A highly magnified supernova at z=1.703 behind the massive galaxy
  cluster Abell 1689
  Our ability to study the most remote supernova explosions, crucial for the
understanding of the evolution of the high-redshift universe and its expansion
rate, is limited by the light collection capabilities of telescopes. However,
nature offers unique opportunities to look beyond the range within reach of our
unaided instruments thanks to the light-focusing power of massive galaxy
clusters. Here we report on the discovery of one of the most distant supernovae
ever found, at redshift, z=1.703. Due to a lensing magnification factor of
4.3\pm0.3, we are able to measure a lightcurve of the supernova, as well as
spectroscopic features of the host galaxy with a precision comparable to what
will otherwise only be possible with future generation telescopes.
