A Sun outage, Sun transit, or Sun fade is an interruption in or distortion of geostationary satellite signals caused by interference (background noise) of the Sun when it falls directly behind a satellite which an Earth station is trying to receive data from or transmit data to. It usually occurs briefly to such satellites twice per year and such Earth stations install temporary or permanent guards to their receiving systems to prevent equipment damage.
Sun outages occur before the March equinox (in February and March) and after the September equinox (in September and October) for the Northern Hemisphere, and occur after the March equinox and before the September equinox for the Southern Hemisphere. At these times, the apparent path of the Sun across the sky takes it directly behind the line of sight between an Earth station and a satellite. The Sun radiates strongly across the entire spectrum, including the microwave frequencies used to communicate with satellites (C band, Ku band, and Ka band), so the Sun swamps the signal from the satellite. The effects of a Sun outage range from partial degradation (increase in the error rate) to the total destruction of the signal. The effect sweeps from north to south from approximately 20 February to 20 April, and from south to north from approximately 20 August to 20 October, affecting any specific location for less than 12 minutes a day for a few consecutive days.