  Phase closure at 682 GHz and 691 GHz was first achieved using three antennas
of the Submillimeter Array (SMA) interferometer located on Mauna Kea, Hawaii.
Initially, phase closure was demonstrated at 682.5 GHz on Sept. 19, 2002 using
an artificial ground-based "beacon" signal. Subsequently, astronomical
detections of both Saturn and Uranus were made at the frequency of the CO(6-5)
transition (691.473 GHz) on all three baselines on Sept. 22, 2002. While the
larger planets such as Saturn are heavily resolved even on these short
baselines (25.2m, 25.2m and 16.4m), phase closure was achieved on Uranus and
Callisto. This was the first successful experiment to obtain phase closure in
this frequency band. The CO(6-5) line was also detected towards Orion BN/KL and
other Galactic sources, as was the vibrationally-excited 658 GHz water maser
line toward evolved stars. We present these historic detections, as well as the
first arcsecond-scale images obtained in this frequency band.
