A sun outage is an interruption in or distortion of geostationary satellite signals caused by interference from solar radiation. The effect is due to the sun's radiation overwhelming the satellite signal. Generally, sun outages occur in February, March, September and October, that is, around the time of the equinoxes. 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. As the sun radiates strongly at the microwave frequencies used to communicate with satellites (C-band and Ku-band) the sun swamps the signal from the satellite. The effects of a sun outage can include partial degradation, that is, an increase in the error rate, or total destruction of the signal.
Effect on Indian Stock Exchanges
In India, the BSE (Bombay Stock Exchange) and NSE (National Stock Exchange) use VSATs (Very Small Aperture Terminal) for members to connect to their trading systems. VSATs depend upon satellites for connectivity between the terminals/systems. Hence these exchanges are affected due to the sun outage. These exchanges normally remain closed from 11:45 to 12:30 during 'sun outages', but times vary depending on the scientific factors. The interference in satellite signals disturbs smooth transmission of data of online transactions, hence these share markets remain closed for the duration of sun outages. Due to these outages, the trading sessions are normally extended in the same day to compensate for the lost time. In September 2006, however, only the NSE intended to shut down during the sun outage; the BSE did not. The reason for which is unknown.