What are they ?
In March / April and September / October day and night are about the same length. At these times of year the sun crosses the equator and it traces an arc that places it directly behind the broadcast geostationary satellites.
This can cause a strange phenomenon known as a solar (or sun) outage. This is a disruption to satellite reception for a few minutes each day for a few days. The exact date, time and duration of such events depends on the receive site location, the satellite in question, the size of the dish on your house, the station keeping accuracy of the satellite and how accurate your dish points at the satellites.
As these events can be accurately predicted for each satellite, the events are announced well in advance. In recent years, I have seen the BBC Weather service advising viewers that an outage is likely. An outage only ever last for a few minutes, since the Sun continually tracks round its orbit. After a few minutes, the Sun moves on past the satellite, and your pictures re-appear.
What causes it ?
Solar Outage results because the sun is a powerful broadband microwave source and has a noise temperature well in excess of 25,000 degrees Celcius. As the sun passes directly behind the satellite (when viewed from earth), reception of the relatively weak satellite signals is affected. The degree of interference varies from slight signal degradation to complete loss of signal as the downlink is swamped by the noise from the sun.
An outage may last several minutes each day during the interference season and will last longer the smaller the antenna involved. A 40cm dish will have a longer period of interference than a 120cm dish. This is because a small dish has a greater signal acceptance angle than a big dish.
An outage event can occur for several days both before and after the peak day. Outages will occur at roughly the same time each day and may repeat on a daily basis for a week or more.
On line resources
Georges Jullien has a web page which gives hours when the sun is behind a satellite of given longitude for a given location (latitude longitude).
The Australian Space Weather Agency has an on line predictor which is easy to use as long as you know your longitude and latitude.
And heres another one
If you run across any other good online resources I should link to, let me know.
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