Hi. this is a small copy & paste affair. for a very good explanation, best you follow that link.
Geostationary satellites are stationed at approximately 22,300 miles (36,000 kilometers) from Earth and located directly over the equator. Given the equator is offset by 22.5 degrees, the sun aligns directly with satellites and receiving earth stations twice a yearonce in the spring and once in the autumn (Figure 1). This event is called a sun outage, and is also known as sun fade or sun transit.
The heat emitted by the sun is an intense source of noise radiated at all frequencies, including the frequency range communication satellites use. That noise is called thermal noise. When the sunand its thermal noisealigns perfectly with a satellite and the receive antenna on the ground (line-of-sight), the the noise floor, as seen by the receive earth station, is significant enough that it rises above the satellites carrier signal and causes a temporary loss of reception (Figure 2).
http://www.intelsat.com/tools-resources/satellite-basics/satellite-sun-interference/
