What is sun Outage

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 K_u-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) remain closed from 11:25 to 12:05 during 'sun outages'. 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. In September 2006, however, only the NSE intends to shut down during the sun outage; the BSE does not. The reason for which is unknown. In March 2007, the BSE & NSE had closed due to Sun outage between 11:45am to 12:30pm.

Ref: Wikipedia