With television broadcasting, the internet, communications, and navigation relying on satellites, a sudden signal interruption may seem like a technical malfunction, but sometimes it is the result of a natural astronomical phenomenon known as solar outage.
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This occurs when the sun, satellite, and terrestrial antenna are on approximately the same line of sight, so that strong solar radiation reaches the antenna in the same range in which it receives the satellite signal.
Imagine a person trying to hear a quiet speaker while behind him is a very powerful loudspeaker, the speaker being the satellite, the ear being the terrestrial antenna, and the sun being the source of noise that overwhelms the weak signal.
This is not a solar flare or solar storm, but rather the natural light and radio radiation constantly emitted by the sun. Experts confirm that solar activity can affect communications, navigation, and satellites in various ways, but the solar interference here is caused by the geometric alignment of celestial bodies and the antenna.
Why does it appear near the equinoxes?
This interference occurs regularly, especially around the spring and autumn equinoxes, when the sun crosses the celestial equator. During this period, the sun appears in front of geostationary satellites, as seen from some ground stations, and enters directly or very close to the antenna's receiving beam.
Satellites in geostationary orbit are most closely linked to this phenomenon because they orbit the Earth at an altitude of approximately 36,000 kilometers above the equator, completing a revolution every 24 hours. From Earth, they appear to be in a nearly constant position. This allows for a fixed antenna orientation, enabling the calculation of the days and times when the sun passes in front of them.
The duration of interference varies depending on the ground station's location, antenna size, and frequency used, but it usually doesn't last long. Therefore, satellite operators can predict its timing in advance and take measures to address it.
Not all moons are equally affected
The well-known impact of solar interference is concentrated on geostationary satellite services, such as television broadcasting and some telecommunications services. Low Earth orbit satellites, which typically orbit at altitudes of around 2,000 kilometers, move much faster relative to the ground station and therefore do not experience the same seasonal pattern of interference.
When the sun falls within the antenna's receiving beam, its radiation raises the noise level, and the signal-to-noise ratio decreases until the receiver can no longer clearly distinguish the signal.
In home satellite broadcasting, many services use the "Ku" band, so the viewer may notice a slight interruption in the picture or sound for a few minutes when the sun aligns with the direction of the satellite.
A phenomenon that can be predicted, not prevented.
Satellite operators cannot prevent the sun from appearing in line of sight, but they can accurately calculate the timing of interference in advance and then design communication systems with adequate margins to handle increased noise. Solutions may include using more resilient encoding and modulation techniques, or utilizing alternative paths or satellites in networks that allow for this.
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