Twice per year, every geostationary communication satellite is seen from the Earth with the Sun transiting behind it, causing the receivers whose beams are directed towards this satellite to pick up an interfering noise due to the solar microwave radiation. The assessment of this additional noise is of great importance not only in satellite broadcasting, but also in nowcasting and climate change monitoring applications, when opportunistic rainfall measurement based on satellite downlinks is employed. As matter of fact, the latter case requires accurate real-time measurement of the received signal level and prompt management of non-rain related alterations. This paper illustrates an experimental campaign, carried out during a solar transit behind a Ku-band broadcasting satellite, and provides a numerical evaluation of the Sun noise temperature.