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Around the spring and autumn (fall) equinoxes, when the day and night are about the same length, the sun crosses the equator and traces an arc that is directly behind the geo-arc of satellites. This momentarily disrupts satellite reception and causes a phenomenon known as a solar or sun outage. The exact date, time and duration of such events depends on the receive site location, the satellite in question, the earth station antenna beamwidth or focal resolution, the station keeping accuracy of the satellite and the accuracy of antenna pointing.
The sun is a powerful broadband microwave transmitter and has a noise temperature in excess of 25000K. As the sun passes directly behind the satellite, when viewed from earth, reception may be degraded or sometimes even swamped by the overwhelming noise from the sun. The observable result ranges from impulse noise (sparklies) on an FM system to total loss of signal. Digital systems appear to be a little more resilient in this respect. The outage may last several minutes either side of the peak each day during the season and will last longer the smaller the antenna. Similarly the event will occur for several days both before and after the peak day, thus outages will occur at roughly the same time each day and may repeat on a daily basis for a week or more.
Damage to equipment is possible due to the radiated heat from the sun being focussed onto the head unit but it's rare with recent designs.
A precise knowledge of when these events occur is useful. If you booked transponder time to relay, say, a news feed and it happened just to coincide with a sun outage on the downlink you might be a little upset. You could use the advance information to book a transponder at an alternative time or on an another satellite.
An accurate astronomical algorithm is used to calculate the position of the sun so solar outage events associated with a particular location and satellite combination can be predicted. Events are listed in date order and grouped into early and late seasons.
IMPORTANT: If elderly satellites have lapsed into severe inclined orbits, results may not be accurate. The module assumes reasonable station keeping accuracy. Always check the satellite's inclination before releasing any predictions
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