|This article does not cite any references or sources. (April 2009)|
A sun outage, sun transit or sun fade 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.
In the northern hemisphere, sun outages occur before the March equinox (February, March) and after the September equinox (September and October), and in the southern hemisphere the outages occur after the March equinox and before the September equinox. 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 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.
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.
Saint Helena suffers from island-wide loss of Internet and telecommunications connections during sun outages because all telecommunications traffic to and from the island is carried on a single satellite link. Sun outage times are published in local newspapers.
As the majority of rural Alaska is served by satellite, population centers like Barrow, Alaska, Kotzebue, Alaska, and Nome, Alaska suffer from this as well. Nome is the terminus of the annual Iditarod Trail Sled Dog Race, and due to its timing, announcements of the finishers are often delayed during these sun outages.