A submm heterodyne receiver has been used for radiometric measurements of the sun, moon and Jupiter and for the detection of the CO J = 6 -> 5 rotational transition at 691 GHz. The observations were made with the 0.76 m Jungfraujoch telescope at 3,600 m on February 1981. In this paper we present high resolution observations and mapping of the sun between 393.6 μm and 513.0 μm and observations of the moon and Jupiter at 432.6 μm. The previously observed CO J = 6 -> 5 transition by Fetterman et al. (1) has been confirmed.