  The light curve of a distant Type Ia supernova acts like a clock that can be
used to test the expansion of the Universe. SN~1995K, at a spectroscopic
redshift of $z = 0.479$, provides one of the first meaningful data sets for
this test. We find that all aspects of SN~1995K resemble local supernova Ia
events when the light curve is dilated by $(1+z)$, as prescribed by
cosmological expansion. In a static, non-expanding universe SN~1995K would
represent a unique object with a spectrum identifying it as a regular Type Ia
supernova but a light curve shape and luminosity which do not follow the
well-established relations for local events. We conclude that SN~1995K provides
strong evidence for an interpretation of cosmological redshifts as due to
universal expansion. Theories in which photons dissipate their energy during
travel are excluded as are age-redshift dependencies.
