra-galactic distance
determination. They also provide a measurement of the mean diameter of these
Cepheids, which is useful in constructing structural models of this class of
star.
